Genetics help

Question

In the case of dalmation dogs, the non-spotted condition is recessive to the dominant spotted condition. Call the 2 alleles S for spotted and s for non-spotted. Both parents are heterozygous.  

A) what are the possible genotypes of the offspring? In what ratio do they occur? 

B) what are they possible phenotypes of the offspring? In what ratio do they occur ? 

 

2) consider again the case of the dalmation dogs. Say that a spotted and a non-spotted dog are crossed. Is it possible for them to produce any non-spotted puppies? Why or why not? Explain using a punnet square 

Answer 1

 First question:

 

P:                  S/s x S/s

 

 

Gametes: S and s for mother

 

                S and s for father

 

F1:    S/S, S/S, S/s, S/s and s/s

 

First three genotypes  would have spotted phenotype since it Spotted (S) is dominant: 75% spotted

 

Fourth genotype would be non-spotted phenotype as it is homozygous: s/s: 25% spotted

 

For second question genotype of non-spotted dog is s/s since it is homozygous. Spotted dog could be either S/S or S/S, you have not way to know ahead of time. Therefore, you design gametes for spotted dog as both heterozygous and homozygous for S and make two punnett squares using one genotype at time, the phenotypic ratio would differ based on genotype. You should be able to do it in the same way as I did above.