What causes down syndrome? a deletion antibiotics a substitution nondisjunction

Nondisjunction.

Explanation:

Down Syndrome is a condition caused by trisomy 21, in which the person has 47 chromosomes instead of 46. The error in cell division called nondisjunction    (causes trisomy 21).

Nondisjunction Is the failure of paired chromosomes to divide during cell division, so in this division both chromosome go to one daughter cell. This cause errors in chromosomes number such as Down Syndrome (Trisomy 21) and turner syndrome (Monosomy X).

if the type of the food available changes, then the frequency of beak types will change, because birds with beaks more suited to the available food will be more successful over time.