school purposes

1. F. Sex Linkage
Subject: Genetics

2. 1. X-linkage inheritance
X-linked recessive inheritance is a way a genetic
trait or condition can be passed down from parent
to child through mutations (changes) in a gene on
the X chromosome. In males (who only have one
X chromosome), a mutation in the copy of the gene
on the single X chromosome causes the condition.

3. X- linked inheritance
Ex.
Female has two X chromosomes, she may either be
homozygous or heterozygous for and X-linked gene,
Male having only one X-chromosome is said to be
hemizygous.
Example: of X-linked inheritance in Drosophila and
humans are as follows:

4. 1.1 white-eye mutant in Drosophila melanogaster

6. 1.2 Hemophilia in humans
• The gene for hemophilia is located in the X chromosome. It is
recessive and its expression is completely masked by the
dominant allele. Hence, a woman heterozygous for the gene h
is capable of transmitting the trait to half her son, herself not
showing any visible effects of the gene h.

9. Table 4-1. shows the list of additional example of X-linked traits
in humans.
Table 4-1. Some X-linked characteristics in humans.
1. Color-blindness
2. Muscular dystrophy
3. Hemophilia
4. Glucose-6-P dehydrogenase deficiency
5. Hypochromic anemia
6. Congenital deafness
7. Mental deficiency
8. Parkinsonism
9. Ocular albinism
10. External opthalmoplegia and myopia
11. Congenital cataract
12. Stationary night blindness with myopia
13. Retinitis pigmentosa
14. Albinism-deafness syndrome

10. • 15. Congenital adrenal hypoplasia
• 16. Diabetes insipidus
• 17. Sensitivity to smell of HCN
• 18. Brown teeth

11. 2. Y-linked inheritance
• In most species the Y chromosomes carry very few genes other than those
associated with sex determination. The following are some examples Y-
linked genes in humans:
• Webbed toes. This is characterized by a web-like connection between the
second and third toes. All sons have webbed toes while all daughters are
affected.
• Hypertrichosis of the ears. A conspicuous growth of hair on the outer rim
of the ear is transmitted only from father to son.

12. THANK YOU
BY: ARCEL T. INCLINO