Dihybrid Crosses and Other Patterns of Inheritance

Dihybrid Cross a mating of two organisms that are different in two observable traits must use a two-gene Punnett Square to solve (16 total boxes)

Dihybrid Cross Two Trait Punnett Squares

One Trait Punnett Squares and the Law of Segregation Punnett Squares show two alleles from one parent splitting up demonstrates Mendel’s Law of Segregation homologous chromosomes that carry the same genes split during Meiosis 1 allows offspring created to have one allele for each gene from each parent

Studying Heredity Holt Biology, pg. 170

Punnett Square

Two Traits and Mendel’s Laws when creating possible gametes in dihybrid cross Punnett Squares, each allele may combine with dissimilar gene alleles but not with similar gene alleles

Dihybrid Cross Two Trait Punnett Squares

Two Traits and Mendel’s Laws

Two Traits and Mendel’s Laws when creating possible gametes in dihybrid cross Punnett Squares, each allele may combine with dissimilar gene alleles but not with similar gene alleles “R” may combine with “Y” or “y” but not with “r”

Two Traits and Mendel’s Laws

Two Traits and Mendel’s Laws when creating possible gametes in dihybrid cross Punnett Squares, each allele may combine with dissimilar gene alleles but not with similar gene alleles “R” may combine with “Y” or “y” but not with “r” demonstrates Mendel’s Laws of Segregation and Independent Assortment

Dihybrid Cross Example A plant that is heterozygous for seed shape (Rr) and heterozygous for seed color (Yy) is self-pollinated. What will the genotypic and phenotypic ratios be of the offspring?

Allele Identification: Dihybrid Cross Example A plant that is heterozygous for seed shape (Rr) and heterozygous for seed color (Yy) is self-pollinated. What will the genotypic and phenotypic ratios be of the offspring? Allele Identification: Seed Shape: R = round, r = wrinkled Seed Color: Y = yellow, y = green

Parent Genotype Identification: Dihybrid Cross Example A plant that is heterozygous for seed shape (Rr) and heterozygous for seed color (Yy) is self-pollinated. What will the genotypic and phenotypic ratios be of the offspring? Parent Genotype Identification: Parent #1: RrYy Parent #2: RrYy

How many different gametes can a RrYy plant make? 4 RY Ry rY ry

What law explains why 2 Rs cannot be in the same gamete? Law of Segregation

What law explains why each “R” allele could be in a gamete with each Y allele? Law of Independent Assortment

Dihybrid Example Punnett Square

Dihybrid Example Punnett Square Parent RrYy

Dihybrid Example Punnett Square Parent RrYy RY Ry rY ry

Dihybrid Example Punnett Square Parent RrYy RY Ry rY ry RRYY RRYy RrYY RRyy Rryy rrYY rrYy rryy

Dihybrid Cross Example Phenotypic Ratio:

Begin by listing all of the possible phenotype combinations.

Dihybrid Cross Example Phenotypic Ratio: Round & Yellow: Round & Green Wrinkled & Yellow Wrinkled & Green

Then count them in the Punnett Square.

Dihybrid Example Punnett Square Parent RrYy RY Ry rY ry RRYY RRYy RrYY RRyy Rryy rrYY rrYy rryy

Dihybrid Cross Example Phenotypic Ratio: Round & Yellow: 9 Round & Green: Wrinkled & Yellow: Wrinkled & Green:

Dihybrid Cross Example Phenotypic Ratio: Round & Yellow: 9 Round & Green: 3 Wrinkled & Yellow: Wrinkled & Green:

Dihybrid Cross Example Phenotypic Ratio: Round & Yellow: 9 Round & Green: 3 Wrinkled & Yellow: 3 Wrinkled & Green:

Dihybrid Cross Example Phenotypic Ratio: Round & Yellow: 9 Round & Green: 3 Wrinkled & Yellow: 3 Wrinkled & Green: 1

Polygenic Inheritance several genes influencing one trait must use separate letters for separate genes but both genes influence the same trait Example in humans: height, weight, hair color, and skin color

We won’t use a Punnett Square with this type of inheritance.

Polygenic Inheritance in Labs two genes determine the fur coat color of a Labrador Retriever. B gene – determines skin color BB & Bb – Black skin bb – Brown skin

Polygenic Inheritance in Labs two genes determine the fur coat color of a Labrador Retriever. E gene – determines expression of pigment in fur EE & Ee – Fur color will be identical to skin pigment color (black or brown) ee – Fur color will be yellow BB & Bb – Black skin bb – Brown skin

Polygenic Inheritance in Labs

Polygenic Inheritance Twins!

