The SRY gene is normally located on the human Y chromosome. This gene initiates the development of male characteristics.
Using this information, which of the following statements about the SRY gene is/are correct?
Insertion of the SRY gene into an X chromosome of a female zygote could give it male characteristics.
A sperm cell arising from incorrect division, which has a functional SRY gene, could give rise to a female with a sex chromosome trisomy following fertilisation with a normal ova.
During meiosis, crossing over could result in the formation of āXā sperm with the SRY gene, which could cause male characteristics after fertilisation.
my thinking is:
1 - is correct since itās logical
2 - is not correct since if a sperm has āa functional SRY geneā then it has a Y-chromosome, thus it wouldnāt be called female
3 - is correct since itās logical too
P.S. I checked and the answer is A, however now Iām questioning āif the 3rd statement is correct and it is possible to have a female with two X-chromosomes where one has a SRY gene, then it is also possible to get a female with trisomy XXX, where one X-chromosome has an SRY gene too(?) Then the 2nd statement should be correct too?ā
am I nuts or does it make sense, any thoughts on that will be appreciated
so non disjunction in the female ovum and crossing over of the sry gene from the y chromosome into the x, where the sperm carrying the x chromosome with the sry gene on it, would go on to fertilize the non disjunctioned egg, forming an X trisomy with an sry gene on one of them? i think that wouldnāt make statement 2 correct because it is stated that the sperm is the one that undergoes the division error, so it can either end up without any sex chromosomes and fertilize the egg which wouldnt be trisomy (it would be X monosomy; Turnerās), or have both X and Y together which like you said wouldnt be considered female (klinefelterās).
although the reason i looked up this question was because i am pretty sure i learned the X and Y chromosomes do not crossover because they are not homologous, after some research i found out that they rarely might, except itās exclusively in āpseudoautosomal regionsā these are regions that contain autosomal genes, so definitely not the male characteristics gene SRY. which make 3 incorrect. do you have any insight on this?
P.S for those with the same question, i looked into it a bit more and learned about a condition called XX male syndrome, where the paternal X chromosome carries the SRY gene after atypically crossing over along with the pseudoautosomal regions, so statement 3 definitely can happen.