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

Haploid (n) to diploid (2n)

Answer

Tetraploid (4n) to diploid (2n)

Answer

Haploid (n) to haploid (n)

Question 2

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

Accepted Answer

Phenylalanine hydroxylase

Answer

Tyrosine hydroxylase

Answer

Homogentisate dioxygenase

Answer

Fumarylacetoacetase

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

0% — daughters cannot inherit the X-linked allele from the father

Answer

25% — only one quarter of all children are carrier daughters

Answer

50% — half of all daughters will be carriers

Question 4

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

Accepted Answer

Introns (intervening sequences)

Answer

Exons (expressed sequences)

Answer

The 5' methylguanosine cap

Answer

The 3' poly-A tail

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

Annealing — primers bind to their complementary sequences

Answer

Extension — Taq polymerase synthesizes new strands

Answer

Ligation — DNA fragments are joined by ligase

Question 6

In CRISPR-Cas9 gene editing, the guide RNA (gRNA) functions to:

Accepted Answer

Direct the Cas9 endonuclease to a specific genomic sequence via complementary base pairing

Answer

Synthesize a new complementary DNA strand at the target site

Answer

Methylate the target DNA to silence the gene

Answer

Transcribe the target gene into mRNA

Question 7

Mendel's Law of Independent Assortment states that:

Accepted Answer

Alleles of different genes segregate independently during gamete formation

Answer

Alleles of the same gene always segregate into the same gamete

Answer

Genes located on the same chromosome always assort together

Answer

The dominant allele is always expressed over the recessive allele