MadSci Network: Genetics

Re: Can XYY males produce gametes containing YY or XY?

Date: Sat Oct 30 13:31:53 2004
Posted By: Paul Szauter, Staff, Mouse Genome Informatics
Area of science: Genetics
ID: 1098527448.Ge

It is hard to find a good answer for this question. In general, meiosis in a
trisomic individual 
results in "trivalent" formation during meiosis I, with two of the chromosomes
paired for part of 
their length and the third possibly paired with another part of one of the two
chromosomes. Because the pseudoautosomal region shared between the X and Y is
rather small, 
it is difficult to see how the XYY trivalent would form. This would leave a
univalent Y 
chromosome in XYY male meiosis. There are various consequences of having an
chromosome in meiosis. Often it is lost; sometimes, the chromosome segregates to
one pole as 
a univalent at meiosis I. In this case, there would be a higher incidence of XYY
males among the 
sons of XYY males.

XYY males arise from normal fathers by nondisjunction at the second meiotic
division, which is 
rather rare. From an XYY father, YY sperm would arise from segregation of the
univalent to one 
of the poles.

It is not easy for a univalent to segregate to one of the poles, because the
mechanism for 
orienting a chromosome pair (a bivalent) at meiosis I requires the opposite
orientation of 
homologous kinetochores. This is not possible with a univalent.

The guess in Griffiths et al. is a good guess, if that is what it is; I can't
find a good citation 
detailing the incidence of XYY sons from XYY fathers.

Fertility of XYY males is somewhat impaired. There seems to be some mechanism
for keeping 
gametes from meioses with unpaired chromosomes from developing normally.

Of course, even if the univalent is always lost, it is possible for an XYY
father to have an XYY son 
by the normal mechanism of nondisjunction at the second meiotic division.

With XXY individuals, trivalent formation is more likely, because the two X
chromosomes can pair 
outside of the pseudoautosomal region.

From the web:


"Individuals with 47,XYY may have hypospadias, small testicles, and undescended
(Buyse, 1990), and there may be an association with renal agenesis and renal
cystic dysplasia 
(Rudnik-Schoneborn et al., 1996)."

Buyse ME, ed. Chromosome X, Chromosome XYY. In:
Birth Defects Encyclopedia. Cambridge, Massachusetts:
Blackwell Scientific Publications, 1990:400-401.


Here is a good summary on the web:



Paul Szauter
Mouse Genome Informatics

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