Lesson 7: Sex-Linked Traits

• Males and females have 23 pairs of chromosomes

  • Autosomes: 22 pairs

  • Sex Chromosomes: 1 pair

SEX-LINKED INHERITANCE

Sex-Linked

Traits controlled by genes on the sex chromosomes.

1. Color blindness

2. Duchenne Muscular Dystrophy

3. Fragile X-syndrome

4. Hemophilia

X-LINKED DISORDERS

Color blindness

• Inability to see green and red color.

• Most of the male affected by this disorder see brighter greens as tans, olive greens as browns, and reds as reddish browns.

• A few can’t tell reds from greens at all.

PEDIGREE FOR COLORBLINDNESS

Duchenne Muscular Dystrophy

• Disorder characterized by wasting away of the muscles.

• Muscle weakness intensifies until the individual is confined to a wheelchair.

• Death usually occurs by age 20; therefore affected males are rarely fathers.

• The cause is the absence of a protein Dystrophin.

Fragile X-syndrome

• Caused by abnormal number of repeat sequences I the genome and is the most common cause of inherited mental impairment.

• It is also associated with autism.

• Both male and female can be affected.

Hemophilia

• A rare bleeding disorder in which the blood doesn’t clot properly.

• Classified as mild, moderate, or severe, based on the amount of the clotting factor in the person’s blood.