Sex-influenced Traits

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Sex-influenced Traits
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• Previously, we learned about sex-linked traits,
  controlled by sex-chromosomes. (x-linked)
• We will now discuss sex-influenced traits,
  controlled by autosomal chromosomes

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What is a sex-influenced trait?

• A sex-influenced trait is controlled by a pair of
  alleles found on the autosomes. (Not on sex
  chromosomes)
• Its expression is influenced by gender (presence
  of hormones such as estrogen, progesterone,
  testosterone, etc.).
• Sex-influenced traits vary in the degree of the
  phenotypic expression.

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Example Pattern Baldness

• It can occur in both males and females, but is
  influenced by the hormone testosterone.

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The combination of alleles lead to different
phenotypic expressions depending on gender.
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What is the probability that you will be bald if
your father is homozygous and balding, and your
mother is homozygous and not balding?

• Father BB x Mother BB
• All offspring are BB
• If you are male, then you will
  be bald.
• If you are female, then you will not be bald.

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Actually, Its not that simple

• Many human traits are controlled
  by several different alleles and
  environmental factors. These
  traits are
  polygenic, such as
  height. (Actually the man at the
  right is a pituitary
  giant at 79
  due to an uncontrolled amount
  of
  growth hormone)
  
• This means that we cannot fully explain pattern
  baldness using sex-influenced inheritance. It is
  not easy to explain that diversity found in
  different ages of onset, as well as the severity
  of baldness.

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Another Example Singing voice

• The genotype that causes males to have a tenor
  voice (highest male singing voice), causes
  females to have a contralto voice (the deepest
  female singing voice).
• The genotype that causes males
  to have deep bass voices, is the
  same genotype that causes females
  to have high soprano voices.

Also
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Peacock plumage

• The plumage of a male peacock is highly
  decorated and colored, while the plumage of a
  female peahen is dull by comparison.

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A variety of peacock feathers