Question

Why do sister chromatids on any replicated chromosome above possess the same allele – AA or aa, but not Aa? BB or bb, but not B b?

Answer 1

The genes are occured in paires are called alleles,which located each chromosome.(like for a paricular trait the alleles are present on sister chromatids)

let us take an example allele A on one chromatid and a on second chromatid(sister).Then(the seperation of the chromatids happends -in anapahse of mitosis)if the replication of chromatid happends then the one newly formed strand of chromosome have the same replica of the allele.That if it have allele A ,then the newly synthesised one also have A ,then in case of strand with 'a' also.