CHAPTER 12 SEX-LINKED TRAITS

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CHAPTER 12 SEX-LINKED TRAITS
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Karyotype a picture of chromosomes.
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Body Cells vs. Sex Cells

• Autosomes the first 22 homologous pairs of
  chromosomes.
• Autosomes are the same for both males and
  females.
• Sex cells Determine sex of offspring

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Is it Male or Female? Explain
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• Sex chromosomes determines the sex of the
  individual.

• The sex chromosomes are the 23rd pair of
  chromosomes. 
• XX female

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XYmale
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• Which parent determines the sex of an offspring?
• DAD
• Why?
• All moms have the genotype XX. When egg cells
  are made, they will all carry a single X
  chromosome.

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• All dads have the genotype XY. When sperm cells
  are made, 50 will have an X chromosome and 50
  will have a Y chromosome.
• Therefore, males and females are born in roughly
  a 5050 ratio.

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SEX-LINKED TRAITS

• Those traits that are controlled by genes on the
  X or Y chromosomes.
• NOTE The Y chromosome is much smaller than the X
  chromosome and only contains a few genes. Most
  sex-linked traits are on the X chromosome.

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In humans, hemophilia is a sex-linked trait. 
Having hemophilia is recessive (Xh) to being
normal (XH). The heterozygous female is called a
carrier.  Cross a carrier female with a normal
male.
__ XHXh __  X  __ XHY ___


XH XH
XH Xh
male
Xh Y
XH Y
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ResultsGenotypic ratio 1 XHXH 1 XHXh 1
XHY 1 Xh Y
Phenotypic ratio2 normal females 1normal male
1 male with hemophilia


XH XH Normal Female
XH Xh Normal Female
Xh Y Male w/ hemophilia
XH Y Normal Male
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Now You Try

• Cross a carrier female with a male with
  hemophilia.
• __ XHXh __  X  __ XhY ___

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ResultsGenotypic ratio 1 XHXh 1 XhXh 1
XHY 1 Xh Y
Phenotypic ratio1 normal female 1 female w/
Hemopholia 1normal male 1 male with
hemophilia


Xh Xh Female w/ hemophilia
XH XH Normal Female
Xh Y Male w/ hemophilia
XH Y Normal Male
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Genetic Sex-Linked Disorders Color Blindness

• Cause x-linked recessive
• 1/10 males have, 1/100 females have. Why the
  difference?
• Individuals are unable to distinguish shades of
  red-green.

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Genetic Sex-Linked Disorders

• 2- Hemophilia A and B
• Recessive disorders that affect 1 of 5,000
  males. These interfere with normal blood clotting
  and occur on the X chromosome.

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Polygenic Inheritance

• Traits that are influenced by several Genes.
• Show many degrees of variation.
• Examples
• Height
• Hair color
• Skin Color
• Eye Color