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 tells you what a wrong choice assumed. For the free-response questions, write your answer in full sentences and 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 teal and one from the father is dark.

Question 1

Six chromosomes from one toad cell, numbered 1 to 6.

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

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 cat’s body cells each hold 38 chromosomes.

How many chromosomes does a cat’s egg hold, and what is that set?

A. 38: one complete set B. 19: one complete set, one of every pair C. 19: half a set, missing some genes D. 76: two complete sets

Question 3

In a salamander, a sperm and an egg fuse.

Which name belongs to the fusing of the two gametes?

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

Question 4

A snail’s body cells hold 34 chromosomes, and so do the body cells of its offspring.

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 halves the count that two diploid gametes bring C. Mitosis after fertilization halves the count back to 34 in every body cell D. Each gamete carries 34 and the zygote keeps only one gamete’s set

Question 5

During a beetle’s meiosis, the two members of each homologous pair are pulled to opposite poles.

In which division does this happen, and what parts in the other division?

A. Meiosis II; meiosis I parts sister chromatids B. Meiosis I; meiosis II parts homologous pairs again C. Meiosis II; meiosis I copies the DNA D. Meiosis I; meiosis II parts sister chromatids

Question 6

A moss’s cells that go through meiosis start with 40 chromosomes.

What is the chromosome count per cell after meiosis I?

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

Question 7

Two katydid cells, numbered 1 and 2, with chromosomes across the middle.

Two cells from a katydid are drawn below, numbered 1 and 2, each with its chromosomes across the middle of the cell.

Which drawing shows metaphase II?

A. Drawing 1, because its chromosomes sit in pairs B. Drawing 1, because it holds more chromosomes than drawing 2 C. Drawing 2, because its chromosomes are all X-shaped D. Drawing 2, because its single chromosomes sit in one row

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, run on 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 frog’s skin and a cell in its testis both divide.

Which pair of outcomes is correct?

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

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 · 5 points

A plant’s body cells each hold 14 chromosomes. One cell in its anther copies its DNA and goes through meiosis.

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

Hint: How many chromosomes make up one homologous pair?

Write down the values in the question:

2 n = 14

Write down the equation:

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

Substitute the values into the equation:

pairs = \frac{14}{2} = 7

A full-credit answer: 7 homologous pairs.

(b) Calculate the number of chromatids in the cell after S phase. (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 = 14

Write down the equation:

chromatids after S phase = 2 \times 2 n

Substitute the values into the equation:

chromatids = 2 \times 14 = 28

A full-credit answer: 28 chromatids.

(c) Calculate the number of chromosomes in each cell after meiosis I, and describe the state of each chromosome. (1 point)

Hint: Which partners part in meiosis I, and what happens at the centromere?

A full-credit answer: 7 chromosomes, one of every pair, each still two sister chromatids joined at its centromere.

Check the box for each point your answer earns

7 chromosomes, each still two sister chromatids.

Common slip: Writing 14. Meiosis I parts the pairs and halves the count.

(d) 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 = 7

Write down the equation:

chromosomes after meiosis II = n

Substitute the values into the equation:

chromosomes after meiosis II = 7

A full-credit answer: 7 chromosomes, each a single chromatid.

(e) Explain why the chromosome count halves at meiosis I and stays the same at meiosis II. (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 14 to 7. At meiosis II the two sister chromatids of each chromosome part, and each chromatid was already counted inside its chromosome, so each cell keeps 7.

Check the box for each point your answer earns

meiosis I gives one of each pair (halving); meiosis II parts sister chromatids, already counted as one chromosome (no change).

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

Free-response score: 0 of 5

Free response 2 · Conceptual Analysis · 4 points

Two cells from a cricket, 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.

Cell 1: three V-shaped single chromatids moving toward each pole in a small cell. Cell 2: three whole X-shaped chromosomes moving toward each pole.

(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 cricket’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 is being pulled 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) Explain why the four cells at the end of this cricket’s meiosis differ genetically from the cell that began it. (1 point)

A full-credit answer: Each of the four cells holds only one member of each homologous pair, and the two members of a pair may carry different alleles, so no cell carries the same alleles as the diploid cell that began meiosis, and the four differ from one another.

Check the box for each point your answer earns

each cell gets one member of each pair, and the members of a pair may carry different alleles.

Common slip: Saying the cells differ only because they are haploid. The count alone does not make them different; the alleles on the two members of a pair do.

Free-response score: 0 of 4

Multiple choice checked: 0 of 9 correct.

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