Transcript Sex-linked Traits and Disorders

Sex-linked Traits and
Disorders
• Some traits have their genes on the X or Y
chromosome.
• This is called a sex-linked gene because it
is on our sex determining chromosomes.
• The gene for color blindness is found on
the X chromosome.
What do you see
in the circle?
People with normal
vision will see a 6
People with red-green
color blindness will see
spots
http://www.colorvisiontesting.com/online%20test.htm
http://www.colbli
ndor.com/colorarrangementtest/
Click for answers
• It is a recessive disorder, you have to have
both recessive alleles to be color blind.
• However, males only have one X, so if
they get one copy, they are colorblind.
XX = normal female
XY = normal male
X*X = carrier female, normal vision
X*X* = color blind female
X*Y = color blind male
Try it:
• Cross a carrier female with a normal vision
male.
X*X
XY
Female genotype____
Male genotype ___
X*
X
X*X
X
XX
Offspring:
25% carrier F
25% normal F
Y
X*Y
XY
25% color blind M
25% normal M
What parents would make a color blind female?
• X*X mom and X*Y dad
X*
X
X*
Y
X*X*
X*Y
X*X
XY
Hemophilia is also sex-linked in humans.
• Hemophilia
is a
bleeding
disorder in
which it
takes a
long time
for blood to
clot.
http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001564/
• Females can be
normal (XX),
carriers (X*X), or
have hemophilia
(X*X*).
• Males can either
have it (X*Y) or
not (XY), they
cannot be a
carrier.
• Because hemophilia is sex-linked, it is
seen in males (1 in 10,000) more often
than in females (1 in 100,000,000).
Historical Connection: This disorder was seen in the British royal
family and a number of princes died at a young age due to the
disease.
http://www.sciencecases.org/hemo/hemo.asp
Try it: Cross a man with hemophilia
with a woman who is a carrier.
X*Y Female genotype ___
X*X
Male genotype ___
X*
Y
X*
X*X*
X*Y
X
X*X
XY
Offspring:
25% carrier F
0% normal F
25% hemophilia M
25% normal M
25% hemophilia F