Name: __________________________________
2.21.07
1.
Comb shape in chickens is controlled by two genes and is a classic example of epistasis.
Remember epistasis? Epistasis is when the action of one gene controls the expression of another. Hair color in humans was the example given in class earlier today: any dominant allele of black/brown color (B_) would override the gene for red/blonde (R or r).
Remember, blondes and redheads only exist when the individual is homozygous recessive for the black/brown gene. In addition, epistatatic genes can be either dominant (B_, like human hair color) or recessive (aa, like albinism). As for the chickens, their combs are either walnut, pea, rose, or single. When crossing purebreds, the following ratios are always observed: single x single = all single walnut x walnut = all walnut rose x pea = all walnut
When we take the walnut birds from the above pea x rose cross we get the following ratios:
9/16 walnut
3/16 rose
3/16 pea
1/16 single
In addition, sometimes a non-purebred pea x rose cross will result in the following ratios:
1/4 walnut
1/4 rose
1/4 pea
1/4 single
What are the genotypes responsible for the four comb shapes in chickens? Show punnetts!

2.
Now that you’ve solved that, here’s another epistasis problem involving coat color in mice.
Agouti (gray) is dominant (G_), and black is recessive (gg). A purebred agouti was crossed with a pure white (albino) mouse of black parents. All of the offspring were agouti. Two of these agouti offspring were crossed, and the following ratios were obtained:
9/16 agouti
4/16 albino
3/16 black
What are the genotypes responsible for the three coat colors in mice? Show punnetts!
3.
In carrots, flower color can be yellow, green, or blue. The carrot itself may be long or short. As for flower color, the following crosses and ratios were always obtained: yellow x yellow = yellow blue x green = 1/2 blue and 1/2 green yellow x blue = green
As for shape, the following crosses and ratios were some of the potential results: long x short = 1/2 long 1/2 short long x short = all long long x long = all long short x short = all short
What would you have to cross with a short carrot with green flowers to get the following results?
103 yellow long, 101 green short, 99 yellow short, and 100 green long
Give phenotype, genotype, and show all punnetts, please.
4.
In rabbits, a series of multiple alleles controls coat color in the following way: C is dominant over all other alleles and causes normal color, while the chinchilla phenotype (light highlights) is created by c ch and is dominant over all alleles except C. The c h allele, dominant to only c a (albino), creates the Himalayan color pattern (black ears, white body).
Thus, the order of dominance is: C>c ch >c h >c a . The following crosses were obtained: a. Himilayan x Himilayan = albino and full color x albino = chinchilla. b. albino x chinchilla = albino and full color x albino = full color c. chinchilla x albino = Himilayan and full color x albino = Himilayan

For each of the above scenarios (a,b,c), determine genotypes of all rabbits involved as well as the results (genotype and phenotype) of a cross between the offspring from each pair of crosses (e.g. albino x chinchilla in scenario “a”).