Sex-linked Traits and Disorders

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Sex-linked Traits and Disorders
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• Some traits have their genes on the X or Y
  chromosome.

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• This is called a sex-linked gene because it is on
  our sex determining chromosomes.

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• 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/online20test.ht
m
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http//www.colblindor.com/color-arrangement-test/
Click for answers
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• 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 XX carrier
female, normal vision XX color blind
female XY color blind male
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Try it

• Cross a carrier female with a normal vision male.
• Female genotype____ Male genotype ___

XX
XY
X
X
Offspring 25 carrier F 25 normal F 25 color
blind M 25 normal M
X
XX
XX
XY
Y
XY
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What parents would make a color blind female?

• XX mom and XY dad

Y
X
X
XY
XX
XY
XX
X
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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/PMH000156
4/
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• Females can be normal (XX), carriers (XX), or
  have hemophilia (XX).
• Males can either have it (XY) or not (XY), they
  cannot be a carrier.

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• Because hemophilia is sex-linked, it is seen in
  males (1 in 10,000) more often than in females (1
  in 100,000,000).

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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.
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Try it Cross a man with hemophilia with a woman
who is a carrier.

• Male genotype ___ Female genotype ___

XY
XX
Y
X
Offspring 25 carrier F 0 normal F 25
hemophilia M 25 normal M 25 hemophilia F
X
XY
XX
XY
XX
X
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• http//faculty.clintoncc.suny.edu/faculty/michael.
  gregory/files/bio20101/Bio2010120Laboratory/Ped
  igree20Analysis/PEDIGREE.HTM
• Pedigree worksheet

http//biology.clc.uc.edu/courses/bio105/sex-link.
htm