sex-linked punnett. karyotype a photograph of a cell’s chromosomes arranged in pairs according to...
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Sex-Linked Punnett
KaryotypeA 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 TraitsThose traits whose genes
are found on the X chromosome but NOT on the Y chromosome
Examples of Sex-linked Traits:
Red-green colorblindnessMale Pattern BaldnessHemophilia (Queen Victoria was a carrier)
Duchenne Muscular Dystrophy (fatal)
Color Blindness “tests”
The test to the left 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.
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
Genotypes Phenotypes HH Normal Hh Normal/Carrier hh Hemophilia
Example of Sex-Linked TraitNormal male:Male with Hemophilia:Normal female (not a carrier for
hemophilia – homozygous): Normal female (carrier for
hemophilia – heterozygous): Female with Hemophilia:
XHY
XhY
XHXH
XhXh
XHXh
Sample Problems
1. XHXh x XHYChances of:a. hemophiliac
child? b. hemophiliac
son? c. hemophiliac
daughter? d. daughter
who is carrier?
XHXH
XH
YXhY
XHXh
XH
Y
XH Xh¼ or 25%
½ or 50%
0%
½ or 50%
2. A woman who is a carrier for hemophilia marries a hemophiliac man.
Chances of:a. hemophiliac
child? b. hemophiliac
son? c. hemophiliac
daughter?
XHXh
XH
YXhY
XhXh
Xh
Y
XH Xh
2/4 or 50%
½ or 50%
½ or 50%
XHXh x XhY
3. A normal man marries a Homozygous normal woman.
Chances of: a. Will any of
their kids be hemophiliacs?
XHXH
XH
YXHY
XHXHXH
Y
XH XH
0/4 or 0%
XHXH x XHY
A normal woman (whose father is a hemophiliac) marries a hemophiliac man.
What are their genotypes?
XHX? XhY
Her dad - XhY
XHXh and XhY