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PowerPoint Lectures Campbell Biology: Concepts & Connections, Eighth Edition REECE • TAYLOR • SIMON • DICKEY • HOGAN
Chapter 9
Lecture by Edward J. Zalisko
Patterns of Inheritance
© 2015 Pearson Education, Inc.
Introduction
• The people of Tibet live and work at altitudes above 13,000 feet, where the amount of oxygen that reaches the blood is 40% less than at sea level.
• What makes the Tibetan people so able to tolerate their harsh surroundings?
• Over the last several thousand years, the Tibetan population has accumulated several dozen genetic mutations that affect their circulatory and respiratory systems.
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© 2015 Pearson Education, Inc.
Figure 9.0-1
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Figure 9.0-2 Chapter 9: Big Ideas
Mendel’s Laws Variations on Mendel’s Laws
The Chromosomal Basis of Inheritance
Sex Chromosomes and Sex-Linked Genes
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MENDEL’S LAWS
9.1 The study of genetics has ancient roots
• The Greek physician Hippocrates explained inheritance by proposing that
• particles called “pangenes” travel from each part of an organism’s body to the eggs or sperm and
• characteristics acquired during the parents’ lifetime could be transferred to the offspring.
• Hippocrates’s idea is incorrect in several respects. • The reproductive cells are not composed of
particles from somatic (body) cells. • Changes in somatic cells do not influence eggs and
sperm. © 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
Figure 9.1
9.1 The study of genetics has ancient roots
• The idea that hereditary materials mix in forming offspring, called the blending hypothesis, was
• suggested in the 19th century by scientists studying plants but
• later rejected because it did not explain how traits that disappear in one generation can reappear in later generations.
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9.2 The science of genetics began in an abbey garden
• Heredity is the transmission of traits from one generation to the next.
• Genetics is the scientific study of heredity. • Gregor Mendel
• began the field of genetics in the 1860s, • deduced the principles of genetics by breeding
garden peas, and • relied upon a background of mathematics, physics,
and chemistry.
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© 2015 Pearson Education, Inc.
Figure 9.2a
9.2 The science of genetics began in an abbey garden
• In 1866, Mendel • correctly argued that parents pass on to their
offspring discrete “heritable factors” and • stressed that the heritable factors (today called
genes) retain their individuality generation after generation.
• A heritable feature that varies among individuals, such as flower color, is called a character.
• Each variant for a character, such as purple or white flowers, is a trait.
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9.2 The science of genetics began in an abbey garden
• Perhaps the most important advantage of pea plants as an experimental model was that Mendel could strictly control matings.
• The petals of the pea flower almost completely enclose the reproductive organs: the stamens and carpel.
• Consequently, pea plants usually are able to self-fertilize in nature.
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© 2015 Pearson Education, Inc.
Figure 9.2b
Petal
Carpel (contains eggs)
Stamens (release sperm-containing pollen)
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Figure 9.2c-1
Parents (P) Carpel
Stamens
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Figure 9.2c-2 Stamen removal Pollen transfer
Carpel matures into pod
Parents (P) Carpel
Stamens
1 2
3
9.2 The science of genetics began in an abbey garden
• When Mendel wanted to cross-fertilize plants, he • prevented self-fertilization by cutting off the
immature stamens of a plant before they produced pollen and
• dusted its carpel with pollen from another plant to cross-fertilize the stamenless flower.
• After pollination, the carpel developed into a pod, containing seeds (peas) that he later planted.
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© 2015 Pearson Education, Inc.
Figure 9.2c-3 Stamen removal Pollen transfer
Carpel matures into pod
Seeds from pod planted
Offspring (F1)
Parents (P) Carpel
Stamens
1 2
3
4
9.2 The science of genetics began in an abbey garden
• True-breeding varieties result when self-fertilization produces offspring all identical to the parent.
• The offspring of two different varieties are hybrids. • The cross-fertilization is a hybridization, or genetic
cross. • True-breeding parental plants are the P generation. • Hybrid offspring are the F1 generation. • A cross of F1 plants produces an F2 generation.
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© 2015 Pearson Education, Inc.
Figure 9.2d-0
Purple White
Flower color
Character Traits Dominant Recessive
Flower position
Axial Terminal
Seed color
Yellow
Green
Seed shape Round Wrinkled
Pod shape Inflated Constricted
Pod color Green
Yellow
Stem length
Tall Dwarf
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Figure 9.2d-1
Character Traits Dominant Recessive
Purple White
Flower color
Flower position
Axial Terminal
Seed color Green Yellow
Seed shape Round Wrinkled
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Figure 9.2d-2
Character Traits Dominant Recessive
Yellow
Pod shape Inflated Constricted
Pod color Green
Stem length
Tall Dwarf
9.3 Mendel’s law of segregation describes the inheritance of a single character
• A cross between two individuals differing in a single character is a monohybrid cross.
• Mendel performed a monohybrid cross between a plant with purple flowers and a plant with white flowers.
• The F1 generation produced all plants with purple flowers.
• A cross of F1 plants with each other produced an F2 generation with ¾ purple and ¼ white flowers.
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© 2015 Pearson Education, Inc.
