SEX LINKED INHERITANCESex Determination: The human XY system

Nondisjunction: The failure of chromosomes to separate properly during one of the stages of meiosis (fig. 11-12)

This can produce gametes w/two sex chromosomes or no sex chromosomes. Results in abnormal # of sex chromo.

Nondisjunction disorders

Turner syndrome- female in appearance, w/o sex organs

45X or 45XO

Klinefelter syndrome- Male in appearance, sterile, 47XXY

Babies are not born without an X chromosome

What can we learn? X chromo. Is essential; gender is determined by presence/absence of Y

NONDISJUNCTION DISORDERS

SEX-LINKED INHERITANCE

SEX-LINKED GENETIC DISORDER Sex-linked: Genes carried on the X or Y Chromo. Which are

expressed more commonly in males. WHY? COLORBLINDNESS- Most caused by genes located on X chromo. Red-green is most common, 8% males; 1% females Carried on X chromo.; dominant allele is XC & recessive is Xc. Why more common in males? HEMOPHILIA- Bleeders disea se, protein AHF is missing. MUSCULAR DYSTROPHY- Progressive wasting away of muscle. Caused by defective version of the gene, dystrophin SEX-INFLUENCED TRAITS: Caused by a gene whose expression

differs in males & females, located on autosomes.

SEX-LINKED DISORDERS