Labrador retrievers may be black, brown, or golden in color. While each color may breed true, many different outcomes occur if numerous litters are examined from a variety of matings, where the parents are not necessarily true-breeding. The results below show some of the possibilities. Propose a mode of inheritance that consistent with these data, and indicate the corresponding genotypes of parents in each mating. Indicate as well the genotypes of the dogs that breed true for each color.
A: black x brown = all black
B: black x brown = ½ black, ½ brown
C: black x brown = ¾ black, ¼ golden
D: black x golden = all black
E: black x golden = 4/8 golden, 3/8 black, 1/8 brown
F: black x golden = 2/4 golden, ¼ black, ¼ brown
G: brown x brown = ¾ brown, ¼ golden
H: black x black = 9/16 black, 4/16 golden, 3/16 brown
To start to solve this problem we much first look at the clues presented.
- 3 variations (black, brown and golden) for one trait (coat color) which indicates either co-dominance/incomplete dominance or a multi-gene trait
-the phenotype ratios with a 16 as a denominator is a dead give away that this is a two gene trait
Now we have two genes ...
Explanation of how to decipher allele and gene relations in dog coat color example with Punnett squares to explain all test crosses.