vocabulary c12l03c12. dominant & recessive allele - alternative form that a single gene may have...
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Vocabulary
Genetics
C12L03C12
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Allele - alternative form that a single gene may have for a particular trait (dominant & recessive)
Dihybrid – a genetic cross to examine the possible inheritance of two specific alleles (traits) (e.g. flower color & plant height)
Dominant - stronger of two genes expressed in the hybrid; represented by a capital letter (R). Masks recessive alleles.
Codominance – Pattern where phenotypes of both homozygous parents are produced in heterozygous offspring so that both alleles for a gene are equally expressed. (e.g. a cross between a red cow (RR) and a white cow (WW) produce red a white (RW) spotted cows)
Genetics Vocabulary
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F1 generation - the first-generation offspring in a breeding experiment. (1st filial generation, your parents)
F2 generation - the second-generation offspring in a breeding experiment. (2nd filial generation, you)
Gene - a unit of heredity; a sequence of DNA nucleotides that determines a single characteristic.
Genetics - science of heredity
Genetics Vocabulary
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Genotype – gene or allele combination for a trait. This is the letter combination for the genes. (e.g. RR, Rr, rr)
Heredity - passing of traits from parent to offspring
Heterozygous or Hybrid - gene combination of one dominant & one recessive allele (e.g. Rr)
Homozygous or true breeding (pure) -gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr)
Genetics Vocabulary
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Incomplete Dominance – Pattern where one allele is not completely dominant over the other. Generally displays a new trait. (Parents = Red Flower (RR), and White Flower (rr); Offspring are all Rr with Pink flowers)
Law of Independent Assortment - Mendelian law stating that a random distribution of alleles occurs during the formation of gametes.
Law of Segregation - Mendelian law stating that two alleles for each trait separate during meiosis
Monohybrid – a genetic cross involving a single trait e.g. flower color
Genetics Vocabulary
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Parental P1 Generation - the parental generation in a breeding experiment.(your grandparents)
Pedigree – Graphic representation of genetic inheritance used by geneticists to map genetic traits.
Phenotype – Physical expression of the gene. The observable characteristic that is expressed as a result of genotype (e.g. red, white)
Polygenic Traits – traits controlled by two or more genes; genes may be on the same or different chromosomes
Genetics Vocabulary
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Punnett Square - a diagram used to analyze the possible gene combinations of the offspring between two individuals. ( genotypes and phenotypes)
Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r). Is not seen if a dominant allele is present.
Sex Linked Traits – traits controlled by genes located on sex chromosomes ( X and Y chromosomes)
Trait — characteristic that is inherited; can be either dominant or recessive
Genetics Vocabulary
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Mendelian Genetics
Genetics
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Known as the “father of genetics”Austrian MonkStudied the inheritance of traits in
pea plantsDeveloped the rule of dominance
and laws of inheritanceMendel's work was not recognized
until the turn of the 20th century
Gregor Johann Mendel(1822 -1884)
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Can be grown in a small area
Produce lots of offspring very quickly
Produce pure plants when allowed to self-pollinate several generations
Can be artificially cross – pollinated
Why Peas, Pisum sativum?
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Eight Pea Plant Traits
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1. Seed shape --- Round (R) or Wrinkled (r)2. Seed Color ---- Yellow (Y) or Green (y)3. Pod Shape --- Smooth (S) or Wrinkled (s)4. Pod Color --- Green (G) or Yellow (g)5. Seed Coat Color ---Gray (G) or White (g)6. Flower position ---Axial (A) or Terminal (a)7. Plant Height --- Tall (T) or Short (t)8. Flower color --- Purple (P) or white (p)
He studied only one trait at a time to control variables, and he analyzed his data
mathematically.
Eight Pea Plant TraitsPhenotype
Genotype
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Pollen contains sperm which is produced by the stamen Ovary (found inside the flower) contains eggs
Reproduction in Flowers
stamen pistol
ovary
• Pollen carries sperm to the eggs for fertilization• Self-fertilization can occur in the same flower• Cross-fertilization can occur between flowers
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Mendel’s Experiments
Mendel cross-pollinated flowers using a paintbrush
He could snip the stamens to prevent self-pollination
He traced traits through the several generations
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Mendel’s Experiment
Mendel produced pure strains by allowing the plants to self-pollinate for several generations
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Mendel’s first experiments are called monohybrid crosses because mono
means “one” and the two parent plants differed from each other by a
single trait like height
Mendel’s Monohybrid Cross
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Used to help solve genetic problemsPunnett Squares
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Punnet SquaresWhen recording the
results of crosses, it is customary to use the same letter for different alleles of the same gene.