Figure 9.3a-1 The Experiment P generation (true-breeding parents)
Purple flowers White flowers
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Figure 9.3a-2 The Experiment P generation (true-breeding parents)
Purple flowers White flowers
F1 generation All plants have purple flowers
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of plants have white flowers
Figure 9.3a-3 The Experiment P generation (true-breeding parents)
Purple flowers White flowers
F1 generation
F2 generation
All plants have purple flowers
Fertilization among F1 plants (F1 × F1)
of plants have purple flowers
3 4
1 4
9.3 Mendel’s law of segregation describes the inheritance of a single character
• The all-purple F1 generation did not produce light purple flowers, as predicted by the blending hypothesis.
• Mendel needed to explain • why white color seemed to disappear in the F1
generation and • why white color reappeared in one-quarter of the F2
offspring.
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9.3 Mendel’s law of segregation describes the inheritance of a single character
• Mendel developed four hypotheses, described below using modern terminology.
1. Alleles are alternative versions of genes that account for variations in inherited characters.
2. For each character, an organism inherits two alleles, one from each parent. The alleles can be the same or different. • A homozygous genotype has identical alleles. • A heterozygous genotype has two different alleles.
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9.3 Mendel’s law of segregation describes the inheritance of a single character
3. If the alleles of an inherited pair differ, then one determines the organism’s appearance and is called the dominant allele. The other has no noticeable effect on the organism’s appearance and is called the recessive allele. • The phenotype is the appearance or expression of
a trait. • The genotype is the genetic makeup of a trait. • The same phenotype may be determined by more
than one genotype.
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9.3 Mendel’s law of segregation describes the inheritance of a single character
4. A sperm or egg carries only one allele for each inherited character because allele pairs separate (segregate) from each other during the production of gametes. This statement is called the law of segregation. • The fusion of gametes at fertilization creates allele
pairs once again.
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9.3 Mendel’s law of segregation describes the inheritance of a single character
• Mendel’s hypotheses also explain the 3:1 ratio in the F2 generation.
• The F1 hybrids all have a Pp genotype. • A Punnett square shows the four possible
combinations of alleles that could occur when these gametes combine.
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© 2015 Pearson Education, Inc.
Figure 9.3b-0-1 The Explanation P generation Genetic makeup (alleles)
Purple flowers White flowers PP
Gametes All
pp
P p All
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Figure 9.3b-0-2 The Explanation P generation Genetic makeup (alleles)
Purple flowers White flowers PP
Gametes All
pp
Pp
P
P
p
p
All
All F1 generation (hybrids)
Alleles segregate
Gametes 1 2
1 2
© 2015 Pearson Education, Inc.
Figure 9.3b-0-3 The Explanation P generation Genetic makeup (alleles)
Purple flowers White flowers PP
Gametes All
PP
pp
Pp
pp
Pp
Pp
P
P
P
P
p
p
p
p
All
All F1 generation (hybrids)
F2 generation
Alleles segregate
Gametes
Fertilization
Sperm from F1 plant
Phenotypic ratio 3 purple : 1 white Eggs
from F1 plant Genotypic ratio
1 PP : 2 Pp : 1 pp
1 2
1 2
Results
Results:
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Figure 9.3b-1
PP
pp
Pp
Pp
P
P
p
p F2 generation
Sperm from F1 plant
Phenotypic ratio 3 purple : 1 white Eggs
from F1 plant Genotypic ratio
1 PP : 2 Pp : 1 pp
Results
Results:
9.4 Homologous chromosomes bear the alleles for each character
• A locus (plural, loci) is the specific location of a gene along a chromosome.
• For a pair of homologous chromosomes (homologs), alleles of a gene reside at the same locus.
• Homozygous individuals have the same allele on both homologs.
• Heterozygous individuals have a different allele on each homolog.
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© 2015 Pearson Education, Inc.
Figure 9.4
Gene loci Dominant allele
Recessive allele
Homologous chromosomes
Genotype: Homozygous for the dominant allele
Homozygous for the recessive allele
Heterozygous, with one dominant and one recessive allele
PP
P
P a
a
aa
B
b
Bb
9.5 The law of independent assortment is revealed by tracking two characters at once
• A dihybrid cross is a mating of parental varieties that differ in two characters.
• Mendel performed the following dihybrid cross with the following results:
• P generation: round yellow seeds × wrinkled green seeds
• F1 generation: all plants with round yellow seeds • F2 generation:
• 9/16 had round yellow seeds • 3/16 had wrinkled yellow seeds • 3/16 had round green seeds • 1/16 had wrinkled green seeds
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© 2015 Pearson Education, Inc.
Figure 9.5a-0
P generation
Gametes
F1 generation Sperm
F2 generation
Sperm
Eggs Eggs
Results:
Yellow round Green round Yellow wrinkled Green wrinkled
The hypothesis of dependent assortment Not actually seen; hypothesis refuted
The hypothesis of independent assortment Actual results; hypothesis supported
RRYY
RRYY RrYY RRYy RrYy
RrYY rrYY RrYy rrYy
RRYy RrYy
RrYy
RrYy
RRyy Rryy
Rryy rryy rrYy
rryy
RY
Ry
RY
RY
RY Ry
RY rY
rY ry
ry
ry
ry
ry
1 2
1 2
1 2
1 4
1 4
1 4
1 4
1 4
1 4
1 4
1 4
9 16
1 16
3 16
3 16
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Figure 9.5a-1
P generation
Gametes
RRYY rryy
RY ry
F1 generation RrYy
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1 2
1 2
1 2
Figure 9.5a-2
F2 generation
Sperm
Eggs
The hypothesis of dependent assortment Not actually seen; hypothesis refuted
RY
RY
ry
ry
F1 generation RrYy
1 2
© 2015 Pearson Education, Inc.
