OK, I was a bit rushed in writing and did not state the x
and y chromosome part quite correctly.
But you are absolutely wrong when you state that a man's
x-sperm are all alike and his y-sperm are all alike. You
are leaving out the "shuffling" that takes place between
*all* the other chromosome pairs except for the x and y.
Only the x chromosomes in the "x-sperm" are alike, and the
y-chromosomes in the "y-sperm". But *all* the other 22
chromosomes are most likely unique. Each pair of
chromosomes in the sexual cells swaps bits and pieces of the
chromosomes *before* they separate and the sperm cells are
formed with one-each of the 22 chromosomes and either an x
or a y chromosome. Same goes for the 23 pairs that the
female has - they swap pieces before separating to form the
egg cells. (I'm skipping a couple of details here). So
there is perhaps *slightly* more variability from the female
side than the male, but I'd hardly think that the ratio of
23 to 22 is terribly significant.
But to get somewhat back on-topic: a male's ancestry can be
compared with another male's, since the y chromosome, except
for mutations, *is* unchanged. So if you are a descendant
in the male line from some ancestor, you will have the exact
same y chromosome as all other male-line descendants of the
same ancestor. Trouble is, this doesn't eliminate
possibilities like a *different* male descendant having been
the father of a child somewhere along the line. Like: was
it Thomas Jefferson or his brother's son(s) who fathered
Sally Hemmings' children - no way to tell from the genes.
There are also some other things in human cells that get
passed from generation to generation. These are called
mitochondria or mitrochondrial DNA. They are handed down
*only* in the egg cell from the mother, and also don't
change except for mutations. So men never pass them on.
But the mitrochondrial DNA can be compared with anyone
else's who is also descended in the *female* line (except
for the last generation, which may be female > male) from a
common ancestor.
Ruth Ann
J & K Sindberg wrote:
Sex? I was not discussing sex. I was discussing why
children in a family, regardless of their sex, usually
all look different, because each of their mother's
eggs are different.
You are wrong writing that we have 22 chromosome pairs
plus either an x or y chromosome. We all have 23 pairs.
One of each pair coming from the mother and the other
from the father. In the case of males, one pair contains
sex determining abilities, the xy pair (x=female, y=male).
The female's sex determining chromosome is an xx pair.
But unlike the male's it can not also determine sex of
future generations, since it has no male parts.
In the following I may be incorrect. If so, please offer
correction(s):
When sperm are created, the male's pairs are separated,
making female and male producing sperm, each with a single
set of 23 chromosomes. Likewise the female's eggs also
have a single set of 23 chromosomes. They are created
by combining the 23 pairs, resulting in a unique new single
set of 23 chromosomes. It is not a copy of one or the
other of her pairs. In other words while a man's x-sperm
are all alike and his y-sperm are all alike, with a women
generally each of her eggs is different.
Y-chromosomes are the same generation after generation.
X--chromosomes are recombinations, generation after
generation. The father determines the child's sex.
The mother provides the non sex differences, the
unigueness, among her children. Both past down
their genes.
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