Hey! Whats the best approach to this type of question?
Apparently the answer is E (12) but I dont get why. I thought the answer was D (9).
Thanks in advance! 
hi!
here they have not specified whether black colour is caused by a dominant or a recessive allele. so, let’s consider A= black coat colour and a= white coat colour.
Family R: we can see that the offsprings are equally black and white thus the black coat mouse has to be heterozygous for the trait(Aa).
Family Q: in family Q one mouse is heterozygous(Aa) but other can be AA or Aa as they both confer black coat colour but as in the question they are asking about the maximum possible number we will consider other mouse to be heterozygous(Aa) and offsprings also to be Aa.
Family P: same here we are crossing a heterozygous black mouse with a homozygous white mouse producing all heterozygous black mouse.
now we sum up all the heterozygous mouse in all three families including the two parents mouse then we will get 12 black heterozygous mouse.
Although the numbers might have been different if we consider black mouse to be homozygous(AA) and that can be a possibility but since they are asking for maximum possible number then we have to consider all black mouse to be heterozygous.
hope it helps.
you are absolutely right, thank you!
I have one question: can we consider, in family Q, that the other black mouse is Aa even if we see that in their offspring are not any mouse aa? (if we cross Aa with Aa, 25% is aa; but i cant see any white mouse)
Thank you so much for your time!
hi!
ya i got you what you are saying yes it can happen as heridity of a particular trait is completely based on chances so she has produced all black mouses till now maybe in other reproductive cycle she can have a white mouse(aa) so the expression of a particular trait is totally based on chnaces .
it might have been the case that all her offsprings be white.
hope you get it.
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Ohh got it!! Thank you so much!! 
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