Practice questions · Topic 5.1

Unit 5 · Practice for the Topic 5.1 end-of-topic test

You’ve gone through everything in this topic. The summary video below recaps it all, so you’re ready for the questions.

Watch first: Meiosis, summed up

Video coming soon

One copying and two divisions; the pairs part in meiosis I and the count halves; the copies part in meiosis II; four haploid cells; the eight stages by what the cell shows; mitosis beside meiosis.

These are practice questions in the shape of the topic test. Work through them before you take the test; every question tells you what it wanted.

Answer every question. For each multiple-choice question, pick one option and press Check; the feedback gives the reasoning. For the free-response questions, write one short sentence for each step of your reasoning, each on its own line, and make every link clear (so, because, therefore). That is what the exam’s ‘paragraph form’ means for you: linked sentences, not bullet points. Show any calculation. The first free-response question walks you through one cell’s meiosis one part at a time, and you can open a hint for each part; the second is at the level of the test. When you finish a question, open the scoring guide and mark your own work against it. In every drawing, a chromosome from the mother is dark and one from the father is light.

Question 1

Six chromosomes from one of the animal’s cells, numbered 1 to 6.

An animal’s body cells hold six chromosomes. The six from one cell are drawn below and numbered 1 to 6; the mother’s chromosomes are dark and the father’s are light.

Which two chromosomes are a homologous pair?

A. Chromosomes 4 and 5 B. Chromosomes 1 and 2 C. Chromosomes 2 and 5 D. Chromosomes 1 and 4

Question 2

A red deer’s body cells each hold 68 chromosomes. A student says that any 34 of the 68 make one complete chromosome set.

Which of the following statements about the student’s claim is correct?

A. The student is right: a set is any half of the chromosomes B. The student is wrong: a set is all 68 chromosomes C. The student is right: any 34 chromosomes carry every gene once D. The student is wrong: a set is one chromosome of every pair, not any 34

Question 3

In a salamander, a sperm and an egg fuse.

Which term names the fusion of the two gametes?

A. Meiosis B. Mitosis C. Fertilization D. Cytokinesis

Question 4

A snail’s body cells hold 34 chromosomes. Its gametes hold 17 and its zygote holds 34, so its offspring’s body cells hold 34 as well.

Which statement explains why the count stays at 34 from one generation to the next?

A. A halving division before fertilization cancels the doubling at fertilization B. Fertilization keeps only one gamete’s set and discards the other C. Fertilization halves the two full sets the gametes bring to one set D. The zygote’s first mitosis halves the count back to 34

Question 5

One homologous pair from a locust cell in prophase I, with points J and K marked.

One homologous pair from a locust cell in prophase I is drawn below. Two points on the drawing are marked J and K.

Which of the following names the points J and K?

A. J a centromere, K a centromere B. J a centromere, K a chiasma C. J a chiasma, K a centromere D. J a chiasma, K a chiasma

Question 6

A moss’s cells that go through meiosis start with 40 chromosomes. To count chromosomes, count centromeres. A joined pair of sister chromatids is one chromosome, and a separated chromatid is one chromosome.

What is the chromosome count per cell after meiosis I?

A. 40 B. 20 C. 10 D. 80

Question 7

Two of the insect’s cells, numbered 1 and 2, with chromosomes across the middle.

An insect’s body cells hold eight chromosomes. Two of its cells are drawn below, numbered 1 and 2, each with its chromosomes across the middle of the cell. To count chromosomes, count centromeres. A joined pair of sister chromatids is one chromosome, and a separated chromatid is one chromosome.

Which drawing shows metaphase II?

A. Drawing 1 only B. Both drawings C. Neither drawing D. Drawing 2 only

Question 8

One of the two cells from a mouse’s meiosis I has begun to divide again.

Which statement describes this division?

A. The same four stages as mitosis, in a haploid cell B. A new pairing of homologs followed by their parting C. One more DNA copying followed by one division D. A division with no spindle, because the cell is haploid

Question 9

A cell in a turtle’s skin and a cell in its testis both divide.

What does each division produce?

A. Skin cell: two identical diploid cells; testis cell: four haploid cells B. Skin cell: four haploid cells; testis cell: two diploid cells C. Skin cell: two haploid cells; testis cell: four diploid cells D. Both: two identical diploid cells

Question 10

A female cod releases her eggs into the sea, and a male cod releases his sperm over them. Each egg that a sperm enters grows into a young cod.

Which of the following are the gametes?

A. The female’s and the male’s body cells B. The eggs and the sperm C. The eggs that sperm have entered D. The cells of the young cod

How to tackle the free-response questions. Read the verb first: describe asks what you see or know; explain asks why or how, so name the mechanism; predict asks what will happen and why; justify asks for the evidence that supports a claim. Each point is earned by one idea, stated in a sentence that names the thing and the mechanism. Extra words earn nothing; a wrong extra can lose the point. If there is a figure or table, use what it shows. When you finish, check the box for each point your answer earns and compare your sentences with the full-credit answer.

Free response 1 · Conceptual Analysis · 6 points

A radish’s body cells each hold 18 chromosomes. One cell in its anther, the part of the flower that makes pollen, copies its DNA and goes through meiosis. To count chromosomes, count centromeres. A joined pair of sister chromatids is one chromosome, and a separated chromatid is one chromosome.

(a) Calculate the number of homologous pairs in one of the radish’s body cells. (1 point)

Hint: How many chromosomes make up one homologous pair?

