21. (01.03 MC) How did cells survive on early Earth without oxygen? (5 points) O They used anaerobic respiration. They used aerobic respiration. They were scarce enough that they did not need oxygen. They used oxygen in the ocean water.

Duchenne muscular dystrophy is a serious condition caused by a recessive allele of a gene on the human x chromosome. the patients have muscles that weaken over time because they have absent or decreased dystrophin, a muscle protein. they rarely live past their twenties. how likely is it for a woman to have this condition? a) women can never have this condition.b) one-fourth of the daughters of an affected man would have this condition.c) one-half of the daughters of an affected father and a carrier mother could have this condition.d) only if a woman is xxx could she have this condition.