Genetics: White & Black dog

[lakers2009]

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I read the answer but still don't get it. Any better explanation? Q: What genetic info can you deduce if cross a white male dog with a black female dog produces 1 black and 3 white puppies while crossing of the same male white dog with another black female dog results in 3 black and 1 white puppies? A: Both the black parents are recessive homozygotes if the white allele is dominant. Also both the black parents are heterozygotes if the white allele is recessive.

 

[jay47]

I read the answer but still don't get it. Any better explanation? Q: What genetic info can you deduce if cross a white male dog with a black female dog produces 1 black and 3 white puppies while crossing of the same male white dog with another black female dog results in 3 black and 1 white puppies? A: Both the black parents are recessive homozygotes if the white allele is dominant. Also both the black parents are heterozygotes if the white allele is recessive.

All you really need to know is that, for each cross, the male OR female is a heterozygote and the other one is a recessive homozygote.

All other conclusions don't make sense....

If either male or female in either cross was a homozygous dominant, you would ONLY get one color (assuming normal mendelian genetics, no partial/incomplete dominance etc...). The contra is also true. If both male and femal were recessive homozygotes, you would only get one color. If both male and female were heterozygotes, with one recessive and one dominant allele, then you should end up with a 50/50 ratio of black to white, which occurred in neither case. The probability of this would be slim compared to what did occur.