Transcript Sex-linked traits - Sonoma Valley High School

Chromosomes and inheritance
Sex
determination
– Female and
males have same
autosomes.
– Females have
“XX” for sex
chromosomes.
• Gametes only X
– Males have “XY”
for sex
chromosomes.
• Gametes x or y
X
X
X
XX
XX
Y
XY
XY
Sex Linked Traits
• Sex linked traits are
located on the X sex
chromosome.
• Males:
– XR Y
– XrY
• Females:
– XR XR
– XR Xr
– XrXr
Males: ½ chance of
recessive phenotype
Females: 1/3 chance of
recessive phenotype
Cross a carrier female for white eyes with a
male that is white eye. What percent of the
offspring will have white eye?
Xr
Y
XR
XRXr
XR Y
Xr
Xr Xr
Xr Y
P = XRXr x XrY
Multiple Alleles
• Instead of
two versions
or alleles
there are 3
or more
alleles.
•
•IA, IB, i are the
alleles for blood
type.
•Possible
genotypes would
be
–IA IA, Iai
–IB IB , IBi
–IA IB
–ii
White board:
What blood types might result in a family in
which the mother is O and the father is AB?
i
i
IA
IA
i
IA
i
•P = IAIB x ii
50% A, 50%B
IB
IB
i
IB
i
Chromosome Mutations
• Germ cell mutations
– Occurs in cells that
will become sperm or
eggs
• Somatic mutations
– Occurs in body cells.
Chromosome Mutation:
deletion
• When a portion
of the
chromosome is
lost.
Chromosome Mutations:
inversion
• occurs when a piece
of the chromosome
detaches and then
reattaches in the
opposite position.
Chromosome Mutations :
translocation
• When a part of
a chromosome
breaks off and
reattaches to
another
chromosome.
Chromosome
Mutations:
Nondisjunction
• When chromosomes do
not segregate properly
during meiosis.
• Nondisjunction results
in missing or extra
chromosomes
Disorders Due to Nondisjunction
• Trisomy means 3
chromosomes
instead of normal
pair.
• Monosomy means
1 chromosome
instead of normal
pair.
Review
1. For a sex-linked trait
what are the odds that
a male will have the
recessive phenotype?
2. What happens with
deletion?
3. Think back to the
karyotyping lab.
Name a disorder that
can occur due to
trysomy.
Answers:
1. ½
2. A portion of a chromosome is lost.
3. Downs syndrome, or Edward’s
syndrome, or Turner’s syndrome…