1 4
1 4
1 4
1 4
1 4
1 4
1 4
1 4
Figure 9.5a-3
F1 generation
Sperm
Eggs
Results:
Yellow round Green round Yellow wrinkled Green wrinkled
The hypothesis of independent assortment Actual results; hypothesis supported
RRYY RrYY RRYy RrYy
RrYY rrYY RrYy rrYy
RRYy RrYy
RrYy
RrYy
RRyy Rryy
Rryy rryy rrYy
Ry
RY
RY Ry
rY
rY ry
ry
9 16
3 16
3 16
1 16
9.5 The law of independent assortment is revealed by tracking two characters at once
• Mendel needed to explain why the F2 offspring • had new nonparental combinations of traits and • had a 9:3:3:1 phenotypic ratio.
• Mendel • suggested that the inheritance of one character has
no effect on the inheritance of another, • suggested that the dihybrid cross is the equivalent
to two monohybrid crosses, and • called this the law of independent assortment.
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9.5 The law of independent assortment is revealed by tracking two characters at once
• The following figure demonstrates the law of independent assortment as it applies to two characters in Labrador retrievers:
• black versus chocolate color and • normal vision versus progressive retinal atrophy.
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© 2015 Pearson Education, Inc.
Figure 9.5b-0
Phenotypes
Genotypes
Phenotypic ratio of the offspring
Black coat, normal vision
9 Black coat,
normal vision
Black coat, blind (PRA)
3 Black coat, blind (PRA)
Chocolate coat, blind (PRA)
Chocolate coat, normal vision
3 Chocolate coat, normal vision
1 Chocolate coat,
blind (PRA)
Mating of double heterozygotes (black coat, normal vision) B_N_ B_nn bbN_ bbnn
Blind
Blind
Blind
Blind
BbNn × BbNn
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Figure 9.5b-1
Phenotypes
Genotypes
Black coat, normal vision
Black coat, blind (PRA)
Chocolate coat, blind (PRA)
Chocolate coat, normal vision
B_N_ B_nn
bbN_ bbnn
Blind
Blind
Phenotypes
Genotypes
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Figure 9.5b-2
Blind
Blind
Phenotypic ratio of the offspring
9 Black coat,
normal vision
3 Black coat, blind (PRA)
3 Chocolate coat, normal vision
1 Chocolate coat,
blind (PRA)
Mating of double heterozygotes (black coat, normal vision) BbNn × BbNn
Phenotypic ratio of the offspring
9.6 Geneticists can use the testcross to determine unknown genotypes
• A testcross is the mating between an individual of unknown genotype and a homozygous recessive individual.
• A testcross can show whether the unknown genotype includes a recessive allele.
• Mendel used testcrosses to verify that he had true-breeding varieties of plants.
• The following figure demonstrates how a testcross can be performed to determine the genotype of a Lab with normal eyes.
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© 2015 Pearson Education, Inc.
Figure 9.6
Testcross
Genotypes
Gametes
Offspring
What is the genotype of the black dog?
Two possibilities for the black dog: or
All black 1 black : 1 chocolate
B_? bb
bb Bb Bb
Bb BB
b B
b
B
b
9.7 Mendel’s laws reflect the rules of probability
• Using his strong background in mathematics, Mendel knew that the rules of mathematical probability affected
• the segregation of allele pairs during gamete formation and
• the re-forming of pairs at fertilization. • The probability scale ranges from 0 to 1. An event
that is • certain to occur has a probability of 1 and • certain not to occur has a probability of 0.
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9.7 Mendel’s laws reflect the rules of probability
• The probability of a specific event is the number of ways that event can occur out of the total possible outcomes.
• Determining the probability of two independent events uses the rule of multiplication, in which the probability is the product of the probabilities for each event.
• The probability that an event can occur in two or more alternative ways is the sum of the separate probabilities, called the rule of addition.
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© 2015 Pearson Education, Inc.
1 2
1 2
1 2
1 2
1 2
1 2
1 4
1 4
1 4
1 4
( × )
Figure 9.7
Formation of eggs
F2 genotypes
F1 genotypes
Formation of sperm
Sperm
Eggs
Bb female Bb male
B b
B B B B
B
b
b b b b
9.8 VISUALIZING THE CONCEPT: Genetic traits in humans can be tracked through family pedigrees • The inheritance of human traits follows Mendel’s
laws. • A pedigree
• shows the inheritance of a trait in a family through multiple generations,
• demonstrates dominant or recessive inheritance, and
• can also be used to deduce genotypes of family members.
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© 2015 Pearson Education, Inc.
Figure 9.8-1
Straight hairline Widow’s peak
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Figure 9.8-2
Mating
Al Beth
Children
Evelyn Frank Gary Henry
Female Male Widow’s peak hairline trait Straight hairline trait
H: widow’s peak allele h: straight allele
KEY
Charles Debbie
Isabel Juliana
Widow’s peak Straight hairline
Kristin Lori
1ST GENERATION
2ND GENERATION
3RD GENERATION
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Figure 9.8-3
A parent with a widow’s peak who has a child with a straight hairline must be Hh.
Al Beth
Kristin has a straight hairline but her parents do not, so straight hairline must be homozygous recessive (hh).
