Suppose that 2 alleles on 1 homologous chromosome are A &B &the other homologous chromosomes alleles are a &b?

Question

How many different genetic types of gametes would be produced without crossing over?
What are the genotypes of the gametes?
If crossing over were to occur, how many different genetic types of gametes could occur?
List them..

Answer 1

"Without crossing over" means that the alleles on one chromosome are stuck with each other and have to go into the same gamete together. In that case, there are only two kinds of gametes possible for these particular traits: AB and ab.

"With crossing over" means that the homologous chromosomes traded a segment while they were synapsed. The trick is that the two chromatids that were touching, the inner ones, did the trading. The two outer chromatids were not touching or synapsing, and they did no trading. So you have two unchanged chromatids that produce gametes just like the original or parental types: AB and ab. And you have chromatids that have traded parts. Assuming that they traded a section with one of the genes in the problem, these two gametes have a recombination of alleles: Ab and aB. There are four different kinds of gametes produced with crossing over: AB, ab, Ab, aB.