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Title: Does crossing over occur in sex chromosomes, X and Y? Post by: ParameciumHairs on Nov 23, 2016 Meosis creates gametes. In humans, these are egg and sperm. So why is it that there are male and female chromosomes (from each parent) crossing over in meosis? This makes no sense, and I think I have been missing something major for years. This seems like a chicken and the egg scenario. :-\
I hope you understand what I mean and can help me out. lol Title: Does crossing over occur in sex chromosomes, X and Y? Post by: bio_man on Nov 24, 2016 Excellent question
They do cross over in certain regions called pseudoautosomal regions. The pseudoautosomal regions, PAR1, PAR2, and PAR3, are homologous sequences of nucleotides on the X and Y chromosomes. Although genetic recombination (occurring during sexual reproduction) is known to be limited only to the pseudoautosomal regions (PAR1 and PAR2) of the X and Y chromosomes, a 2013 study reports allelic unequal recombination between the X-chromosome-transposed region (XTR) Yp11.2 and Xq21.3, indicating the presence of a new PAR, which has been named PAR3. This PAR3 region is exhibited in 2% of the general population. Also, the additional layer of justification has been provided from another study on six dyslexic cases[4] which were shown to harbor duplications and deletions in the same Xq21.3 and Yp11.2 regions through allelic unequal recombination. |