Punnett Squares

In Hershey’s kisses, red is completely dominant to silver. The dominant red allele will hide the recessive silver allele in the heterozygote. RR rr Rr

Complete Dominance Sample Genotypes: Key Characteristics: A capital letter represents the dominant allele and a lowercase letter represents the recessive allele. The heterozygous will show only the dominant phenotype Sample Genotypes Terminology Phenotype RR Homozygous Dominant Dominant Rr Heterozygous rr Homozygous Recessive Recessive

Complex Punnett Squares

In Hershey’s kisses, red and silver are co-dominant. RR WW RW

Co-Dominance Sample Genotypes: Key Characteristics: Two alleles are dominant Capital letters are used to represent both dominant versions The heterozygous will show both in the phenotype equally Sample Genotypes Terminology Phenotype BB Homozygous Dominant Dominant 1 BW Heterozygous Both (Mix of 1 and 2) WW Dominant 2

Co-Dominance Practice In cattle, red and white are co-dominant. Roan occurs when both red and white are present. Show what would happen if a roan bull was crossed with a white cow. genotypes parents R W RR = Red WW = White RW = Roan RW = the bull WW = the cow RW WW W roan white RW WW W roan white Set-up and Complete the Punnett Square just like a regular dominance.

Blood Types Sample Genotypes: Key Characteristics: Both alleles A and B are dominant, O is recessive Sample Genotypes Terminology Phenotype AA Homozygous A Type A AO Heterozygous A BB Homozygous B Type B BO Heterozygous B AB Heterozygous AB Type AB OO Homozygous Recessive Type O

O, A, B, or AB (universal donor) Blood Types Blood Type Genotype Can Receive Blood From Can Give Blood To A AA or AO A or O A or AB B BB or BO B or O B or AB AB AB, A, B, or O (universal acceptor) O OO O, A, B, or AB (universal donor)

Set-up and Complete the Punnett Square just like a regular dominance. Blood Type Practice Determine the possible genotypic and phenotypic ratios of the children born to a heterozygous mother (Type A) and a heterozygous father (Type B). parents A O AO = mom BO = dad AB BO B type AB type B Set-up and Complete the Punnett Square just like a regular dominance. AO OO O type A type O

In Hershey’s kisses, red and silver have incomplete dominance. RR R’R’ RR’

Incomplete Dominance Sample Genotypes: Key Characteristics: Two alleles share the dominance Capital letters are used to represent both dominant versions The heterozygous will show both in the phenotype equally, but they are blended together Sample Genotypes Terminology Phenotype BB Homozygous Dominant Dominant 1 BB’ Heterozygous Blend of 1 and 2 B’B’ Dominant 2

Incomplete Dominance Practice A horse can inherit the palomino color when they inherit both a brown (B) and a white (B’) allele. Show what would happen if a brown horse crossed with a palomino horse. genotypes parents B B BB = Brown B’B’ = White BB’ = Palomino BB = brown horse BB’ = palomino BB BB B brown brown BB’ BB’ B’ palomino palomino Set-up and Complete the Punnett Square just like a regular dominance.

X-linked Traits What happens when the traits for an organism are controlled by the genes located on the X chromosome? They are called X- linked traits. A human female carries 2 "X" chromosomes (XX). A male carries one "X" and one "Y" (XY).

X-linked Traits Key Characteristics: When a trait is X-linked it is ALWAYS connected to the X chromosome. NOTHING is written on the Y chromosome. If it is indicated as an X- linked trait, you must write the X chromosome and the dominant and recessive gene as a superscript.

X-linked Traits Sample Genotypes: Sample Genotypes Terminology Phenotype XAXA Homozygous Dominant Female Dominant Female XAXa Heterozygous Female (Carrier) XaXa Homozygous Recessive Female Recessive Female XAY Dominant Male XaY Recessive Male

X-linked Traits Practice In fruit flies, red eyes are dominant over white eyes. However, white eyes is an X-linked recessive trait carried by the female. What are the possible offspring of a carrier female and a red-eyed male? genotypes parents XR Xr XR = Red Xr = White XRXr = red carrier female XRY = red male XRXR XRXr XR red female red female XRY XrY Y red male white male Set-up and Complete the Punnett Square just like normal, but you must include the X chromosome.

More practice problems

Co-Dominance Practice In snapdragons, flower color is controlled by co-dominance. The two alleles are red (R) and white (W). The heterozygous genotype is expressed as red with white spots. A red and white-flowered plant is crossed with a white- flowered plant. What is the probability of producing a red and white-flowered plant? 2. In horses, brown (B) and white (W) are co- dominant. A white horse and a brown and white spotted horse were crossed. What is the probability of producing a white horse? 3. Jim has a brown horse and a brown and white spotted horse. His daughter, Lilly, really wants a white horse. Can Jim breed the two horses he has to produce a white horse for Lilly?

Blood Types Practice 4. Write the genotype for each person based on the description: a. Homozygous for type B b. Heterozygous for the A allele c. Type O d. Type A and had a Type O parent e. Type AB f. Blood can be donated to anybody g. Can only get blood from a Type O donor 5. Determine the possible genotypic and phenotypic ratios of the children born to a heterozygous mother with Type A blood and a heterozygous father with Type B blood. What percentage of the offspring will be able to donate blood to their mother?

Incomplete Dominance Practice 6. In parakeets, feather color is an incompletely dominant trait. You go to the pet store and find a clutch (group of baby birds) that is the following phenotypic ratios: 25% blue feathers, 50% green feathers, and 25% yellow feathers. What are the genotypes of the parent parakeets? Use a Punnett square to support your findings. 7. What would be the genotypic and phenotypic ratios if a blue parakeet was crossed with a green parakeet? 8. If a bird breeder wanted to have all green parakeets, what would be the best birds to breed? Use a Punnett square to support your answer.

X-linked Practice 9. Jenny and Steve are proud parents of a baby boy. They are wondering if their baby could be colorblind, a recessive, X-linked trait. Jenny is homozygous for normal vision and Steve is a colorblind male. Complete a Punnett Square to show the possibilities of their children.