Here are the answers to the guide questions: Q19. The genotype of the male is XcY (color-blind) Q20. The genotype of the female is XcX (carrier) Q21. The chance that the child will be color-blind is 50% Q22. The chance that a daughter will be color-blind is 0% Q23. The chance that a son will be color-blind is 100%

1. SEX-LINKED
TRAITS
Prepared by:
Luby G. Canobas

2. Sex-linked Traits
 is controlled by gene located on the X or
Y chromosome.
 Sex-linked traits are genetic
characteristics determined by genes,
which are located on sex chromosomes.

4. KEY POINTS
 Females have a homologous pair of X
chromosomes, whereas males have an
XY chromosome pair.
 The Y chromosome contains a small region of
similarity to the X chromosome so that they
can pair during meiosis, but the Y is much
shorter and contains many fewer genes.

5. The X and Y Chromosomes

6.  Males are said to be hemizygous because they
have only one allele for any X-
linked characteristic which makes the
descriptions of dominance and recessiveness
irrelevant for XY males.

7. Types of Sex-linked Traits
 Genes on the Y chromosomes are called
Y-linked genes.
 The few on the Y have to do with male-
only traits.
Example:
Hypertrichosis Pinnae Auris- it is a
genetic disorder in humans that causes
hairy ears.

8. Hypertrichosis Pinnae Auris
Since the only
humans who
have a Y
chromosome are
males, Y-linked
traits are passed
only from father
to son.

9. Types of Sex-linked Traits
 Genes located on the X chromosomes are
called X-linked genes.
 These are written with the X
chromosomes. If the gene is “linked” to
the X, then it is NOT on the Y.

10. Example of X-linked traits are:
- hemophilia
- color-blindness
- Duchenne Muscular Dystrophy

11. Hemophilia
 an X-linked genetically
inherited recessive disease in which one or
more of the normal blood clotting factors is
not produced.
 This results in prolonged bleeding from even
minor cuts and injuries. Swollen joints
caused by internal bleeding are a common
problem for hemophiliacs.
 Hemophilia most often afflicts males.

12.  In humans, hemophilia is a sex linked trait.
Females can be normal, carriers, or have the
disease. Males will either have the disease or
not (but they won’t ever be carriers)

13. Female Male
XH XH =Female, Normal XH Y = Male, Normal
XH Xh = Female, Carrier Xh Y = Male, Hemophiliac
Xh Xh = Female ,
Hemophiliac

14. SOLVE
 Show the cross of a man who has hemophilia with
a woman who is a carrier. What is the probability
that their children will have the disease?
__________
 A woman who is a carrier marries a normal man.
Show the cross. What is the probability that their
children will have hemophilia? What sex will a
child in the family with hemophilia be?

15.  A woman who has hemophilia marries a
normal man. How many of their children will
have hemophilia, and what is their sex?

16. Activity 5
Procedure:
1. Read the given problem:
a. Color-blindness is a recessive, sex-
linked disorder in humans. A color-blind man
has a child with a woman who is a carrier of
the disorder.

17. 2. Illustrate using a punnett square the
probability of having children who will have
normal vision and children who will be
color-blind.

18. Guide Questions:
Q19. What is the genotype of the male?
Q 20. What is the genotype of the female?
Q 21. What is the chance that the child will be
color-blind?
Q 22. What is the chance that a daughter will
be color-blind?
Q 23. What is the chance that a son will be
color-blind?

19. Genotype Phenotype
1. X X Normal Female
2. X Xc Normal Female Carrier
3. Xc Xc Color-blind Female
4. X Y Normal Male
5. Xc Y Color-blind Male