Sex Determination: Male Heterogamety Video Lecture - NEET

[Music]
sex determination did you know that
nearly all tortoiseshell cats are female
we'll find out by later in this video we
are going to discover how sex is
determined human body cells have 46
chromosomes arranged in 23 pairs there
are 22 pairs of autosomes and one pair
of sex chromosomes or allo zones for a
male the sex chromosomes are usually XY
whilst for a female they are xx to make
a baby
a sperm has to join with an ovum or an
XL we looked at sperm and egg cells in
detail in this video you should know
that they only have half of the DNA of a
body cell they are haploid instead of 46
chromosomes so 23 pairs they just have
23 chromosomes in total 22 autosomes and
one sex chromosome or alisone an ovum
will always have an X chromosome but the
sperm will have an X or a Y if we looked
at this in a punnett square the gametes
from the female would always be X so X X
and the gametes from the male would be
either X or Y can you complete the
punnett square to show the probability
of having a male or a female child pause
the video complete the punnett square
and click Play when you're ready to
check did you get it right so the X from
the ovum and the X from the sperm would
produce a female baby and the X from the
ovum and the Y from the sperm would give
us a male child so really it is the man
who determines the gender of the child
he brings the Y which is the only chance
of a males child
unfortunately for an boylan a wife of
King Henry the 8th of England in the
16th century she was executed for not
providing a male heir to the throne
really he sperm were to blame from the
punnett square we would expect 50% of
the offspring to be male and 50% to be
female but the actual outcomes may be
different one couple could for example
end up with four goals discounting
social factors of such as sex selective
abortions at both the natural male to
female sex ratio for humans is about 105
males
to 100 females it is thought that this
is Nature's Way of overcoming the fact
that males have a higher risk of dying
younger than females the overall wold
male to female sex ratio drops down from
101 males - every 100 females so it is
closer to the expected 50% of each now
let's get back to our cat most
tortoiseshell cats are female because
this fur color is a characteristic found
on the X chromosome but males have One X
chromosome so why can't males be
tortoiseshell for a tortoiseshell cat
two X chromosomes are needed to show the
three different colors so as females
have X X 6 chromosomes they can be
tortoiseshell but X Y males can't now I
say most rather than all because you can
occasionally get a male tortoiseshell
cat just like you can occasionally get a
human man with X X chromosomes these
rare individuals have an extra strand of
DNA and so our X X Y rather than just X
Y so the male has the double X is needed
to be tortoiseshell there are other rare
chromosomal disorders that mean you can
have xx human males and ex-wife emails
or Turner syndrome when one sex
chromosome is present a solitary X XY Y
and double X double Y are two more
syndromes and they are many others from
this video you should know that females
usually
X X sex chromosomes and males usually
have XY the father provides the Y
chromosome and so the chance of having a
male child Falls and his shoulders if
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