Transcript Sex-linked Traits Traits

Sex-linked Traits
Traits (genes) located on the sex
chromosomes
Sex chromosomes are X and Y
XX genotype for females
XY genotype for males
Many sex-linked traits carried on
X chromosome
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Sex-linked Traits
Example: Eye color in fruit flies
Sex Chromosomes
fruit fly
eye color
XX chromosome - female
Xy chromosome - male
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Sex-linked Trait Problem
Example: Eye color in fruit flies
(red-eyed male) x (white-eyed female)
XRY
x
XrXr
Remember: the Y chromosome in males
does not carry the trait.
Xr
Xr
RR = red eyed
Rr = red eyed
R
X
rr = white eyed
XY = male
Y
XX = female
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Sex-linked Trait Solution:
Xr
XR
XR
Xr
Y
Xr Y
Xr
XR
Xr
Xr Y
50% red eyed
female
50% white eyed
male
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Pedigree Analysis
A Pedigree is a diagram of family
relationships.
In humans, controlled crosses cannot
be made, so geneticists often use
pedigrees to determine the mode of
inheritance (dominant, recessive, xlinked, etc.) of genetic diseases.
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Basic Pedigree Symbols
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Female Carriers
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Interpreting a Pedigree Chart
1. Determine if the pedigree chart shows an
autosomal or X-linked disease.
– If most of the males in the pedigree are
affected the disorder is X-linked
– If it is a 50/50 ratio between men and
women the disorder is autosomal.
Example of Pedigree Charts
 Is it Autosomal or X-linked?
Answer
 Autosomal
Interpreting a Pedigree Chart
2. Determine whether the disorder is
dominant or recessive.
– If the disorder is dominant, one of the
parents must have the disorder.
– If the disorder is recessive, neither
parent has to have the disorder because
they can be heterozygous.
Example of Pedigree Charts
 Dominant or Recessive?
Answer
 Dominant
Example of Pedigree Charts
 Dominant or Recessive?
Answer
 Recessive
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