The role of mutation

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The role of mutation
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Substitution Mutation - Purifying Selection
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J. B. S. Haldane. 1947. The mutation rate of the
gene for haemophilia and its segregation ratios
in males and females. Ann. Eugen. 13262-271.
The primordial oocytes are mostly if not all
formed at birth, whereas spermatogonia go on
dividing throughout the sexual life of a male. So
if mutation is due to faulty copying of genes at
a nuclear division, we might expect it to be
commoner in males than females.
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J. B. S. Haldane. 1947. The mutation rate of the
gene for haemophilia and its segregation ratios
in males and females. Ann. Eugen. 13262-271.
we should expect higher mutability in the
male to be a general property of human and
perhaps other vertebrate genes.
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Because mammalian oogenesis differs fundamentally
from the process of spermatogenesis, the number
of germ-cell divisions from one generation to the
next in males, nm, is usually much larger than
that in females, nf.
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Number of divisions in females 24
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Number of divisions in males is age dependent.
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In mice, nm 57 and nf 28. In rats, nm 58
and nf 29.
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J. B. S. Haldane (1947) It is difficult to
see how this could be proved or disproved for
many years to come.
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Takashi Miyata (1987) Autosomal sequences are
carried one half of the time by females and one
half of the time by males. X-linked sequences
are carried two-thirds of the time by females and
one third of the time by males. Y-linked
sequences are only carried by males.
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Let um and uf be the mutation rates in males and
females, respectively, and a be the ratio of male
to female mutation rates. That is
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The zinc-finger protein-coding genes are a good
case for studying the ratio of male to female
mutation rates because in all mammals there are
two homologous genes, an X-linked one (Zfx) and
an Y-linked gene (Zfy). Shimmin et al. (1993)
sequenced the last intron of Zfx and Zfy genes in
human, orangutan, baboon, and squirrel monkey.
There are few functional constraints on introns
and, therefore, we may disregard selective forces
in this case. For all pairwise comparisons,
Shimmin et al. (1993) found that the Y sequences
were more divergent, i.e., have evolved faster,
than their X-linked homologues.
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The mean Y/X ratio was 2.25, which by using
translates into an estimate of ? 6.
Interestingly, the ratio nm/nf, is 200/33 ??6.
In rat, mouse, hamster, and fox, the mutation
rates in males were found to be twice as large as
those in females, which agrees with the nm/nf 2
ratio in these species.
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This phenomenon was dubbed MALE DRIVEN
EVOLUTION
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• Complication
• MALE DRIVEN EVOLUTION may be explained by two
  factors
• Mutation There are more mutations in males than
  in females.
• Selection Exposure of alleles to selection on
  hemizygous X chromosomes in males.

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How to separate sex from sex chromosomes?
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Ellegren and Fridolfsson (1997) studied rates of
mutation in birds. Male-to-female ratio in
mutation rates ranged from 4 to 7.
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The vast majority of mutations derive from the
male germline. Nothing happens, but if it does,
blame your husband.