Sex Linked Genes

The Xs and Ys of Genetics

Sex Linked Genes

• There are 23 pairs of chromosomes and one of those pairs are the sex chromosomes.

• There are either X chromosomes or Y chromosomes.

Sex Linked Genes

• These chromosomes not only carry the genes that determine male and female traits, but also those for some other characteristics as well.

• Genes that are carried by either sex chromosome (X or Y) are said to be SEX LINKED

Males

• Men normally have an X and a Y combination of sex chromosomes.

• Since only men inherit the Y chromosome, they are the only ones that inherit Y-linked traits.

Females

• Women have 2 X chromosomes

X Linked Traits

• Men and Women can get the X-linked traits since both inherit X chromosomes.

Sex inheritance patterns for male and female children

X Chromosome Traits

• Men only have one X chromosome

• Therefore genes on that chromosome are expressed in the male phenotype, even if it is a recessive gene.

X-linked traits

• In women, a recessive allele on one x chromosome is often masked on their phenotype

• May have a dominant normal allele on the other carriers of X-linked traits but more rarely have them expressed in their own phenotypes

X-linked traits

• In humans, at least 120 genes are known to be X-linked.

• Genes for hemophilia, red-green color blindness, congenital night blindness, and Duchene muscular dystrophy

Hemophilia

• An X-linked genetically inherited recessive disease

• Can not clot their blood

• Severe bleeding from minor cuts

• Mostly in males

Red-Green Color Blindness

• X-linked

• Cannot perceive red and green in the same

• Most often afflicts males

Muscular Dystrophy (MD)

• Characterized by a gradual irreversible wasting away of skeletal muscle.

• An X-linked trait most often passed on to sons from their mothers.

• Begins to weaken the legs of boys by age 3 and gets worse every year.

• No cure and inflicted usually die by age 30.

Y-linked Traits

• The Y chromosome is small and therefore does not contain many genes

• Y linked diseases are very rare

• Only passed from father to son.

• Example: Male infertility

Hypertrichosis Pinnae.

• Hairy ears • Can happen later in

life.• Y-linked