Transcript Sex Linked Inheritance

Sex Linked Inheritance
Sex-Linked Inheritance
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Sex linked gene: a gene located on a sex
chromosome
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Genes found on the Y chromosome are found
only in males and are passed from father to son
Genes found on the X chromosome are found in
both sexes and can be passed from either parent
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Although X-linked diseases can occur in both sexes, they
usually occur in males (males only have one X
chromosome)
Sex linked Traits
Recessive
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Also called X-linked
recessive
Occurs when both matching
genes on the x chromosome
are abnormal to produce
disease.
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If only one X chromosome is
affected in a female, the
disease does not show up
If the X chromosome in a
male is abnormal, the male
will show the disorder
Dominant
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Also called X-linked
dominant or Y-linked
dominant
Occurs when the
abnormal gene dominants
(even when the matching
gene from the other
parent is normal).
Sex linked Traits
Recessive
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Examples
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Androgen Insensitivity
Syndrome
Color Blindness
Fragile X syndrome
Hemophilia
Muscular Dystrophy
X-linked anhidrotic
dysplasia
Dominant
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Examples
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Alport’s Syndrome
Aarskog’s Syndrome
Coffin-Lowry Syndrome
(CLS)
Rett Syndrome (RS)
Red-Green Color Blindness- found on the
X chromosome
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Presence in the Phenotype
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For this recessive allele to be expressed in females, it must be
present in two copies on both X chromosomes (thus it is
recessive)
To be expressed in males, it only needs to be present on the X
chromosome
How a normal
person might seem a
picture.
How a colorblind person might
see the same picture. The green
grass and the red flag stripes
appear to be the same color, as
do the greenish-blue sky and the
reddish-blue flagpole.
Color Blindness
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A female who carries
the gene for color
blindness mates with a
man who is not color
blind. How many of
their offspring will be
carriers of color
blindness? How many
of their children will be
color blind?
X’
X
Y
X
Muscular Dystrophy
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Show the potential
offspring for a given birth,
if the mother is a carrier
(only one abnormal X
chromosome) and the
father is normal:
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25% chance of a normal
boy
25% chance of a boy with
disease
25% chance of a normal girl
25% chance of a carrier girl
without disease
X’
X
Y
X
Muscular Dystrophy
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If the father has the
disease and the mother is
normal:
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100% chance of a normal
boy
100% chance of a carrier
girl without disease
X
X’
Y
X
Hemophilia
Hemophilia is a recessive sex linked trait.
Show the genotypes for an affected male
and an affected female. What would a
carrier of the disease look like?