ch. 10.1 mendel’s discoveries. gregor mendel (1866) “father of modern genetics” breed pea...
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Ch. 10.1 Mendel’s Discoveries
Gregor Mendel (1866)• “Father of
Modern Genetics”• Breed pea plant.
(Pre- Mendel: Blending of traits hypothesis)
Background VocabBackground VocabTrue-breeds: pure gene lines –
offspring match parent Self-pollination: pollen from flower
fertilizes the same plantCross-fertilization: pollen will
fertilize a different plantHybrid: Cross between organisms
with different traits (blonde hair & brown hair)
Trait: Physical characteristics
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Cross pollination Cross pollination
6Trait Studied Dominant Form
Recessive Form
F2 Dominant-to- Recessive Ratio
SEED SHAPE
SEED COLOR
POD SHAPE
POD COLOR
FLOWER COLOR
FLOWER POSITION
STEM LENGTH
2.96:1
3.01:1
2.95:1
2.82:1
3.15:1
3.14:1
2.84:1787 tall 277 dwarf
651 long stem 207 at tip
705 purple 224 white
152 yellow428 green
299 wrinkled882 inflated
6,022 yellow 2,001 green
5,474 round 1,850 wrinkled
Mendel’s Experimental designMendel’s Experimental design
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Parental generation (P) White X Purple (truebreed X truebreed)
Offspring: F1 Generation (Hybrids)100% purple
F1 Cross Purple X Purple
(hybrid X hybrid)
Offspring: F2(3:1 – Purple : White)
75% Dominant: 25% Recessive
MendelMendel’’s Conclusions:s Conclusions:Inheritance is determined by chemical
factors (genes) passed from one generation to the next (particulate hypothesis)
Genes can come in more than one form= alleleExample: (white vs purple)
Ch. 10.2 Mendel’s Genetics
More Genetics VocabMore Genetics Vocab• Homozygous: two identical
alleles (AA or aa)• Heterozygous: two different
alleles (Aa)• Phenotype: Physical appearance • Genotype: Genetic make-up
– Homozygous dominant (AA)– Homozygous recessive (aa)– Heterozygous (Aa)
MendelMendel’’s Principless Principles1. There are alternative forms of genes
(alleles)2. There are 2 alleles for each trait (BB,Bb,
bb) * we now know there can be more.3. Some alleles are dominant; some
recessive. 4. Principle of SEGREGATION: Alleles
for each trait segregate (separate) during gamete formation (Anaphase I of meiosis)
Monohybrid Crosses = Parents differ in only 1 trait
P: Purple X White
F1: all purple (100% dominant)F1 purples self- fertilize to see if white trait was lost.
F2: 75% purple; 25% white
(dominant) (recessive)
Diagram that shows all possible outcomes of a genetic cross
Standard Mendelian Cross #1:Standard Mendelian Cross #1:
If purple flower color is dominant, what phenotypes are expected if a purebred purple flowered plant is crossed with a purebred white flowered plant?
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WWWW x wwww
Phenotypic Ratio: 100% purple
Genotypic ratio: 100% Ww
Standard Mendelian Cross #2:Standard Mendelian Cross #2:
If purple flower color is dominant, what genotypes are expected if a heterozygote is crossed with another heterozygote.
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WwWw x WwWw
Phenotypic ratios:
3 purple: 1 white
Genotypic ratios:
1WW:2Ww:1ww
Testcross: Helps determine the genotype of a dominant phenotype
• Dominant phenotype could be AA or Aa
• Unknown Dominant X Recessive (aa)- Any recessive offspring, unknown= Aa- All dominant offspring, unknown= AA
Mendel’s DIHYBRID CROSSES(2 traits)
Independent Assortment: Alleles for different traits do not influence each other’s segregation during meiosis.
List the gamete combinations possible for each of the genotypes listed below:
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RrYY
rrYY
RrYy
RY, rY, RY, rY
rY, rY, rY, and rY
RY, Ry, rY, and ry
Dihybrid Cross
F2: 9:3:3:1 Ratio
Traits are inherited separately.
Black hair is dominant to white
Short hair is dominant to long
Cross a heterozygous black & short haired mouse with a white & heterozygous short haired mouse.
