Sex Chromosomes and

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Human
Genetics
Sex Chromosomes and Sex-Linked Inheritance
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Through research and the development of staining
techniques in the 1950's, scientists were for
the first time able to view the human
chromosome.
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Although they appear disorganized within the
cell, scientists have been able to identify and
number them from 1-22 in order of size.
This arrangement is called a Karyotype
The 23rd pair are the sex chromosomes.
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Chromosomes are sorted arranged into a 23
PAIR Karyotype for study..
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What makes us a BOY or a GIRL?
The recipe is in the last set of chromos..
Two X Chromos GIRL
X Y BOY
The sex chromosome X is inherited from the
mother. The father gives either an X (female) or
a Y (male). This is this chromosome
which determines the sex of the baby.
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The difference between BOYS and GIRLS...
..are found in sexual characteristics.
(Remember Phenotypes?..)
Secondary
Primary
genitals
body shape hips/pelvis/shoulders
muscle/fat distribution pear/apple
shape
testes/ovaries
sperm/egg formation
body size hands/stature
facial/body hair
voice characteristics
breast development females -gt 3 stages
males -gt 1 stage
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Why did Mother Nature put this silly looking
feather bouquet on my butt ?
In other animals, Secondary Sex Characteristics
may include
color/markings
antlers
I get it now!
decorative tail/appendages
scent glands
Miss Q.T. Peacock says Im attracted to men
with pretty feathers on their butt
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Remember how we found the probability of having a
boy or girl?
We can do a Punnett square just like we did with
other genes.
X
Y
50 Female 50 Male
X
XX
XY
X
XX
XY
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What do you notice when you look at these
chromosomes?
Two X Chromos GIRL
X Y BOY
The X chromosome is huge compared to the Y.
There are hundreds of other genes found on the X
chromosome. There are about 12 other genes on
the Y.
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The other genes found on the X chromosome can be
pretty important.
Some of the traits carried there are
hemophilia
Blood doesnt clot properly
Night blindness
color blindness
Duchenne's muscular dystrophy
Muscles get weaker and weaker
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Sex-linked inheritance

• We use a Punnett square to predict. Use the X
  and Y but add the letters to indicate the
  dominant and recessive traits on the X chromosome.

Use H for normal and h for hemophilia.
H h
H h
X X
X Y X Y
H H h h
X X X X
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