Evelyn Frank Gary Henry
Female Male Widow’s peak hairline trait Straight hairline trait
H: widow’s peak allele h: straight allele
KEY
Charles Debbie
Isabel Juliana
Widow’s peak Straight hairline
Kristin Lori
1ST GENERATION
2ND GENERATION
3RD GENERATION
Hh Hh Hh
Hh Hh hh hh
hh
hh
hh
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Figure 9.8-4
Al Beth
Not all genotypes can be determined. Lori could be HH or Hh and there is no way to know (unless she has some children and the pedigree is extended).
Evelyn Frank Gary Henry
Female Male Widow’s peak hairline trait Straight hairline trait
H: widow’s peak allele h: straight allele
KEY
Charles Debbie
Isabel Juliana
Widow’s peak Straight hairline
Kristin Lori
1ST GENERATION
2ND GENERATION
3RD GENERATION
Hh Hh Hh
Hh Hh hh hh
hh
hh
hh
HH or
Hh
HH or
Hh
9.9 CONNECTION: Many inherited traits in humans are controlled by a single gene
• Because a trait is dominant does not mean that it is • “normal” or • more common than a recessive trait.
• Wild-type traits are • those most often seen in nature and • not necessarily specified by dominant alleles.
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Figure 9.9a-0
Dominant Traits Recessive Traits
Freckles No freckles
Normal pigmentation Albinism
Key Wild-type (more common) trait Mutant (less common) trait
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Figure 9.9a-1
Freckles
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Figure 9.9a-2
No freckles
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Figure 9.9a-3
Normal pigmentation
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Figure 9.9a-4
Albinism
9.9 CONNECTION: Many inherited traits in humans are controlled by a single gene
• The genetic disorders listed in Table 9.9 are known to be inherited as dominant or recessive traits controlled by a single gene.
• These human disorders therefore show simple inheritance patterns like the traits Mendel studied in pea plants.
• The genes discussed in this module are all located on autosomes.
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© 2015 Pearson Education, Inc.
Table 9.9
9.9 CONNECTION: Many inherited traits in humans are controlled by a single gene
• Thousands of human genetic disorders—ranging in severity from relatively mild, such as albinism, to invariably fatal, such as cystic fibrosis—are inherited as recessive traits.
• Most people who have recessive disorders are born to normal parents who
• are both heterozygotes, carriers of the recessive allele for the disorder, but
• are phenotypically normal.
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© 2015 Pearson Education, Inc.
Figure 9.9b
Parents
Offspring
Normal Aa
Sperm
Eggs
AA Normal
Normal Aa
Aa Normal (carrier)
Aa Normal (carrier)
aa Albinism
A
A
a
a
9.9 CONNECTION: Many inherited traits in humans are controlled by a single gene
• The most common lethal genetic disease in the United States is cystic fibrosis (CF). The CF allele is
• recessive and • carried by about 1 in 31 Americans.
• Cystic fibrosis is • characterized by an excessive secretion of very
thick mucus from the lungs and other organs and • most common in Caucasians.
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9.9 CONNECTION: Many inherited traits in humans are controlled by a single gene
• Dominant human disorders include • Huntington’s disease, a degenerative disorder of
the nervous system and • achondroplasia, a form of dwarfism in which
• the head and torso of the body develop normally but • the arms and legs are short.
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Figure 9.9c
9.9 CONNECTION: Many inherited traits in humans are controlled by a single gene
• Until relatively recently, the onset of symptoms was the only way to know if a person had inherited the Huntington’s allele.
• A genetic test is now available that can detect the presence of the Huntington’s allele in an individual’s genome.
• This is one of several genetic tests currently available.
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9.10 CONNECTION: New technologies can provide insight into one’s genetic legacy
• Modern technologies offer ways to obtain genetic information
• before conception, • during pregnancy, and • after birth.
• Genetic testing can identify prospective parents who are heterozygous carriers for certain diseases.
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9.10 CONNECTION: New technologies can provide insight into one’s genetic legacy
• Several technologies can be used for detecting genetic conditions in a fetus.
• Amniocentesis extracts samples of amniotic fluid containing fetal cells and permits
• karyotyping to detect chromosomal abnormalities such as Down syndrome and
• biochemical tests on cultured fetal cells to detect other conditions, such as Tay-Sachs disease.
• Chorionic villus sampling removes a sample of chorionic villus tissue from the placenta and permits similar karyotyping and biochemical tests.
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Video: Ultrasound of Human Fetus
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© 2015 Pearson Education, Inc.
Figure 9.10a-0 Amniocentesis
Ultrasound transducer
Fetus Placenta Uterus
Cervix
Needle extracts amniotic fluid.
Amniotic fluid Fetal cells
Cultured cells
Centrifugation
Several hours
Several weeks
Karyotyping
Biochemical and genetic tests
Several hours
Several hours
Several weeks
Ultrasound transducer
Fetus Placenta
Uterus Cervix
Chorionic villi
Suction tube extracts tissue from chorionic villi.
Chorionic Villus Sampling (CVS)
Fetal cells
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Figure 9.10a-1
Karyotyping
9.10 CONNECTION: New technologies can provide insight into one’s genetic legacy
• Blood tests on the mother at 15–20 weeks of pregnancy can help identify fetuses at risk for certain birth defects.
• Fetal imaging enables a physician to examine a fetus directly for anatomical deformities. The most common procedure is ultrasound imaging, using sound waves to produce a picture of the fetus.
