Question

A tropical fish fancier produced an albino zebra fish (fish #1). This fish lacked the blue stripes characterisitics of a normal zebra fish. When he crossed a normal zebra fish (fish #2) with fish #1 all the offspring were normal. When he crossed two of the normal offspring (fish #3 and fish #4) 1/4 of the offspring were albino and 3/4 were normal. He then crossed an albino (fish #5) to fish #3 and 1/2 were normal and 1/2 were albino. What are the genotypes for all the numbered fish mentioned in this problem?

Answer 1

Fish number 1 has two recessive alleles, possibly for a gene for the stripe colour. I say this because crossing this to a normal produces normal offspring (let's call them the F1 offspring) which, when crossed have 1/4 albino. This suggests that the F1 offspring each carry a recessive allele:



This must have come from the original cross which I'll illustrate the possible genotypes:



I'll leave you to carry on with this question but if you have any problems let me know - I'll check back later.

Answer 2

thanks so much could you finish answering the question because im preparing for a test and i want to make sure i have the question answered completely so i will be able to review and study the answers your provided

Answer 3

I think I've given you the genotypes of fishes 1,2 3 and 4; fish 5 must have a homozygous recessive genotype - this is shown as "ss" in the above scheme where "S" is the normal, dominant allele, "s" is the mutant allele.