SexLinked Traits Traits controlled by a gene found on the sex chromosome The Y chromosome is shorter than X therefore some genes on the X chromosome may be missing from Y Sexlinked disease is less likely to affect females because they have 2 X chromosomes ID: 920949
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Slide1
28N
Sex-Linked Traits
Slide2Sex-Linked TraitsTraits controlled by a gene found on the sex chromosomeThe Y chromosome is shorter than X; therefore, some genes on the X chromosome may be missing from Y
Sex-linked disease is less likely to affect females because they have 2 X chromosomes
Slide3Sex-Linked TraitsCarrier = an individual who is heterozygous for a recessive, disease-causing allele. The carrier of the allele usually shows no symptoms of the disease but can pass the defective allele on to his or her children.Females can be carriers of sex-linked traits because they can be heterozygous for the recessive trait
Slide4Sex-Linked TraitsExample 1: Colorblindness = can’t tell the difference between red and greenCaused by a defective allele
C = not colorblind c = colorblind
Slide5Sex-Linked TraitsCross a normal vision female with a colorblind male
Phenotype Ratio:
50% female carrier of colorblindness50% normal vision male
X
X
C
X
C
Y
X
C
X
X
C
X
X
C
Y
c
c
c
X
C
Y
Slide6Sex-Linked TraitsExample 2: Hemophilia = the person’s blood is unable to clot and bleeding will not stop
H = does not have hemophilia h = has hemophilia
Slide7Sex-Linked TraitsCross a female carrier of hemophilia with a hemophiliac man
X
X
X
H
Y
X
H
X
X X
X
H
Y
h
h
h
h
h
h
X Y
Phenotype Ratio:
25% female carrier of hemophilia
25% hemophiliac female
25% normal male
25% hemophiliac male
Slide8Sex-Linked TraitsExample 3: Male BaldnessCross a normal female with a bald male
B = not bald b = bald
X
X
B
X
B
Y
X
B
X
X
B
X
X
B
Y
b
b
b
X
B
Y
Phenotype Ratio:
50% female carrier of baldness
50% normal male