• Newborn screening can detect diseases that can be prevented by special care and precautions.
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© 2015 Pearson Education, Inc.
Figure 9.10b-0
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Figure 9.10b-1
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Figure 9.10b-2
9.10 CONNECTION: New technologies can provide insight into one’s genetic legacy
• New technologies raise ethical considerations that include
• the confidentiality and potential use of results of genetic testing,
• time and financial costs, and • the determination of what, if anything, should be
done as a result of the testing.
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© 2015 Pearson Education, Inc.
VARIATIONS ON MENDEL’S LAWS
9.11 Incomplete dominance results in intermediate phenotypes
• Mendel’s pea crosses always looked like one of the two parental varieties, a situation called complete dominance.
• For some characters, the appearance of F1 hybrids falls between the phenotypes of the two parental varieties. This is called incomplete dominance.
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© 2015 Pearson Education, Inc.
Figure 9.11a-0 P generation
1 2
1 2
1 2
1 2
1 2
1 2
F1 generation
F2 generation
Gametes
Gametes
Eggs
Red RR
White rr
Pink hybrid Rr
Sperm
R
R
R
R
r
r
r
r
RR rR
rr Rr
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Figure 9.11a-1
P generation
Gametes
Red RR
White rr
R r
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Figure 9.11a-2
1 2
F1 generation
Gametes
Pink hybrid Rr
R r 1 2
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Figure 9.11a-3
1 2
1 2
1 2
1 2
F2 generation
Eggs
Sperm
R
R
r
r
RR rR
rr Rr
9.11 Incomplete dominance results in intermediate phenotypes
• One example of incomplete dominance in humans is hypercholesterolemia, in which
• dangerously high levels of cholesterol occur in the blood and
• heterozygotes have intermediately high cholesterol levels.
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© 2015 Pearson Education, Inc.
Figure 9.11b
Phenotypes
Mild disease Severe disease Normal Cell
LDL
LDL receptor
Genotypes HH
Homozygous for ability to make
LDL receptors
Hh Heterozygous
hh Homozygous
for inability to make LDL receptors
9.12 Many genes have more than two alleles in the population
• Although each individual carries, at most, two different alleles for a particular gene, in cases of multiple alleles, more than two possible alleles exist in a population.
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9.12 Many genes have more than two alleles in the population
• Human ABO blood group phenotypes involve three alleles for a single gene.
• The four human blood groups, A, B, AB, and O, result from combinations of these three alleles.
• The A and B alleles are both expressed in heterozygous individuals, making both alleles codominant.
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© 2015 Pearson Education, Inc.
Figure 9.12-0
Carbohydrate A
Carbohydrate B
Carbohydrate A and Carbohydrate B
Neither
Blood Group (Phenotype) Genotypes
Carbohydrates Present on Red Blood Cells
Antibodies Present in Blood
Reaction When Blood from Groups Below Is Mixed with Antibodies from Groups at Left
A O B AB
Anti-B
Anti-A
None
Anti-A
No reaction Clumping reaction
Anti-B
A
O
B
AB
IAIA or IAi
IBIB or IBi
IAIB
ii
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Figure 9.12-1
Carbohydrate A
Carbohydrate B
Carbohydrate A and Carbohydrate B
Neither
Blood Group (Phenotype) Genotypes
Carbohydrates Present on Red Blood Cells
A
O
B
AB
IAIA or IAi
IBIB or IBi
IAIB
ii
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Figure 9.12-2
Blood Group (Phenotype)
A
O
B
AB
Antibodies Present in Blood
Reaction When Blood from Groups Below Is Mixed with Antibodies from Groups at Left
A O B AB
Anti-B
Anti-A
None
Anti-A
Anti-B
9.13 A single gene may affect many phenotypic characters
• Pleiotropy occurs when one gene influences multiple characters.
• Sickle-cell disease is a human example of pleiotropy.
• This disease affects the type of hemoglobin produced and the shape of red blood cells and causes anemia and organ damage.
• Sickle-cell and nonsickle alleles are codominant. • Carriers of sickle-cell disease have increased
resistance to malaria.
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© 2015 Pearson Education, Inc.
Figure 9.13a
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Figure 9.13b An individual homozygous for the sickle-cell allele
Produces sickle-cell (abnormal) hemoglobin
The abnormal hemoglobin crystallizes, causing red blood cells to become sickle-shaped
Damage to organs Other effects Kidney failure Heart failure Spleen damage Brain damage (impaired
mental function, paralysis)
Pain and fever Joint problems Physical weakness Anemia Pneumonia and other
infections
9.14 A single character may be influenced by many genes
• Many characters result from polygenic inheritance, in which a single phenotypic character results from the additive effects of two or more genes on a single phenotypic character.
• Human skin color is an example of polygenic inheritance.
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© 2015 Pearson Education, Inc.
Figure 9.14-0 P generation
F1 generation
F2 generation
Frac
tion
of p
opul
atio
n
Skin color
Sperm
Eggs
aabbcc (very light)
AABBCC (very dark)
AaBbCc (medium shade)
AaBbCc (medium shade)
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8 1 8 1 8 1 8 1 8 1 8 1 8 1 8
1 64
1 64 1
64 6 64
6 64
6 64
15 64
15 64
15 64
20 64
20 64
© 2015 Pearson Education, Inc.
