Gender at Conception
Name: Ronnie J.
I need to know if all embryos are girls at
conception. I overherd someone talking about this subject and i brought
up the fact that i thought that they were. Am I right or wrong?
Embryos are genotypically boy or girl from the time of conception, ie. the
chromosomes they inherit make them either XX-a girl or XY-a boy. However
they do not start to differentiate into sexes until about 6 weeks of
gestation. The gonads and tubes are undifferentiated at first and could
become either male or female. The Y chromosome provides instructions for
If the Y is present testosterone is produced and the
structures become male. Until recently it was believed that if the Y is not
present, the "default" phenotype occurs which is female. However, there is
some research that shows that there are triggers for female development as
No, all embryos are not female at conception. The egg recieves one sex
chromosome from the mother, and since the mother has two X chromosomes, the
egg will get one of these X chromosomes. At that point, it is neither male
nor female, just an unfertilized egg. When a sperm joins with the egg, it
will donate one sex chromosome -- either an X or a Y chromosome. The newly
concieved embryo will be a girl if the father's sperm cell donates an X,
embryo will be XX), and it will be a male if the sperm donates a Y (the
embryo will be XY). It's the luck of the draw whether the sperm that
fertilizes the egg has an X or Y chromosome in it from the father.
Assuming that you are talking about HUMAN embryos, then the answer is
no. The gender of the embryo is determined by one pair of chromosomes
-- XX for females, XY for males. An X chromosome is always inherited
from the mother, but the father may contribute either an X or a Y. Once
the egg and sperm unite, the gender is set.
For birds, it is females that have two different kinds of sex
chromosomes, and males that have two of the same kind.
For some species, like alligators, gender actually depends on the
temperature during early development.
So, nature has many answers to this question -- it depends on which
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Update: June 2012