2. Notes: Sex-Linked Traits (pg 16)
• Sex-Linked Trait = Traits controlled by genes
located on sex chromosomes
3. Notes: Sex-Linked Traits (pg 16)
• Sex-Linked Trait = Traits controlled by genes
located on sex chromosomes
• Females = XX, Males = XY
4. Notes: Sex-Linked Traits (pg 16)
• Sex-Linked Trait = Traits controlled by genes
located on sex chromosomes
• Females = XX, Males = XY
• The X chromosome is large and contains about
2000 genes. The Y chromosome is very small
and has only86genes.
5. Notes: Sex-Linked Traits (pg 16)
• Sex-Linked Trait = Traits controlled by genes
located on sex chromosomes
• Females = XX, Males = XY
• The X chromosome is large and contains about
2000 genes. The Y chromosome is very small
and has only86genes.
• Genotypes written as XAXA (females) and XAY
(males)
6. • Discovered by Thomas Hunt Morgan in 1907
while studying fruit flies
7. • Discovered by Thomas Hunt Morgan in 1907
while studying fruit flies
• He crossed a white-eyed female (XrXr) with a
red eyed male (XRY)
8. • Discovered by Thomas Hunt Morgan in 1907
while studying fruit flies
• He crossed a white-eyed female (XrXr) with a
red eyed male (XRY)
XrXr
XR
Y
9. • Discovered by Thomas Hunt Morgan in 1907
while studying fruit flies
• He crossed a white-eyed female (XrXr) with a
red eyed male (XRY)
XrXr
XR Xr X RX r
XR
X rY XrY
Y
10. • Discovered by Thomas Hunt Morgan in 1907
while studying fruit flies
• He crossed a white-eyed female (XrXr) with a
red eyed male (XRY)
XrXr
XR Xr X RX r Females: 100%
XR Red eyed
Males: 100%
X rY XrY White eyed
Y
11. Sex-Linked Disorders
• Males are more likely to be affected, because
females must inherit 2 bad copies of a gene to
be affected, while males only need 1 bad copy
12. Sex-Linked Disorders
• Males are more likely to be affected, because
females must inherit 2 bad copies of a gene to
be affected, while males only need 1 bad copy
• Example: Color Blindness (b) is recessive to
normal vision (B). Color blind female = XbXb
Color blind male = XbY
13. Sex-Linked Disorders
• Males are more likely to be affected, because
females must inherit 2 bad copies of a gene to
be affected, while males only need 1 bad copy
• Example: Color Blindness (b) is recessive to
normal vision (B). Color blind female = XbXb
Color blind male = XbY
• A woman who is XBXb is called a carrier: she
has normal vision, but can have colorblind
children
14.
15.
16. Sex-Linked Disorders
• Males are more likely to be affected, because
females must inherit 2 bad copies of a gene to be
affected, while males only need 1 bad copy
• Example: Color Blindness (b) is recessive to
normal vision (B). Color blind female = XbXb Color
blind male = XbY
• A woman who is XBXb is called a carrier: she has
normal vision, but can have colorblind children
• Other sex-linked disorders: Hemophilia, muscular
dystrophy, baldness
17. Output (pg 17)
Practice Problem 1
Hemophilia is a recessive sex-linked disease. A
woman who is a carrier for hemophilia (XHXh)
has a child with a normal man (XHY). Draw the
Punnett square and give the phenotype ratios
for males and females separately.
18. Output (pg 17)
Practice Problem 2
A woman who is a carrier for hemophilia has a
child with a man who has hemophilia.