Q: If genes A and B are 10 cM apart, and genes B and C are 15 cM apart, what is the distance between genes A and C if the gene order is A–B–C?

$$10\ \text{cM} + 15\ \text{cM} = 25\ \text{cM}$$

Question 1

A geneticist observes that two genes, A and B, have a recombination frequency of 8%. What is the map distance between these genes, and are they considered linked?

Accepted Answer

8 cM; Yes, they are linked because they are less than 50 cM apart.

Question 2

Which of the following best describes the outcome of the Meselson-Stahl experiment after one round of DNA replication in light ($$ ^{14}N ) $$medium, starting with DNA labeled with heavy ($$ ^{15}N ) $$nitrogen?

Accepted Answer

All DNA molecules have intermediate density, supporting the semi-conservative model.

Question 3

A DNA template strand has the sequence 3'-TACGGTACC-5'. What is the corresponding mRNA sequence produced during transcription?

Accepted Answer

5'-AUGCCAUGG-3'

Question 4

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

Accepted Answer

Nonsense mutation; it introduces a premature stop codon, truncating the protein.

Question 5

If genes A and B are 10 cM apart, and genes B and C are 15 cM apart, what is the distance between genes A and C if the gene order is A–B–C?

Accepted Answer

$$10\ 	ext{cM} + 15\ 	ext{cM} = 25\ 	ext{cM}$$

Question 6

Which enzyme is responsible for joining Okazaki fragments during DNA replication?

Accepted Answer

Ligase

Question 7

A student is analyzing a dihybrid cross and observes a 1:1:1:1 phenotypic ratio in the offspring. What does this suggest about the genes involved?

Accepted Answer

The genes are unlinked and assort independently.

Question 8

During DNA replication, which direction does DNA polymerase synthesize the new strand?

Accepted Answer

5' to 3' direction

Question 9

A DNA sequence is mutated by the insertion of a single nucleotide. What is the most likely consequence of this mutation?

Accepted Answer

Frameshift mutation, which alters the reading frame of the gene.

Question 10

Which of the following statements about the genetic code is TRUE?

Accepted Answer

It is degenerate, meaning multiple codons can code for the same amino acid.

Question 11

A researcher finds that two genes are 52 cM apart on a chromosome. What can be concluded about their inheritance?

Accepted Answer

They assort independently, behaving as if unlinked.

Question 12

Which of the following best explains why the lagging strand is synthesized in fragments during DNA replication?

Accepted Answer

DNA polymerase can only add nucleotides in the 5' to 3' direction, so the lagging strand is synthesized discontinuously.

Question 13

If a gene has a recombination frequency of 1%, what is its map distance in centiMorgans (cM)?

Accepted Answer

$$1\ 	ext{cM}$$

Question 14

A segment of DNA is transcribed and translated as follows:
DNA template: 3'-TAC GAA CCT-5'
mRNA: 5'-AUG CUU GGA-3'
What is the resulting amino acid sequence?

Accepted Answer

Methionine–Leucine–Glycine

Question 15

Which of the following is a function of DNA polymerase during replication?

Accepted Answer

It adds nucleotides to the growing DNA strand and proofreads via 3'→5' exonuclease activity.

Question 16

A tRNA molecule has the anticodon 3'-UAC-5'. Which mRNA codon will it recognize, and which amino acid will it carry?

Accepted Answer

5'-AUG-3'; Methionine

Question 17

A patient has a genetic disorder caused by a single base substitution that changes a codon from GAG (glutamic acid) to GAA (also glutamic acid). What type of mutation is this?

Accepted Answer

Silent mutation

Question 18

Which of the following best describes the relationship between parental and recombinant gametes in a test cross involving linked genes?

Accepted Answer

Parental gametes are more frequent than recombinant gametes due to reduced crossing over.

Question 19

A student is given the following gene distances: A–B = 7 cM, B–C = 12 cM, and A–C = 19 cM. What is the correct gene order?

Accepted Answer

A–B–C

Question 20

Which of the following statements about the central dogma of molecular biology is correct?

Accepted Answer

DNA is transcribed into mRNA, which is then translated into protein.

Genetics Exam 2 Study Guide: Linkage, Gene Mapping, DNA Replication, and the Genetic Code

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