Transcript Sex-Linked Punnett Square Notes

Sex-Linked Punnett
Square Notes
Karyotype
A photograph of a cell’s
chromosomes arranged in
pairs according to size
Normal Karyotype: 23
pairs of chromosomes
•pairs 1-22 are
autosomes
• pair 23 are
sex
chromosomes
24-5
Sex Chromosomes
X
Y
X chromosome
• has over 1,000 genes
• most genes on the X
chromosome do not have
corresponding alleles on the
Y chromosome
Y chromosome
• has only a few dozen genes
• some genes are unique only
to the Y chromosome
Sex-Linked Traits
 Those
traits whose genes
are found on the X
chromosome but NOT on
the Y chromosome
Examples of Sex-linked Traits:
 Red-green
colorblindness
 Male Pattern Baldness
 Hemophilia (Queen
Victoria was a carrier)
 Duchenne Muscular
Dystrophy (fatal)
Color Blindness “tests”
The test below is simpler.
The individual with normal color vision will see a 5 revealed in the dot pattern.
An individual with Red/Green (the most common) color blindness will see
a 2 revealed in the dots.


Females = XX –carry 2
alleles for a sex-linked trait
Males = XY – only carry 1
allele for a sex-linked trait,
so it is easier for them to get
sex-linked diseases
Sex-Linked Traits, cont.

Males receive sex-linked
traits from their mother
because their mother gives
them the X chromosome
and their father gives them
the Y chromosome
Example of Sex-Linked Trait


H = Normal blood clotting
h = Hemophilia
Example of Sex-Linked Trait
 Normal male:
XHY
 Male with Hemophilia: XhY
 Normal female (not a carrier for
hemophilia – homozygous):
XHXH
HXh
X
 Normal female (carrier for
hemophilia – heterozygous):
 Female with Hemophilia: XhXh
Sample Problems
1.
H
h
X X
x
H
X Y
 Chances
of:
 a. hemophiliac
child? ¼ or 25%
XH
 b. hemophiliac
HXH
X
XH
son? 25%
 c. hemophiliac
HY
X
daughter? 0%
Y
 d. daughter
who is carrier? 25%
Xh
XHXh
XhY
2. A woman who is a carrier for
hemophilia marries a hemophiliac man.
 Chances
XHXh x XhY
of:
 a. hemophiliac
XH
child? 2/4 or 50%
HXh
X
h
X
 b. hemophiliac
son? 25%
HY
X
Y
 c. hemophiliac
daughter?
25%
Xh
XhXh
XhY
3. A normal man marries a Homozygous
normal woman.
XHXH x XHY
 Chances
of:
XH
 a. Will any of H XHXH
X
their kids be
hemophiliacs? Y XHY
0/4 or 0%
XH
XHXH
XHY
BLOOD TYPING


There are 3 alleles of the gene that
controls blood type: IA , IB , i The I
stands for immunoglobin.
IA and IB are Co-Dominant genes,
meaning when inherited together,
they are both fully expressed, not
blended, as in Incomplete
Dominance. “ i ” is the recessive
form of the allele.
Possible genotypes are as follows:
Genotypes
Blood type
IAIA or IAi
A
IBIB or IBi
B
IAIB
AB
ii
O
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Draw a Punnett square showing all
the possible genotypes for the
offspring produced by a type “O”
mother and a Type “AB” father.
Cross: ii x IAIB
IB