Sex Determination, pedigrees and
more
I. Sex Determination in Humans
A. General Information
1. 23 chromosomes come from Mom
2. 23 chromosomes come from Dad
3. 23rd pair of chrs. Is XX if ♀
4. 23rd pair of chrs. Is XY if ♂
★Total # of chrs. In normal human =
46
I. Non-sex chrs.
(autosomes)
2. Sex chrs.
B. Details of Sex determination
1. Having a Y chr. makes a ♂ child
2. Absence of an X chr. Is fatal
3. ♂s make X & Y sperm
B. Details of Sex determination
4. If X sperm fertilizes egg, then ♀ child
5. If Y sperm fertilizes egg, then ♂ child
★Therefore, ♂ determines the sex of the child
II. Pedigrees
A. = diagram showing the inheritance of a
certain gene throughbreeding
several generations
breeding
B. Symbols
♀
♂
offspring
III. Sex-linked traits
A. Usually found on X chromosome
B. Affects males more than females
C. Females can be carriers, & not have the
disorder (but can pass it to offspring)
D. Examples: color blindness and
hemophilia
IV. Hemophilia
A. Background Facts
1. Bleeding disorder
2. Caused by lack of clotting factor
3. Slight injury or nose-bleed can be fatal
IV. Hemophilia
4. Recessive sex-linked genetic disease
5. Info. on X chromosome (no info. On Y)
II. History
One of Victoria’s Secrets…
A. Queen Victoria of
England
was a carrier
of hemophilia
Victoria, age 16
II. History
II. History
Queen Victoria’s Family 1881
Queen Victoria’s descendants
Alexei Romanov,
son of Tsar Nicolas II
One of the most famous hemophiliacs was Russian Prince Tsarevitch
Alexei, killed along with all his family during the Russian revolution in
1917.
Treatment
A. Transfusions w/ clotting factor VIII
B. Danger:
HIV & other
blood-borne
pathogens
Hemophilia problem
Alice is a carrier
Her husband does not have the disorder.
Can their children have the disorder?
Yes!
Let’s use a Punnett square to determine the
probabilities.
X
Hemophilia problem
X
X
Xh
Y