Figure 9.14-1
P generation
F1 generation
aabbcc (very light)
AABBCC (very dark)
AaBbCc (medium shade)
AaBbCc (medium shade)
© 2015 Pearson Education, Inc.
Figure 9.14-2
F2 generation
Sperm
Eggs
15 64
1 64
15 64
1 64
6 64
6 64
20 64
1 8
1 8 1 8 1 8 1 8 1 8 1 8 1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8
1 8
© 2015 Pearson Education, Inc.
Figure 9.14-3
15 64
1 64
6 64
20 64
Frac
tion
of p
opul
atio
n
Skin color
9.15 The environment affects many characters
• Many characters result from a combination of heredity and the environment. For example,
• skin color is affected by exposure to sunlight and • heart disease and cancer are influenced by genes
and the environment. • Identical twins show that a person’s traits are the
results of • genetics and • the environment.
© 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
Figure 9.15a
© 2015 Pearson Education, Inc.
Figure 9.15b
© 2015 Pearson Education, Inc.
THE CHROMOSOMAL BASIS OF INHERITANCE
9.16 Chromosome behavior accounts for Mendel’s laws
• The chromosome theory of inheritance states that • genes occupy specific loci (positions) on
chromosomes and • chromosomes undergo segregation and
independent assortment during meiosis.
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9.16 Chromosome behavior accounts for Mendel’s laws
• Mendel’s laws correlate with chromosome separation in meiosis.
• The law of segregation • states that pairs of alleles separate from each other
during gamete formation via meiosis and • depends on separation of homologous
chromosomes in anaphase I. • The law of independent assortment
• states that each pair of alleles sorts independently of other pairs of alleles during gamete formation and
• depends on alternative orientations of chromosomes in metaphase I.
© 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
Figure 9.16-1-1 F1 generation
All yellow round seeds (RrYy)
Two equally
probable arrangements
of chromosomes at metaphase I
R R
R
Y
Y Y
r r
r y
y y
© 2015 Pearson Education, Inc.
Figure 9.16-1-2 F1 generation
All yellow round seeds (RrYy)
Two equally
probable arrangements
of chromosomes at metaphase I
Anaphase I
Metaphase II R R
R R
R R
R
Y
Y Y
Y Y
Y Y
r r
r r
r r
r y
y y
y y
y y
© 2015 Pearson Education, Inc.
Figure 9.16-1-3 F1 generation
1 4
F2 generation
All yellow round seeds (RrYy)
Fertilization among the F1 plants
Gametes
9 : 3 : 3 : 1
Two equally
probable arrangements
of chromosomes at metaphase I
Anaphase I
Metaphase II
Meiosis I
Meiosis II
1 4
1 4
1 4 RY ry rY Ry
R
R R R R
R
R R
R R
R
Y
Y Y
Y Y
Y Y
Y Y Y y y y y Y
r r r r
r r
r r
r r
r y
y y
y y
y y
© 2015 Pearson Education, Inc.
Figure 9.16-2
1 4
RY
RY
rY
rY
Ry
Ry ry
ry
RRYY RrYY RRYy RrYy
RrYY rrYY RrYy rrYy
RRYy RrYy RRyy Rryy
RrYy rrYy Rryy rryy
Sperm
Eggs
Yellow round
Yellow wrinkled
Green wrinkled
Green round
9 16
1 4
1 4
1 4
1 4
1 4
1 4
1 4
3 16
3 16
1 16
9.17 SCIENTIFIC THINKING: Genes on the same chromosome tend to be inherited together • Bateson and Punnett studied plants that did not
show a 9:3:3:1 ratio in the F2 generation. What they found was an example of linked genes, which
• are located close together on the same chromosome and
• tend to be inherited together.
© 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
Figure 9.17-0 The Experiment
Purple flower
Long pollen
PpLl PpLl
Prediction (9:3:3:1)
Observed offspring
Phenotypes
Purple long Purple round Red long Red round
284 21 21 55
215 71 71 24
The Explanation: Linked Genes Parental diploid cell PpLl
Most gametes
Most offspring
Meiosis
Fertilization
Sperm
3 purple long : 1 red round Not accounted for: purple round and red long
PL
PL
pl
pl
pl
pl pl
pl
pl pl
PL
PL PL
PL
PL
PL
Eggs
© 2015 Pearson Education, Inc.
Figure 9.17-1
The Experiment
Purple flower
Long pollen
PpLl PpLl
Prediction (9:3:3:1)
Observed offspring
Phenotypes
Purple long Purple round Red long Red round
284 21 21 55
215 71 71 24
© 2015 Pearson Education, Inc.
Figure 9.17-2 The Explanation: Linked Genes
Parental diploid cell PpLl
Most gametes
Most offspring
Meiosis
Fertilization
Sperm
3 purple long : 1 red round Not accounted for: purple round and red long
PL
PL
pl
pl
pl
pl pl
pl
pl pl
PL
PL PL
PL
PL
PL
Eggs
9.18 Crossing over produces new combinations of alleles
• Crossing over between homologous chromosomes produces new combinations of alleles in gametes.
• Linked genes can be separated by crossing over, forming recombinant gametes.
• The percentage of recombinant offspring is the recombination frequency.
© 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
Figure 9.18a
Crossing over
Parental gametes
Recombinant gametes
Tetrad (pair of
homologous chromosomes)
P L
P L
P l p l
p l
p L
© 2015 Pearson Education, Inc.
Figure 9.18b
© 2015 Pearson Education, Inc.
