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

1:1:1:1

Answer

3:1

Answer

1:2:1

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

Natural selection is actively occurring

Answer

Mating is nonrandom within the population

Answer

Population size is very small

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 helicase

Answer

DNA primase

Answer

DNA ligase

Question 4

A missense mutation results in which of the following outcomes?

Accepted Answer

A different amino acid incorporated into the protein

Answer

A premature stop codon

Answer

No change in the amino acid sequence

Answer

Deletion of an entire codon

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

The repressor binds the operator and blocks transcription

Answer

The catabolite activator protein (CAP) remains inactive

Answer

The lac structural genes are not transcribed

Question 6

Two genes are said to be genetically linked when they are:

Accepted Answer

Located on the same chromosome

Answer

Located on different homologous chromosomes

Answer

Always segregating independently during meiosis

Answer

Showing a 9:3:3:1 ratio in dihybrid crosses

Question 7

Which of the following correctly describes the central dogma of molecular biology?

Accepted Answer

DNA → RNA → Protein

Answer

Protein → RNA → DNA

Answer

DNA → Protein → RNA

Answer

RNA → DNA → Protein