MCAT Genetics 2

Question 1

Trisomy 21 (Down syndrome) most commonly results from which of the following mechanisms?

Accepted Answer

Nondisjunction during meiosis

Answer

A deletion on chromosome 21

Answer

Robertsonian translocation involving chromosome 21

Answer

A point mutation in the DYRK1A gene

Question 2

DNA methylation of CpG islands in a gene's promoter region typically results in:

Accepted Answer

Gene silencing and decreased transcription

Answer

Increased gene expression due to enhanced polymerase binding

Answer

Increased mutation rate at that locus

Answer

Histone acetylation and chromatin relaxation

Question 3

During eukaryotic RNA processing, which modification is added to the 5' end of pre-mRNA?

Accepted Answer

A 7-methylguanosine (m7G) cap

Answer

A poly-A tail (200–250 adenine nucleotides)

Answer

A Kozak consensus sequence

Answer

An AAUAAA polyadenylation signal

Question 4

During translation, which RNA molecule carries specific amino acids to the ribosome?

Accepted Answer

tRNA (transfer RNA)

Answer

mRNA (messenger RNA)

Answer

rRNA (ribosomal RNA)

Answer

snRNA (small nuclear RNA)

Question 5

The lac repressor protein is inactivated (prevented from binding the operator) when it binds to:

Accepted Answer

Allolactose (a metabolite of lactose)

Answer

The operator DNA sequence directly

Answer

Cyclic AMP (cAMP)

Answer

RNA polymerase sigma factor

Question 6

Which of the following best defines genetic drift?

Accepted Answer

Random fluctuations in allele frequencies due to chance events, especially in small populations

Answer

Directed change in allele frequencies due to differential reproductive success

Answer

Movement of alleles between populations through migration

Answer

Changes in allele frequencies caused by new mutations

Question 7

In recombinant DNA technology, restriction endonucleases are primarily used to:

Accepted Answer

Cut DNA at specific palindromic recognition sequences

Answer

Synthesize new DNA strands from an RNA template

Answer

Join two DNA fragments with compatible ends

Answer

Amplify a specific DNA sequence exponentially