Figure 9.18c-0
The Experiment The Explanation
Crossing over
Eggs Sperm
Female Male
Offspring
Parental Recombinant
Offspring
Gray body, long wings (wild type)
Black body, vestigial wings
GgLl Female
Gray long Black
vestigial Gray
vestigial Black long
965 944 206 185
Parental phenotypes
Recombinant phenotypes
Recombination frequency
= 391 recombinants 2,300 total offspring
= 0.17 or 17%
ggll Male
ggll GgLl
G L
G L
G L L
L
G
G
g l
g l
g l
g l g l
g l g l g l g l g l
g l
l g
© 2015 Pearson Education, Inc.
Figure 9.18c-1 The Experiment
Female Male
Offspring
Gray body, long wings (wild type)
Black body, vestigial wings
Gray long Black
vestigial Gray
vestigial Black long
965 944 206 185
Parental phenotypes
Recombinant phenotypes
Recombination frequency
= 391 recombinants 2,300 total offspring
= 0.17 or 17%
ggll GgLl
© 2015 Pearson Education, Inc.
Figure 9.18c-2
The Explanation
GgLl Female
ggll Male
Crossing over
GL
g l g l
g l
g l
g L G l GL g l
Eggs Sperm
Parental Parental Recombinant
g L G l GL g l
g l g l g l g l
9.19 Geneticists use crossover data to map genes
• When examining recombinant frequency, Alfred H. Sturtevant, one of Morgan’s students, found that the greater the distance between two genes on a chromosome, the more points there are between them where crossing over can occur.
• Recombination frequencies can thus be used to map the relative position of genes on chromosomes.
• Such a diagram of relative gene locations is called a linkage map.
© 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
Figure 9.19a
Section of chromosome carrying linked genes
9% 9.5%
17%
Recombination frequencies
© 2015 Pearson Education, Inc.
Figure 9.19b
Mutant (less common) phenotypes Short aristae
Black body (g)
Cinnabar eyes (c)
Vestigial wings (l)
Brown eyes
Long aristae (appendages on head)
Gray body (G)
Red eyes (C)
Normal wings (L)
Red eyes
Wild-type (more common) phenotypes
© 2015 Pearson Education, Inc.
SEX CHROMOSOMES AND SEX-LINKED GENES
9.20 Chromosomes determine sex in many species
• Many animals have a pair of sex chromosomes, designated X and Y, that determine an individual’s sex.
• Among humans and other mammals, • individuals with one X chromosome and one Y
chromosome are males, and • XX individuals are females.
• In addition, human males and females both have 44 autosomes (nonsex chromosomes).
© 2015 Pearson Education, Inc.
9.20 Chromosomes determine sex in many species
• In mammals (including humans), • the Y chromosome has a crucial gene, SRY, for the
development of testes, and • an absence of the SRY gene directs ovaries to
develop.
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© 2015 Pearson Education, Inc.
Figure 9.20a
X
Y
© 2015 Pearson Education, Inc.
Figure 9.20b-0
Parents (diploid)
Gametes (haploid)
Offspring (diploid)
Male Female
Sperm Egg
Male Female
44 +
XY 44 +
XX
44 +
XY 44 +
XX
22 + X
22 + Y
22 + X
© 2015 Pearson Education, Inc.
Figure 9.20b-1
© 2015 Pearson Education, Inc.
Figure 9.20b-2
© 2015 Pearson Education, Inc.
Figure 9.20b-3
© 2015 Pearson Education, Inc.
Figure 9.20b-4
9.20 Chromosomes determine sex in many species
• Grasshoppers, roaches, and some other insects have an X-O system, in which
• O stands for the absence of a sex chromosome, • females are XX, and • males are XO.
• In certain fishes, butterflies, and birds, • the sex chromosomes are Z and W, • males are ZZ, and • females are ZW.
© 2015 Pearson Education, Inc.
9.20 Chromosomes determine sex in many species
• Some organisms lack sex chromosomes altogether.
• In most ants and bees, sex is determined by chromosome number.
• Females develop from fertilized eggs and thus are diploid.
• Males develop from unfertilized eggs. Males are thus
• fatherless and • haploid.
© 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
Table 9.20-0
© 2015 Pearson Education, Inc.
Table 9.20-1
X-O system
© 2015 Pearson Education, Inc.
Table 9.20-2
Z-W system
© 2015 Pearson Education, Inc.
Table 9.20-3
Chromosome number determines sex
9.20 Chromosomes determine sex in many species
• In some animals, environmental temperature determines the sex.
• For some species of reptiles, the temperature at which the eggs are incubated during a specific period of embryonic development determines whether the embryo will develop into a male or female.
• Global climate change may therefore impact the sex ratio of such species.
© 2015 Pearson Education, Inc.
9.21 Sex-linked genes exhibit a unique pattern of inheritance
• Sex-linked genes are located on either of the sex chromosomes.
• The X chromosome carries many genes unrelated to sex.
• The inheritance of white eye color in the fruit fly illustrates an X-linked recessive trait.
© 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
Figure 9.21a-0
© 2015 Pearson Education, Inc.
Figure 9.21a-1
© 2015 Pearson Education, Inc.
Figure 9.21a-2
© 2015 Pearson Education, Inc.
Figure 9.21b Female Male
Sperm
Eggs
R = red-eye allele r = white-eye allele
X R X R X r Y
X R X r X R Y X R
Y X r
© 2015 Pearson Education, Inc.
