2. SEX LINKED INHERITANCE Sex 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

3. NONDISJUNCTION DISORDERS 

4. SEX-LINKED INHERITANCE 

5. 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 X C & recessive is X c.  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.

6. SEX-LINKED DISORDERS 