Write down the values in the question:

2 n = 18

Write down the equation:

pairs = n = \frac{2 n}{2}

Substitute the values into the equation:

pairs = \frac{18}{2} = 9

A full-credit answer: The cell holds 18 chromosomes, and a homologous pair is 2 chromosomes, so it has 9 pairs.

(b) Calculate the number of chromatids in the cell after it copies its DNA. (1 point)

Hint: What does copying do to each chromosome, and how many chromosomes are there?

Write down the values in the question:

2 n = 18

Write down the equation:

chromatids after copying = 2 \times 2 n

Substitute the values into the equation:

chromatids = 2 \times 18 = 36

A full-credit answer: After the copying, each chromosome is 2 chromatids, so the cell holds 36 chromatids.

(c) Calculate the number of chromosomes in each cell after meiosis I. (1 point)

Hint: Which partners part in meiosis I?

Write down the values in the question:

2 n = 18

Write down the equation:

chromosomes after meiosis I = n = \frac{2 n}{2}

Substitute the values into the equation:

chromosomes after meiosis I = \frac{18}{2} = 9

A full-credit answer: Each cell holds 9 chromosomes.

(d) Explain why each cell after meiosis I holds twice as many chromatids as chromosomes. (1 point)

Hint: Count the centromeres of one chromosome after meiosis I.

A full-credit answer: Each chromosome is still two sister chromatids joined at one centromere.
Chromosomes are counted by centromere.
So each cell has two chromatids for every chromosome: 18 chromatids and 9 chromosomes.

Check the box for each point your answer earns

the reason — each chromosome is two sister chromatids joined at one centromere, and chromosomes are counted by centromere.

Common slip: Saying meiosis I split the centromeres. Nothing splits at the centromere in meiosis I.

(e) Calculate the number of chromosomes in each cell after meiosis II. (1 point)

Hint: Which partners part in meiosis II, and were they already counted inside their chromosome?

Write down the values in the question:

n = 9

Write down the equation:

chromosomes after meiosis II = n

Substitute the values into the equation:

chromosomes after meiosis II = 9

A full-credit answer: Meiosis II parts the sister chromatids, so each cell still holds 9 chromosomes, each a single chromatid.

(f) Explain your answers to (c) and (e). (1 point)

Hint: Count centromeres: what does each cell receive in each division?

A full-credit answer: At meiosis I each cell receives one member of every homologous pair, so the count halves from 18 chromosomes to 9.
At meiosis II the two sister chromatids of each chromosome part, and each chromatid was already counted inside its chromosome, so each cell keeps 9.

Check the box for each point your answer earns

BOTH mechanisms — meiosis I gives each cell one member of every pair, so the count halves; AND meiosis II parts sister chromatids, each already counted as one chromosome, so the count stays.

Do not award: one mechanism alone.

Common slip: Saying the count halves twice. A second halving would give three and a half chromosomes.

Free-response score: 0 of 6

Free response 2 · Conceptual Analysis · 4 points

Two cells from an insect, whose body cells hold six chromosomes, are drawn below, numbered 1 and 2. Both are in meiosis, frozen while their chromosomes move toward the poles. To count chromosomes, count centromeres. A joined pair of sister chromatids is one chromosome, and a separated chromatid is one chromosome.

Two of the insect’s cells, numbered 1 and 2, frozen while their chromosomes move toward the poles.

(a) Identify the stage each cell is in. (1 point)

A full-credit answer: Cell 1 is in anaphase II; cell 2 is in anaphase I.

Check the box for each point your answer earns

cell 1 anaphase II and cell 2 anaphase I.

Do not award: anaphase of mitosis for cell 1; three chromatids reach each pole, half the insect’s six, so the cell is haploid and in meiosis II.

Common slip: Swapping the two. Whole X’s moving is meiosis I; single chromatids moving is meiosis II.

(b) Describe what the spindle pulls apart in each cell. (1 point)

A full-credit answer: In cell 2 the spindle pulls the two members of each homologous pair to opposite poles, each still two sister chromatids.
In cell 1 the spindle pulls the two sister chromatids of each chromosome to opposite poles.

Check the box for each point your answer earns

homologs in cell 2 (anaphase I), sister chromatids in cell 1 (anaphase II).

Common slip: Saying sister chromatids part in both. At anaphase I nothing splits at the centromere.

(c) Predict the chromosome count in each of the two cells that cell 2 produces. (1 point)

Write down the values in the question:

2 n = 6

Write down the equation:

chromosomes after meiosis I = n = \frac{2 n}{2}

Substitute the values into the equation:

chromosomes after meiosis I = \frac{6}{2} = 3

A full-credit answer: 3 chromosomes in each, one of every pair, each still two chromatids.

(d) Evaluate the claim that the four cells at the end of this insect’s meiosis are genetically identical to the cell that began it. (1 point)

A full-credit answer: The claim is not supported.
Each of the four cells holds one member of each homologous pair, not both.
The two members of a pair may carry different alleles.
So each cell carries only one allele of each pair, while the starting cell carried both.
Therefore the four cells differ genetically from the cell that began the meiosis.

Check the box for each point your answer earns

the judgement (the claim is not supported) AND the ground (each cell receives one member of each pair, and the members of a pair may carry different alleles).

Accept as the ground, any one of: each end cell holds one member of each pair, so half the chromosomes; the members of a pair may carry different alleles; crossing over gave new allele combinations.

Common slip: Saying the claim is wrong with no ground. Evaluate needs the judgement and the reason the biology gives for it.

Free-response score: 0 of 4

Multiple choice checked: 0 of 10 correct.

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