MCAT Genetics

Question 1

In a dihybrid cross between two heterozygous parents (AaBb × AaBb), what is the expected phenotypic ratio in the offspring?

Accepted Answer

9:3:3:1

Answer

A dihybrid cross between two double heterozygotes yields a 9:3:3:1 phenotypic ratio when the genes assort independently, producing four distinct phenotypic classes.

Question 2

According to Hardy-Weinberg equilibrium, which condition must be met for a population to remain in equilibrium?

Accepted Answer

Allele and genotype frequencies remain constant across generations

Answer

Hardy-Weinberg equilibrium describes a state where allele and genotype frequencies remain constant generation after generation in the absence of evolutionary forces.

Question 3

During DNA replication, which enzyme synthesizes new DNA strands in the 5' to 3' direction by adding nucleotides to the growing chain?

Accepted Answer

DNA polymerase III

Answer

DNA polymerase III is the primary replicative polymerase in prokaryotes, extending the new strand by adding deoxyribonucleotides to the 3'-OH end in the 5' to 3' direction.

Question 4

A missense mutation results in which of the following outcomes?

Accepted Answer

A different amino acid incorporated into the protein

Answer

A missense mutation changes a single nucleotide, altering the codon so that a different amino acid is incorporated at that position in the polypeptide chain.

Question 5

In E. coli, when glucose is absent and lactose is present, which statement best describes the state of the lac operon?

Accepted Answer

The operon is transcribed at high levels due to both positive and negative regulation

Answer

With glucose absent, cAMP levels rise and activate CAP to stimulate transcription; with lactose present, allolactose inactivates the repressor, resulting in high-level transcription of the lac operon.

MCAT - Medical College Admission Test Practice Test

MCAT - Medical College Admission Test Practice Test

MCAT Genetics