An uppercase letter is used for the dominant allele and a lowercase letter for the recessive allele.
The dominant allele is always written first.
Tall plantT T
T
T
Short plantt t
t
t
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Mendel cross-pollinated a tall pea plant with pollen from a short pea
plant
Generations (P1 generation; both true
breed)
T T
t
t
Shortpea plant
Tallpea plant
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All of their offspring were as tall or taller than the parent plants.
Generations (F1 generation)
T T
t
t
Tt Tt
Tt Tt
Shortpea plant
Tallpea plant
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These plants were allowed to self pollinate
Generations (F1 generation)
T t
T
t
Tallpea plant
Tallpea plant
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Three-fourths of the plants were as tall as the tall plants in the parent and first
generations and One-fourth of the offspring were as short as the short
plants in the parent generation.
Generations (F2 generation)
T t
T
t
T T T t
T t tt
Tallpea plant
Tallpea plant
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Generations Summary
P1
Short pea plant
Tall pea plant
F1
All tall pea plants
F2 3 tall: 1
short
• Parent generation (P1) produced all tall pea plants. (F1)• Short phenotype
disappeared• First generation
(F1)• A cross of two
offspring from P1• Produce F2
• Second generation (F2)• Short phenotype
reappears
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In every case, he found that one trait of a pair seemed to disappear in the F1 generation, only to reappear unchanged in one-fourth of the F2 plants.
Mendel concluded that each organism has two factors that control each of its traits.
We now know that these factors are genes and that they are located on chromosomes.
Mendel’s Conclusions
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An organism’s two alleles are located on different copies of a chromosome—one inherited from the female parent and one from the male parent.
Mendel called the observed trait dominant and the trait that disappeared recessive.
The Rule of Dominance
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Mendel’s experiments helped him formulate the 2 laws of
inheritance.
1. The law of segregationAnd
2. The law of independent assortment
Mendel’s Laws of Inheritance
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States that every individual has two alleles of each gene and when gametes are produced, each gamete receives
one of these alleles.
During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other.
Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.
Law of Segregation
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Applying the Law of Segregation
TALLSHOR
T
Tt
TtTt
TtTT
tt
T
T
t
t
Female Parent
Male Parent
Male Gametes
Female Gametes
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An Example: Your mother has the recessive gene for a
unibrow (uu), Your father has the dominant gene for two eyebrows (UU)MOM DAD
Genotype: Uu
Phenotype: two eyebrows
YOU
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States that genes (traits) for different traits—for example, seed shape and seed color—are inherited independently of each other.
This law can be illustrated using dihybrid crosses.
Law of Independent Assortment
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Monohybrid Crosses
Genetics
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Genotypes VS. Phenotypes
Genotype Possibilities: RR, Rr, rrPhenotype Possibilities: Red or White
Red (R) Dominant – White (r) Recessive
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Trait: Seed ShapeAlleles: R – Roundr – WrinkledCross: Round seeds x Wrinkled
seeds RR x rr
P1 Monohybrid Cross
R
R
rr
Rr
RrRr
Rr
Genotype: Rr
Phenotype: Round
GenotypicRatio: All alike
PhenotypicRatio: All alike
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P1 Monohybrid Cross Review
Homozygous dominant X Homozygous recessive
Offspring all Heterozygous (hybrids)
Offspring called F1 generationGenotypic & Phenotypic ratio is ALL ALIKE
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Trait: Seed ShapeAlleles: R – Roundr – WrinkledCross: Round seeds x Round seeds
Rr x Rr
F1 Monohybrid Cross
R
r
rR
RR
rrRr
Rr
Genotype: RR, Rr, rr
Phenotype: Round & wrinkled
G.Ratio: 1:2:1
P.Ratio: 3:1
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F1 Monohybrid Cross Review
Heterozygous X HeterozygousOffspring:25% Homozygous dominant RR50% Heterozygous Rr25% Homozygous Recessive rr
Offspring called F2 generationGenotypic ratio is 1:2:1Phenotypic Ratio is 3:1