1. What are the genotypes of the parents?
2. What are the genotypic and phenotypic ratios of the F1 generation?
10.3 Exceptions to Mendel
Incomplete/Intermediate dominance: blending of phenotypesneither allele takes a fully dominant role
P1: Red x White flowers
F1: Pink flowers
F2: 1 red: 2 pink: 1 white
Codominance• BOTH alleles are expressed in heterozygotes.• Not incomplete dominance• EX: Roan cattle and Blood types
Multiple AllelesMore than 2 alleles for an inherited character.
Eye colorBlood type: A, B, AB, or O
Fur color
Blood Typing: Multiple Allelism
a) Human blood type is expressed by 3 alleles: IA, IB and i.
b) IA and IB are Co-dominant
c) i is recessive.
Codominance in blood groups
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Blood Type: Codominance & Multiple Alleles
Caucasians African American
Hispanic Asian
O + 37% 47% 53% 39%
O - 8% 4% 4% 1%
A + 33% 24% 29% 27%
A - 7% 2% 2% 0.5%
B + 9% 18% 9% 25%
B - 2% 1% 1% 0.4%
AB + 3% 4% 2% 7%
AB - 1% 0.3% 0.2% 0.1%
• Could a person with Type A blood receive type O blood? Could they receive Type AB?
• Could a person with AB- blood receive AB+?
• List the blood types that type B+ could receive?
Polygenic Inheritance: Multiple Genes affect a trait
Phenotypes of these traits demonstrate continuous continuous variationvariation (bell curve)
Examples: Examples: height, weight, skin color, intelligence.
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Continuous variation in skin Continuous variation in skin color color
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Environmental Influence on Genes
Temperature, pressure, pH, presence of certain chemical compounds influence how genes are expressed.
Epigenetics: study of how genes are influenced by environmental conditions.
Environmental Influence
1. Some flowers colors are influenced by the acidity of the soil (Hydrangea).
1. The color of the arctic fox is influenced by temperature.
2. Siamese cats have darker hair at areas that are cooler than body temperature (ears, nose and paws).
3. Human size is influenced by nutrition.
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10.5: Sex Linked Genes: Genes located on X or Y chromosome
Do you think the X chromosome or the Y chromosome holds more genes?
Rules
1. Recessive Sex Linked Traits:- Affect males more than females - Males only need one copy of the gene (XaY).- Females can be carries (XAXa)
2. Dominant Sex- Linked Traits: - More likely to affect females (XA XA or XA Xa)
Recessive Sex-Linked Disorders Color-blindness Hemophelia Baldness Versions of Muscular Dystrophy
12.3- Pedigrees
A Pedigree is a family tree that shows the inheritance of a genetic disorder
Carriers: do not have the disorder but can pass it on (heterozygous)
A pedigree can allow you to determine whether a trait is autosomal, or sex-linked.
1.1. AutosomalAutosomal disorders affect males and females equally.
1. If the trait is autosomal dominantautosomal dominant, every individual every individual who has the disorder will have at at least one parent least one parent who has the disorder.
2. If the trait is autosomal recessiveautosomal recessive, an individual with the trait can have one, two or neither parentone, two or neither parent exhibit the trait.
1. Sex-linked traits are carried on the X chromosome, and therefore affect one gender or the other in disproportionately high numbers.
a) Sex-linked recessive traits affect males in higher numbers.
• Since they have only one X chromosome, if males receive a single copy of this recessive allele, they will show the phenotype.
• Females must still receive two recessive versions to show the phenotype.
b) Sex-linked dominant traits affect females in higher numbers
• A female has two X chromosomes, and therefore is twice as likely to receive the trait
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Question: Question: Is this disorder autosomal or sex-linked?
Is it dominant or recessive?
Parents are unaffected
Both males and females are affected
Complete the following pedigrees. Which is for a sex-linked trait? How do you know?
Is it a dominant or recessive trait?
Royal Family Pedigree
Human genetic disorders
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10.4 Gene linkage
Genes located on the same chromosome tend to be linked
Loci: location of a gene on a chromosome
• Gene Linkage:
• Gene closer together on chromosome have a greater likelihood of traveling together during crossing over
• Greater likelihood of inheriting genes together
12.1Genome: the complete set of genetic material
12. 4- Genes and Cancer
• Regulation of Cell Cycle– Growth factors: Initiate cell division – Tumor Suppressor Genes: Stop Cell Division
• Cancer is ALWAYS a genetic disease due to mutations in DNA
– Mutation in somatic cells= not passed on to offspring
– If mutation occurs in ovaries or testes• offspring will inherit an abnormal copy of a gene that increases
their likelihood of developing cancer
Epigenetics
NOVA Video (13min)
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