Genes and Inheritance [3]: Sex Chromosome (High band Biology)
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Genes and Inheritance [3]: Sex Chromosome (High band Biology)


A Level Biology: Genes and Inheritance 3 – Sex
Chromosome Hi! Welcome to my third video in this series
about Genes. In this video, we are going to focus on the 23rd chromosome, which is the
sex chromosome. You probably remembered from the last video,
you get one of each chromosome from each parent. On the list of 23 that you have here, one
of these will have come from your mother and the other one will have come from your father
and the same with all of the chromosomes. The same is also true with the 23rd or the
X and Y chromosome. In this PowerPoint, this shows us the key
difference between the X and Y chromosome. What you will notice with the X is it is a
lot longer. It appears to have a lot more genetic information on the X chromosome than
there is on the Y. Like I said before, one of each chromosome
comes from each of your parents and the same is true with the 23rd chromosome or the sex
chromosome. This is the code that determines whether you are either a male or a female. In this case, XX is a female and XY is the
male. So therefore, if XX is the female, then the only chromosome that a female can give
across is the X and it is the male is the one that actually determines the sex of the
offspring. The male can either give across X or Y. It is in fact the male that determines
the sex of the offspring. This square diagram shows us the different
permutations that are possible. Down here, this represents the female and along here,
this represents the male. Obviously, these are the sperm and these are the eggs. What
you notice here is these are both X chromosomes because they are the long ones and hence,
sex of the offspring is female. This one, however, you have one X chromosome and one
Y chromosome, hence a male. Here as well, you have two X’s hence female and on this
one, an XY and therefore male. In the general population, there is an even
split of sperms carrying the X and carrying the Y chromosome. In reality, I think there
are more females on the planet than there are males. Generally speaking, there is an
even distribution of X-carrying sperm and Y-carrying sperm. You notice that all egg
cells must carry the X chromosome. It is on the Y chromosome that there is a gene that
basically determines that the embryo will turn into a male. If you receive 2 X chromosomes,
therefore, there is in this gene present and therefore the embryo continues to develop
as a female. In summary, the 23rd chromosome is the sex
chromosome. You get one chromosome from your mom and one for your dad. In the case of your
mother, she always donates the X chromosome. You father can either donate either the X
or the Y. In that respect, it is always the male sperm that determines the sex of the
baby. On the Y chromosome, there is a gene that causes the embryo to develop into a male.
If there is no Y chromosome present, this will cause the embryo to develop into a female. [end of audio – 03:37]
A Level Biology: Genes and Inheritance 3 – Sex Chromosome
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