sex-influenced traits
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Sex-Influenced Traits. Male and Female Pattern Baldness. Where we are heading…. In the previous section, we learned about sex-linked traits that were controlled by alleles found on the sex-chromosomes. - PowerPoint PPT PresentationTRANSCRIPT
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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 alleles found on the sex-chromosomes.
In this section, we will discuss sex-influenced traits, traits that are controlled by alleles on 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 it’s 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 guy’s 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?Father’s genotype: bb X Mother’s 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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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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Let’s try a few problems involving sex influenced traits… 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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Let’s 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 parent’s genotypes? What are the genotypes and phenotypes of the children?
Let G represent no gout, and g represent gout.
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How about this one:
Rheumatoid arthritis occurs more often in females than males due to the presence of estrogen. A heterozygous woman marries a heterozygous male. RR would cause the condition in both sexes. A homozygous recessive, rr, genotype would prevent the disorder in both sexes