MCAT Genetics 3

Question 1

During meiosis I, homologous chromosomes separate. This division reduces the chromosome number from:

Accepted Answer

Diploid (2n) to haploid (n)

Answer

Meiosis I is the reductional division where homologous chromosome pairs separate, halving the chromosome number from diploid (2n) to haploid (n) in each resulting cell.

Question 2

Phenylketonuria (PKU) is caused by a deficiency of which enzyme?

Accepted Answer

Phenylalanine hydroxylase

Answer

PKU results from a loss-of-function mutation in phenylalanine hydroxylase, which normally converts phenylalanine to tyrosine; deficiency leads to phenylalanine accumulation and neurotoxic metabolite production.

Question 3

An affected male with an X-linked recessive disorder has children with an unaffected, non-carrier female. What proportion of his daughters will be carriers?

Accepted Answer

100% — all daughters will be carriers

Answer

An affected male (X^a Y) passes his X^a chromosome to every daughter; since the mother provides only normal X alleles, all daughters will be obligate carriers (X^a X^N).

Question 4

During pre-mRNA splicing, which sequences are removed to produce mature mRNA?

Accepted Answer

Introns (intervening sequences)

Answer

Introns are non-coding intervening sequences excised from pre-mRNA by the spliceosome; the remaining exons are ligated together to form the mature mRNA that is translated.

Question 5

In PCR (polymerase chain reaction), which step separates the double-stranded DNA template into single strands?

Accepted Answer

Denaturation — high temperature breaks hydrogen bonds between base pairs

Answer

Denaturation (typically at ~94–98°C) disrupts the hydrogen bonds between complementary base pairs, unwinding the double helix into two single-stranded templates for subsequent primer annealing.

MCAT - Medical College Admission Test Practice Test

MCAT - Medical College Admission Test Practice Test

MCAT Genetics 3