The only exception is the sex chromosome pair known as Z and W. All male pigeons will have two Zchromosomes and every hen a combination of one Z and one W. We know that the Zchromosome carries many different gene locus points while a W Chromosome doesn't seem to have any genes.
W and Z. The W is very small and only found on a hen along with one Z while a cock has two Zs making up his sex chromosome pair and both Z's will be large with a large number of assigned genes.
When the female is the homogametic member the symbol X is used for her large sex chromosome or X//X set while Z is used when it is the male that carries the two large sex chromosomes or Z//Z set.
Other organisms have mirror image sex chromosomes: the female is "XY" and the male is "XX", but by convention biologists call a "female Y" a W chromosome and the other a Zchromosome.
The human Y chromosome is unable to recombine with the X chromosome, except for small pieces of pseudoautosomal regions at the telomeres (which comprise about 5% of the chromosome's length).
When chromosome surveys were first done in the 1960s, it was reported that a higher than expected number of men in prisons were found to have an extra Y chromosome, so that for a while it was thought to predispose a boy to antisocial behavior (and was dubbed the "criminal karyotype").
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