Mar
14
Genetics: Interactions of genes at multiple loci?
ByWhen a yellow female Labrador retriever was mated with a brown male, half the puppies were brown and half were yellow. The same female, when mated with a different brown male, produced only brown offspring. Explain these results.
2 Comments
March 14th, 2011 at 1:26 am
Let B = Brown and b = yellow (since B is dominant and b is recessive)
First cross with yellow female with brown male produced
1/2 BB or Bb (could be either since the brown offsprings could have been heterozygous)
1/2 bb (has be to so because yellow alleles are recessive)
Second cross with yellow female and brown male produced
Bb (cannot be BB since the female does not have a B allele)
Therefore, we know that the first brown male dog was heterozygous. If the first dog was homozygous, the cross would not have been able to produce any yellow offspring.
March 14th, 2011 at 2:11 am
Here yellow coluor is recessive and brown is dominant. so lets assume that a yellow female has a genotype yy.
In first case, the genotype of male would be Yy (brown colour), so after mating
yy X Yy
the genotype of offsprings would be Yy (brown), Yy (brown), yy (yellow), yy (yellow). so 50% offsprings are yellow and 50% are brown.
In second casr, the genotype of brown male would be YY (homozygous dominant), so after mating
yy X YY
the genotype of offsprings would be Yy (brown), Yy (brown), Yy (brown), Yy (brown). so all are brown