Question 1

A human cell in G2 phase has just completed DNA replication. How many chromatids and chromosomes are present in this cell?

Accepted Answer

92 chromatids and 46 chromosomes

Question 2

During which specific stage of meiosis does crossing over occur, and what is its primary genetic consequence?

Accepted Answer

Prophase I; generates new allele combinations on homologous chromosomes

Question 3

A diploid organism with $$2n = 8$$ undergoes meiosis. Considering independent assortment only (no crossing over), how many genetically distinct gametes can it produce?

Accepted Answer

$$2^4 = 16$

Question 4

A couple, both carriers for an autosomal recessive disorder (genotype Aa), have two children. What is the probability that both children are carriers (Aa)?

Accepted Answer

$$\left(\frac{1}{2}\$$right)^2$$ = \frac{1}{4}$$

Question 5

Which of the following best describes the difference between homologous chromosomes and sister chromatids?

Accepted Answer

Homologous chromosomes have the same genes but may have different alleles; sister chromatids are identical copies formed during DNA replication

Question 6

A DNA sample is found to contain 18% guanine. What percentage of thymine does it contain?

Accepted Answer

32%

Question 7

Which enzyme is responsible for replacing RNA primers with DNA during DNA replication, and which enzyme seals the resulting nicks?

Accepted Answer

DNA polymerase replaces primers; DNA ligase seals nicks

Question 8

A cell with genotype AaBb (independent genes) undergoes meiosis. If the B/b chromosome pair flips orientation at metaphase I, what new gamete genotypes can result?

Accepted Answer

Ab and aB

Question 9

Which of the following statements about DNA replication is correct?

Accepted Answer

Replication is semi-conservative, producing two DNA molecules each with one old and one new strand

Question 10

A mRNA sequence is 5′-AUGCCUAAC-3′. What is the corresponding amino acid sequence (N- to C-terminus)? Use the standard genetic code.

Accepted Answer

Met-Pro-Asn

Question 11

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

Accepted Answer

Codon 5′-AUG-3′; Methionine

Question 12

In a pedigree, two unaffected parents have a child with a rare genetic disorder. What is the most likely mode of inheritance?

Accepted Answer

Autosomal recessive

Question 13

Which of the following best explains why all cells in your body (except gametes) have the same DNA but different functions?

Accepted Answer

Different cells express different genes due to different transcription factors at promoters

Question 14

During eukaryotic mRNA processing, which modification is important for mRNA stability and export from the nucleus?

Accepted Answer

Addition of a 5′ cap and a poly-A tail

Question 15

A cell is observed with chromosomes aligned single file at the metaphase plate, each consisting of two sister chromatids, and the cell is haploid. What stage is this?

Accepted Answer

Metaphase II of meiosis

Question 16

Which of the following is NOT a source of genetic variation in sexually reproducing organisms?

Accepted Answer

Replication of DNA during S phase

Question 17

A test cross is performed between a purple-flowered plant of unknown genotype and a white-flowered plant (recessive). All offspring are purple. What is the genotype of the purple parent?

Accepted Answer

Homozygous dominant

Question 18

Which of the following correctly describes the directionality of nucleic acid synthesis by DNA and RNA polymerases?

Accepted Answer

Both synthesize nucleic acids in the 5′ → 3′ direction

Question 19

A cell with $$2n = 6 is in $$anaphase of mitosis. How many chromosomes are present at this stage?

Accepted Answer

12

Question 20

Which of the following best explains the result of a nondisjunction event during meiosis I in humans?

Accepted Answer

Some gametes will have an extra chromosome (n+1) and some will have one less (n-1)

BIO 1610 Exam 2 Review: Cell Division, Genetics, and Molecular Biology

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