Question 1

Which of the following best explains why meiosis is necessary for sexual reproduction in humans?

Accepted Answer

Meiosis reduces the chromosome number by half, preventing chromosome doubling in each generation after fertilization.

Question 2

During which specific phase of meiosis does crossing over occur, and what is its significance?

Accepted Answer

Crossing over occurs during prophase I and increases genetic variation among offspring.

Question 3

A human cell with 46 chromosomes undergoes meiosis. How many chromosomes will each resulting gamete contain, and what is the term for this chromosome number?

Accepted Answer

Each gamete will contain 23 chromosomes, which is called the haploid number ($$n).$$

Question 4

Which of the following events distinguishes meiosis I from mitosis?

Accepted Answer

Homologous chromosomes pair up and undergo crossing over during meiosis I, but not during mitosis.

Question 5

A child is born with three copies of chromosome 21. Which meiotic error most likely caused this condition, and what is the name of the disorder?

Accepted Answer

Nondisjunction during meiosis I; Down syndrome (trisomy 21)

Question 6

Which of the following best describes the difference between homozygous and heterozygous individuals at a specific gene locus?

Accepted Answer

Homozygous individuals have two identical alleles at a locus, while heterozygous individuals have two different alleles.

Question 7

If a diploid organism has a chromosome number of $$2n = 8$$, how many genetically unique gametes can it produce due to independent assortment alone (ignoring crossing over)?

Accepted Answer

$$2^4 = 16$

Question 8

Which of the following statements about genetic variation in sexually reproducing organisms is correct?

Accepted Answer

Genetic variation arises from crossing over, independent assortment, and random fertilization.

Question 9

During which stage of meiosis do homologous chromosomes align at the metaphase plate, and what is the significance of their arrangement?

Accepted Answer

Metaphase I; their random alignment leads to independent assortment of chromosomes.

Question 10

A woman with genotype $$Pp$$ for flower color (where $$P is $$dominant for purple and $$p is $$recessive for white) produces eggs. What proportion of her eggs will carry the $$p$$ allele?

Accepted Answer

$$\frac{1}{2}$$

Question 11

Which of the following best explains why siblings from the same parents can look very different from each other?

Accepted Answer

Siblings inherit different combinations of alleles due to independent assortment, crossing over, and random fertilization.

Question 12

Which of the following is a key difference between meiosis II and mitosis?

Accepted Answer

Meiosis II occurs in haploid cells, while mitosis occurs in diploid cells.

Question 13

A male child is born with an XYY karyotype. Which of the following most likely explains this chromosomal abnormality?

Accepted Answer

Nondisjunction of the Y chromosome during spermatogenesis in the father.

Question 14

Which of the following best describes the process and outcome of synapsis during prophase I of meiosis?

Accepted Answer

Homologous chromosomes pair up to form bivalents (tetrads), allowing crossing over to occur.

Question 15

If a cell fails to undergo crossing over during meiosis, what is the most likely consequence for the resulting gametes?

Accepted Answer

The gametes will have reduced genetic variation compared to normal gametes.

Question 16

Which of the following is true regarding the role of melanin in human populations living at different latitudes?

Accepted Answer

High melanin levels are advantageous in areas with high UV radiation because they help protect DNA from damage.

Question 17

Which of the following best summarizes the main purpose of mitosis compared to meiosis?

Accepted Answer

Mitosis produces genetically identical cells for growth and repair, while meiosis produces genetically diverse gametes for sexual reproduction.

Question 18

Which of the following is a direct result of independent assortment during meiosis?

Accepted Answer

Each gamete receives a random mix of maternal and paternal chromosomes.

Question 19

A cell with a diploid number of $$2n = 6$$ undergoes meiosis. After meiosis II, how many cells are produced and what is their chromosome number?

Accepted Answer

Four cells, each with three chromosomes ($$n = 3)$$

Meiosis and Sexual Reproduction: Molecular Biology of the Gene (Ch. 10)

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