Sex Linked Genes Sex Linked Genes Found on

Sex Linked Genes • Found on 23 rd chromosome. • If a gene is

How we sex linked genes • Look at XX or XY chromosomes – Place

Give it a try… Parent Father (Carrier) Gametes Children Mother (Heterozygous Normal)

Recessive vs. Dominant • X-linked recessive disorders: – Common red-green color-blindness. – Hemophilia. –

• • • Examples of Sex-linked Traits: Red-green colorblindness Male Pattern Baldness Hemophilia

Hemophilia • Hemophilia is an X-linked recessive disorder – Inability to properly form blood

Hemophilia continued… • Hemophilia affects – males much more frequently (1 in 10, 000).

Sample Sex-linked Trait Problem • In humans, red-green colorblindness is a recessive sex-linked trait.

Color Blindness Parent’s Phenotypes: • Normal Vision Father x Normal Vision Mother (Carrier) Phenotypes

Color Blindness Parent’s Phenotypes: • Normal Vision Father x Colorblind Mother Phenotypes of Offspring:

First, let’s take a look at Queen Victoria’s son Leopold’s family. His daughter, Alice

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Sex Linked Genes

Sex Linked Genes • Found on 23 rd chromosome. • If a gene is found only on the X chromosome and not the Y chromosome, it is said to be a sex-linked trait. • Sex linkage is linked to the gender of the individual.

X Chromosome

Y Chromosome

XR XR XR

How we sex linked genes • Look at XX or XY chromosomes – Place superscript letter above X chromosome. • Female Homozygous (Dominant) – XH XH • Female Heterozygous (Carrier) – XH Xh • Female Homozygous (Recessive) – Xh. Xh • Male Dominant – XH Y • Male Recessive – Xh. Y

Give it a try… Parent Father (Carrier) Gametes Children Mother (Heterozygous Normal)

Recessive vs. Dominant • X-linked recessive disorders: – Common red-green color-blindness. – Hemophilia. – Duchenne muscular dystrophy. • More males than females display the disease. • X-linked dominant are very rare in humans (ie. hypophosphatemia) and affected males pass the condition only to their daughters who may pass this on to both sons and daughters.

• • • Examples of Sex-linked Traits: Red-green colorblindness Male Pattern Baldness Hemophilia Duchenne Muscular Dystrophy Hairy Ears – Y Chromosome

Hemophilia • Hemophilia is an X-linked recessive disorder – Inability to properly form blood clots. • Until recently, hemophilia was untreatable, and only a few hemophiliacs survived to reproductive age because any small cut or internal hemorrhaging after even a minor bruise were fatal. • Hemophilia is treated with blood transfusions and Factor 7.

Hemophilia continued… • Hemophilia affects – males much more frequently (1 in 10, 000). – females (1 in 100, 000). • Since males only carry one X chromosome, if that is defective, hemophilia will immediately show up. • Females, carry two X chromosomes. – If only one is defective, the other normal X chromosome can compensate. The woman will have normal blood clotting; she will simply be a carrier of the recessive defective gene.

Sample Sex-linked Trait Problem • In humans, red-green colorblindness is a recessive sex-linked trait. • It is found on the X chromosome, not the Y. • Because, males only have one X chromosome, they have a much greater chance of having red-green colorblindness. – Females would have to be homozygous recessive in order to have red-green colorblindness.

Color Blindness Parent’s Phenotypes: • Normal Vision Father x Normal Vision Mother (Carrier) Phenotypes of Offspring: Females Normal Vision Males w/ Colorblindness

Color Blindness Parent’s Phenotypes: • Normal Vision Father x Colorblind Mother Phenotypes of Offspring: Females Normal Vision Males w/ Colorblindness

First, let’s take a look at Queen Victoria’s son Leopold’s family. His daughter, Alice of Athlone, had one hemophilic son (Rupert) and two other children—a boy and a girl—whose status is unknown. a) What is the probability that her other son was hemophilic? b) What is the probability that her daughter was a carrier? Hemophilic? c) What is the probability that both children were normal?