SexInfluenced Traits

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Sex-Influenced Traits
Male and Female Pattern Baldness
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Where we are heading.

• In the previous section, we learned about
  sex-linked traits that were controlled by
  sex-chromosomes.
• In this section, we will discuss sex-influenced
  traits, traits that are controlled by autosomal
  chromosomes.

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What is a sex-influenced trait?

• A sex-influenced trait is a trait controlled by a
  pair of alleles found on the autosomal
  chromosomes (pairs 1 through 22) but its
  phenotypic expression is influenced by the
  presence of certain hormones.
• Sex-influenced traits can be seen in BOTH sexes,
  but will vary in frequency between the sexes, or
  in the degree of the phenotypic expression.

Estrogen, Progesterone, Testosterone, etc.
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Example of Sex-Influenced Traits

• Pattern Baldness
• Pattern Baldness can occur in both males and
  females, however it is much more common in males.
• Why is this?

Because the pattern baldness trait is influenced
by the hormone testosterone.
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Pattern Baldness

• The combination of alleles for pattern baldness
  will lead to different phenotypic expressions
  depending on the sex of the individual.
• For example Let B represent the non-bald
  allele- BB genotype non-bald in both sexes- bb
  genotype bald in both sexes- Bb genotype bald
  in men non-bald in females

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Pattern Baldness

• The B allele acts as a dominant allele in the
  heterozygous genotype in females, but acts as a
  recessive allele in the heterozygous genotype of
  the male.

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Pattern Baldness

• What would this bald guys genotype be?
• Bb or bb
• What about his balding mother?
• bb

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Try this out!

• What is the probability that YOU will be bald if
  your father is homozygous and balding, and your
  mother is homozygous and not balding?

Fathers genotype bb X Mothers genotype
BB All offspring are Bb If you are a male, you
will be bald! If you are a female, you will not
demonstrate pattern baldness.
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If only it were that simple!

• Hair is controlled by many different factors
  including several alleles and environmental
  factors. We will discuss this more when we study
  polygenic traits.
• This means that we cannot fully explain pattern
  baldness using sex-influenced inheritance. It is
  not easy to explain the diversity found in
  different ages of onset, as well as severity of
  baldness.

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Another example

• Singing voice!

The genotype that causes males to have a high
tenor voice causes females to have a deep
contralto voice. The genotype that causes males
to have deep bass voices is the same genotype
that causes females to have high soprano voices!
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How to solve sex-influenced problems using
dihybrid crosses

• Because the same genotype can produce two
  different phenotypes depending on the sex of the
  individual, when we solve sex-influenced problems
  we must use the alleles (bb) for the trait as
  well as the sex chromosomes (XY).

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How to solve sex-influenced problems using
dihybrid crosses

• Once we have determined our genotypes for both
  parents, we must FOIL them to find the different
  allele combinations.
• For example XXBBF-XB O-XB I-XB L-XB
• Then complete your dihybrid cross!
• OR

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You can solve using Monohybrid crosses

• Complete the simple cross and then express the
  phenotype based on whether we are talking about
  males or females.
• Ex. A heterozygous balding male reproduces with a
  heterozygous normal female.
• Do the cross and determine the phenotypic rations
  for males and females

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Lets try a few problems

• A male homozygous for clubfoot reproduces with a
  normal homozygous female. What are the genotypes
  and phenotypes of their children if testosterone
  alters the phenotypic expression of the trait in
  the heterozygous expression?
• Let F represent normal feet Let f represent
  clubfoot.

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Lets try a few problems

• Two heterozygous individuals get married and have
  lots of children. The father suffers with a
  painful condition called gout. What are the
  parents genotypes? What are the genotypes and
  phenotypes of the children?
• Let G represent no gout, and g represent gout.

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Here is the answer!