The document discusses sex-linked traits which are traits controlled by genes on the sex chromosomes. It notes that females have two X chromosomes and are denoted XX while males have one X and one Y chromosome and are denoted XY. The X chromosome contains many more genes than the Y chromosome. It describes an experiment by Thomas Hunt Morgan which showed that eye color in fruit flies is sex-linked. It then explains that sex-linked disorders mainly affect males because females need two copies of a recessive gene while males only need one. It gives color blindness as an example and notes that carrier females have one normal and one recessive gene.

1. Notes: Sex-Linked Traits (pg 16)

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

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.