Sex-linked traits

Sex-linked traits

The human karyotype. http://fig.cox.miami.edu/

Inheritance of sex

• The male's sperm determines the sex of the offspring

• The sex chromosomes carry genes related to sexual development (e.g. sex organs, position of fat stores)

Sex-linked traits

• Sex chromosomes also carry genes not related to sex

• Examples are hemophilia and color blindness

• These characteristics are "sex-linked"

Color blindness

• person has difficulty seeing colors

Hemophilia

• person cannot easily form blood clots

• person has a high risk of losing blood, even from bruises

Cross between parents who are both carriers of hemophilia

Multiple Choice

What is the inheritance of color blindness an example of?

• co-dominance

• continuous variation

• karyotype cross

• sex linkage

Multiple Choice

For haemophilia, let H be the normal allele and h the mutant allele.

Which is the genotype of the unaffected male?

• X^hY

• X^HX^H

• X^HX^h

• X^HY

Multiple Select

Which of the following explains why color blindness is more common in males? Tick two.

• The mutant allele for color blindness is carried by the X chromosome.

• The mutant allele for color blindness is carried by the Y chromosome.

• Male has only one X chromosome, so either allele is expressed.

• Female has two X chromosomes, so either allele is expressed.

Fill in the Blanks

Color blindness is carried by the X chromosome.

A mother is a carrier of color blindness. Her husband has normal vision.

The probability of having a color blind offspring is

percent.

Multiple Choice

The diagram shows the sex chromosomes of a woman and of a man. Their genotypes for a recessive sex-linked condition are also shown.

What are the chances that their daughter will show the sex-linked condition?

• 0%

• 25%

• 50%

• 75%