Question

an extra copy of chromosome 21 results in which genetic disorder?
a color - blindness
b down syndrome
c dwarfism
d cystic fibrous

Explanation:

Down syndrome is caused by an extra copy of chromosome 21. Color - blindness is a sex - linked disorder (usually related to X chromosome). Dwarfism can be due to various genetic or hormonal factors (not specifically an extra copy of chromosome 21). Cystic fibrosis is an autosomal recessive disorder caused by mutations in the CFTR gene (not related to an extra chromosome 21).

Answer:

B. Down syndrome