Polygenic Inheritance in Horses “B” gene for hair color brown coat color (B) is dominant over tan (b) “C” gene for pigment production in hair pigment production (C) is dominant gene (C) over the absence of pigment (c) a homozygous recessive for the second gene (cc), it will have a white coat regardless of the genetically programmed coat color (B gene) because pigment is not deposited in the hair

Polygenic Inheritance in Horses

Environmental influences conditions around organisms also influence their phenotype

Environmental influences

Environmental influences

Environmental influences conditions around organisms also influence their phenotype Examples in humans: height and weight are influenced by nutrition, skin and hair color are influenced by exposure to UV radiation

Allele Identification: In rabbits, a black coat is due to a dominant gene (B), and a white coat to its recessive allele (b). Short hair length (H) is due to a dominant gene, and long hair to its recessive allele (h). In a cross between a heterozygous black, homozygous longhaired rabbit and a homozygous white, heterozygous shorthaired rabbit, what will the phenotypes be? Allele Identification: B = black fur b = white fur H = short hair h = long hair

Parent Genotype Identification: In rabbits, a black coat is due to a dominant gene (B), and a white coat to its recessive allele (b). Short hair length (H) is due to a dominant gene, and long hair to its recessive allele (h). In a cross between a heterozygous black, homozygous longhaired rabbit and a homozygous white, heterozygous shorthaired rabbit, what will the phenotypes be? Parent Genotype Identification: Black, long haired parent Bbhh White, short haired parent bbHh

Dihybrid Practice Problem #1 Parents Bbhh & bbHh Bh bh bH BbHh bbHh Bbhh bbhh

Offspring Phenotypic Ration: In rabbits, a black coat is due to a dominant gene (B), and a white coat to its recessive allele (b). Short hair length (H) is due to a dominant gene, and long hair to its recessive allele (h). In a cross between a heterozygous black, homozygous longhaired rabbit and a homozygous white, heterozygous shorthaired rabbit, what will the phenotypes be? Offspring Phenotypic Ration: Black short hair: 4 Black long hair: 4 White short hair: 4 White long hair: 4

Offspring Phenotypic Ration: In rabbits, a black coat is due to a dominant gene (B), and a white coat to its recessive allele (b). Short hair length (H) is due to a dominant gene, and long hair to its recessive allele (h). In a cross between a heterozygous black, homozygous longhaired rabbit and a homozygous white, heterozygous shorthaired rabbit, what will the phenotypes be? Offspring Phenotypic Ration: Black short hair: 1 Black long hair: 1 White short hair: 1 White long hair: 1

Allele Identification: In tomatoes, red fruit color (R) is dominant to yellow (r). Round shaped fruit (F) is dominant to pear shaped fruit (f). A gardener crosses a heterozygous red fruit, homozygous round fruit plant with a yellow fruit, heterozygous round fruit plant. Record the phenotypic ratios of the offspring. Allele Identification: R = red fruit r = yellow fruit F = round fruit f = pear shaped fruit

Parent Genotype Identification: In tomatoes, red fruit color (R) is dominant to yellow (r). Round shaped fruit (F) is dominant to pear shaped fruit (f). A gardener crosses a heterozygous red fruit, homozygous round fruit plant with a yellow fruit, heterozygous round fruit plant. Record the phenotypic ratios of the offspring. Parent Genotype Identification: Red Round Parent RrFF Yellow Round Parent rrFf

Dihybrid Practice Problem #2 Parents RrFF & rrFf RF rF RrFF rrFF rf RrFf rrFf

Offspring Phenotypic Ration: In tomatoes, red fruit color (R) is dominant to yellow (r). Round shaped fruit (F) is dominant to pear shaped fruit (f). A gardener crosses a heterozygous red fruit, homozygous round fruit plant with a yellow fruit, heterozygous round fruit plant. Record the phenotypic ratios of the offspring. Offspring Phenotypic Ration: Red round: Red pear: Yellow round: Yellow pear:

Offspring Phenotypic Ration: In tomatoes, red fruit color (R) is dominant to yellow (r). Round shaped fruit (F) is dominant to pear shaped fruit (f). A gardener crosses a heterozygous red fruit, homozygous round fruit plant with a yellow fruit, heterozygous round fruit plant. Record the phenotypic ratios of the offspring. Offspring Phenotypic Ration: Red round: 8 Red pear: Yellow round: 8 Yellow pear:

Offspring Phenotypic Ration: In tomatoes, red fruit color (R) is dominant to yellow (r). Round shaped fruit (F) is dominant to pear shaped fruit (f). A gardener crosses a heterozygous red fruit, homozygous round fruit plant with a yellow fruit, heterozygous round fruit plant. Record the phenotypic ratios of the offspring. Offspring Phenotypic Ration: Red round: 1 Yellow round: 1