Figure 9.21c Female Male
Sperm
Eggs
R = red-eye allele r = white-eye allele
X R X r X R Y
X R X R X R Y
X r X R X r Y
X R
X r
Y X R
© 2015 Pearson Education, Inc.
Figure 9.21d Female Male
Sperm
Eggs
R = red-eye allele r = white-eye allele
X R X r X r Y
X R X r X R Y
X r X r X r Y
X R
X r
Y X r
9.22 CONNECTION: Human sex-linked disorders affect mostly males
• Most sex-linked human disorders are • due to recessive alleles and • seen mostly in males.
• A male receiving a single X-linked recessive allele from his mother will have the disorder.
• A female must receive the allele from both parents to be affected.
© 2015 Pearson Education, Inc.
9.22 CONNECTION: Human sex-linked disorders affect mostly males
• Recessive and sex-linked human disorders include • hemophilia, characterized by excessive bleeding
because hemophiliacs lack one or more of the proteins required for blood clotting,
• red-green colorblindness, a malfunction of light-sensitive cells in the eyes, and
• Duchenne muscular dystrophy, a condition characterized by a progressive weakening of the muscles and loss of coordination.
© 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
Figure 9.22-0
Albert Queen Victoria
Alice Louis
Alexandra Czar Nicholas II of Russia
Alexis
Female Male Hemophilia
Carrier
Normal
© 2015 Pearson Education, Inc.
Figure 9.22-1
9.23 EVOLUTION CONNECTION: The Y chromosome provides clues about human male evolution • The Y chromosome provides clues about human
male evolution because • Y chromosomes are passed intact from father to
son and • mutations in Y chromosomes can reveal data about
recent shared ancestry.
© 2015 Pearson Education, Inc.
9.23 EVOLUTION CONNECTION: The Y chromosome provides clues about human male evolution • In 2003, geneticists discovered that about 8% of
males currently living in central Asia have Y chromosomes of striking genetic similarity.
• Further analysis traced their common genetic heritage to a single man living about 1,000 years ago.
• In combination with historical records, the data led to the speculation that the Mongolian ruler Genghis Kahn may be responsible for the spread of the telltale chromosome to nearly 16 million men living today
© 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
Figure 9.23
You should now be able to
1. Describe the theory of pangenes and the blending hypothesis. Explain why both ideas are now rejected.
2. Define and distinguish between true-breeding organisms, hybrids, the P generation, the F1 generation, and the F2 generation.
© 2015 Pearson Education, Inc.
You should now be able to
3. Define and distinguish between the following pairs of terms: • homozygous and heterozygous; • dominant allele and recessive allele; • genotype and phenotype. Also, define a monohybrid cross and a Punnett square.
© 2015 Pearson Education, Inc.
You should now be able to
4. Explain how Mendel’s law of segregation describes the inheritance of a single character.
5. Describe the genetic relationships between homologous chromosomes.
6. Explain how Mendel’s law of independent assortment applies to a dihybrid cross.
7. Explain how and when the rule of multiplication and the rule of addition can be used to determine the probability of an event.
© 2015 Pearson Education, Inc.
You should now be able to
8. Explain how family pedigrees can help determine the inheritance of many human traits.
9. Explain how recessive and dominant disorders are inherited. Provide examples of each.
10. Compare the health risks, advantages, and disadvantages of the following forms of fetal testing: • amniocentesis, • chorionic villus sampling, and • ultrasound imaging.
© 2015 Pearson Education, Inc.
You should now be able to
11. Describe the inheritance patterns of incomplete dominance, multiple alleles, codominance, pleiotropy, and polygenic inheritance.
12. Explain how the sickle-cell allele can be adaptive.
13. Explain why human skin coloration is not sufficiently explained by polygenic inheritance.
14. Define the chromosome theory of inheritance. Explain the chromosomal basis of the laws of segregation and independent assortment.
© 2015 Pearson Education, Inc.
You should now be able to
15. Explain how linked genes are inherited differently from nonlinked genes.
16. Describe T. H. Morgan’s studies of crossing over in fruit flies. Explain how Sturtevant created linkage maps.
17. Explain how sex is genetically determined in humans and the significance of the SRY gene.
18. Describe patterns of sex-linked inheritance and examples of sex-linked disorders.
19. Explain how the Y chromosome can be used to trace human ancestry.
© 2015 Pearson Education, Inc.
© 2015 Pearson Education, Inc.
Figure 9.UN01
Fertilization Homologous chromosomes
Alleles, residing at the same locus
Meiosis
Paired alleles, different forms of a gene Haploid gametes
(allele pairs separated)
Gamete from the other parent
Diploid zygote (containing paired alleles)
© 2015 Pearson Education, Inc.
Figure 9.UN02
Incomplete dominance
Red RR
White rr
Pink Rr
© 2015 Pearson Education, Inc.
Figure 9.UN03
Pleiotropy Single gene
Multiple characters
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Figure 9.UN04
Multiple genes
Polygenic inheritance
Single characters (such as skin color)
© 2015 Pearson Education, Inc.
Figure 9.UN05
Genes
chromosomes
heterozygous
(a)
(b) (c)
(d) (e)
(f)
located on
alternative versions called
at specific locations called
if both are the same, the genotype is called
if different, the genotype is called
the expressed allele is called
the unexpressed allele is called
inheritance when the phenotype is in between is called