There are two different loci that cause white coat color in horses. One locus is the albino locus found in all mammals. Albinism
(c) is recessive and autosomal. Normal color is produced when at least one "C" is present. There is also a dominant white locus where Ww is a white horse, but WW is lethal. Normal color is produced when the genotype ww is present. An albino horse (ccww) is crossed to a white horse (CCWw). Half of the progeny from this cross are white, half are horses of other colors. If one selects from these progeny two white horses and crosses them, what ratio of living progeny (white to colored) is expected?
Answer: 6/12 are white, 3/12 are colored and 3/12 are albino.
Step-by-step explanation: If the horses are white and their parents are ccww (albino) and CCWw (white horse), according to Mendel's premises, they both must be CcWw, since the crossing provides one C from one parent and other c from the other parent, one W and the other w. Using Mendel's chess and the principle of independent segregation, the crossing between CcWw results in the following fenotypical ratio:
1/16 CCWW (lethal)
2/16 CCWw (white)
2/16 CcWW (lethal)
4/16 CcWw (white)
1/16 CCww (normal)
2/16 Ccww (normal)
2/16 ccWw (albino)
1/16 ccWW (lethal)
1/16 ccww (albino)
Excluding the 4 individuals that have the lethal locus, we have 6/12 that are white (2/12 + 4/12) and 3/12 (1/12 + 2/12) that are colored. Also, there are 3/12 of albino individuals as well.
