Question

question 3
recessive alleles seem to vanish in some generations because:
a they cannot be expressed in males
b they cannot be expressed in females
c they cannot be expressed in successive generations
d they are masked by a dominant allele
question 4
why is amniocentesis usually performed?
a to detect fetal abnormalities in chromosome number
b to detect problems with the placenta
c to determine the sex of the fetus
d to determine if gene therapy is indicated
e to assess the risk of premature birth
question 5

Explanation:

For Question 3, recessive alleles are masked by dominant alleles in heterozygous individuals, which makes them seem to disappear in some generations. For Question 4, amniocentesis is a prenatal - diagnostic test mainly used to detect fetal chromosomal abnormalities.

Answer:

Question 3: D. They are masked by a dominant allele
Question 4: A. to detect fetal abnormalities in chromosome number