Question 1

A woman who is heterozygous for an X-linked recessive allele for red-green color blindness (X	extsuperscript{N}X	extsuperscript{n}) has children with a man who is not color blind (X	extsuperscript{N}Y). What is the probability that their son will be color blind?

Accepted Answer

0.25

Question 2

A patient is diagnosed with Klinefelter syndrome. Which of the following karyotypes and Barr body counts would you expect?

Accepted Answer

47, XXY; 1 Barr body

Question 3

Which of the following best explains why females heterozygous for an X-linked gene can be genetic mosaics?

Accepted Answer

Random X-inactivation in each cell during early embryonic development

Question 4

A cell with a diploid number of $$2n = 40$$ undergoes nondisjunction during meiosis II, resulting in a gamete with 21 chromosomes. If this gamete is fertilized by a normal gamete, what is the chromosome number of the resulting zygote?

Accepted Answer

$$2n + 1 = 41$$

Question 5

Which of the following statements about Down syndrome is correct?

Accepted Answer

It is usually caused by trisomy 21, most often due to nondisjunction in the ovum

Question 6

A scientist uses fluorescence in situ hybridization (FISH) to detect a specific DNA sequence. What is the principle behind this technique?

Accepted Answer

A fluorescently labeled nucleic acid probe hybridizes to its complementary DNA sequence on a chromosome

Question 7

Which enzyme is responsible for relieving supercoiling ahead of the replication fork during DNA replication?

Accepted Answer

Gyrase (topoisomerase)

Question 8

A mutation changes a codon from UAU (tyrosine) to UAA. What type of mutation is this, and what is the likely effect on the protein?

Accepted Answer

Nonsense mutation; translation will terminate prematurely

Question 9

Which of the following best describes the function of aminoacyl-tRNA synthetase?

Accepted Answer

It attaches the correct amino acid to its corresponding tRNA using ATP

Question 10

In the Meselson-Stahl experiment, E. coli were grown in $$^{15}N $$and then transferred to $$^{14}N. $$After one round of replication, what was observed and what did it demonstrate?

Accepted Answer

All DNA molecules had intermediate density, supporting semiconservative replication

Question 11

A patient is exposed to the toxin $$b-$$amanitin from Amanita phalloides. What is the molecular consequence of this exposure?

Accepted Answer

Inhibition of RNA polymerase II, blocking mRNA synthesis

Question 12

Which of the following is a property of the genetic code that allows multiple codons to specify the same amino acid?

Accepted Answer

Degeneracy

Question 13

A mutation in the Shine-Dalgarno sequence of a bacterial mRNA would most likely affect which process?

Accepted Answer

Initiation of translation by impairing ribosome binding

Question 14

Which of the following best distinguishes maternal inheritance from maternal effect?

Accepted Answer

Maternal inheritance involves organelle DNA, while maternal effect involves nuclear gene products deposited in the egg

Question 15

Which of the following antibiotics acts by mimicking aminoacyl-tRNA and causing premature chain termination during translation?

Accepted Answer

Puromycin

Question 16

A eukaryotic gene contains the sequence $$5'...GTAGGTAAGT...3' at $$the exon-intron boundary. What process will this sequence be directly involved in?

Accepted Answer

Splicing of pre-mRNA by the spliceosome

Question 17

Which of the following best explains why some antibiotics that target bacterial ribosomes can also cause side effects in human mitochondria?

Accepted Answer

Mitochondrial ribosomes are evolutionarily related to bacterial ribosomes and share similar features

Question 18

A cell contains both normal and mutant mitochondrial DNA. What is this condition called, and what is a likely consequence?

Accepted Answer

Heteroplasmy; variable severity of mitochondrial disease

Question 19

Which of the following best describes the role of the 23S rRNA in the bacterial ribosome?

Accepted Answer

It catalyzes peptide bond formation during translation

Question 20

A eukaryotic mRNA is translated efficiently only when a purine is present three bases upstream of the AUG start codon and a G is immediately after AUG. What is this sequence called, and what is its function?

Accepted Answer

Kozak sequence; it enhances start codon recognition during translation initiation

Genetics Exam 2 Study Guide: Sex Determination, Chromosomal Variation, DNA Structure, Replication, Transcription, and Translation

Study Guide - Practice Questions

Study Guide - Flashcards