Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!sunybcs!joey!dmark
From: dmark@joey.cs.buffalo.edu (David Mark)
Newsgroups: sci.bio
Subject: Re: Question about Ferilization Genetics
Message-ID: <9613@eerie.acsu.Buffalo.EDU>
Date: 2 Sep 89 17:04:55 GMT
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Reply-To: dmark@joey.UUCP (David Mark)
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In article <5760@ttidca.TTI.COM> jackson@ttidca.tti.com (Dick Jackson) writes:
>My girlfriend and I had this big argument -- I am hoping that at least one
>good person in this group will help settle it.
>
>Its about the variability in offspring from the same parents.  I claimed
>that eggs and sperm from the same people contain identical genetic
>material and that variations in offspring occur because of semi-random
>combination when fertilization occurs.  She maintains that sperm and eggs
>are all different at the gene level.
>

For diploid species like us and many other higher animals, each sperm cell
contains exactly half of the genes of the ordinary cells of the male; 
however, it is a "more-or-less" random selection, one allele of each pair
of genes.  If there were 100 genes, there would be some 2^100 different
sperm cells.  And, there are way more than 100 genes!!  The same goes for
the eggs for diploid species.

Think about it.  If every spern cell from some male were identical, and
every egg from each female, then every monogamous couple that had
more than one child would have identical (except for age) children-- families
with male and female children would be evidence of non-monogamy!  

Honeybees and other bees, wasps, and ants are an interesting exception.
All males are haploid ("playing with a half set" of chromosomes) and so each
sperm from a particular male bee, wasp, or ant is identical.  But females
are diploid like us, and eggs are genetically different, with a 0.5 probability
of sharing any given gene.  Unfertilized eggs develop into males.  Thus male
bees, wasps and ants have neither fathers nor sons!  Brothers have a 50%
chance of sharing any specified gene, just as do full brothers in diploid
species.  But the queen bee mates once, and stores the sperm from one male in
her body, so sisters are 75% similar genetically, since the male half is
identical and the female half is 50% similar.  This is suggested as the
"reason" than so may hymenopterids have evolved colonial social structures
with female workers-- a female bee is more closely related to younger
sisters than she would be to her own offspring.  Thus, she maximizes the
probability that her genes will be represented in the next "generation" by
staying and helping mom raise more female offspring than by having offspring
of her own.  Stephen Jay Gould has an essay about this in one of his books.

David Mark
dmark@cs.buffalo.edu