Y Chromosome Evolution
Country: United States
Date: September 2006
If males carry the x and y chromosomes and the
female only carries the X, doesn't it make it more clear that males
where first? In order ror the first to duplicate or make another it
would need the same or of the same to duplicate. If there was only
X chromosomes then there would be no males; with male being first
you have the ability to produce female or male.
Not all organisms use the X Y system. For example in birds the female is
the one who is heterogametic (different sex chromosomes). In "lower"
mammals the sex chromosomes are more equal in size. It appears that over
evolutionary time, one of the sex chromosomes started losing genetic
material to the other chromosome during unequal crossover. The main gene on
the Y that determines maleness is the SRY and as long as it remains on the
Y, this chromosome will be the one that determines maleness, at least in
Your theory does not explain sex determination in birds. Males are XX (or
ZZ) and females are XY (or ZW).
Ron Baker, Ph.D.
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Update: June 2012