End-of-topic test: Meiosis and Genetic Diversity

Unit 5 · Topic 5.2 end-of-topic test

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 two free-response questions, write your answer in full sentences and show any calculation, then 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

A plant’s body cells hold six chromosomes: a long pair, a medium pair and a short pair, one member of each pair from each parent.

Which set could one of the plant’s gametes carry?

A. Both members of the long pair and the paternal short B. The paternal long, the paternal medium and the maternal short C. All three maternal chromosomes and all three paternal D. The maternal long and the paternal long only

Question 2

A midge cell at metaphase I: in the long pair the maternal (teal) member faces the left pole; in the short pair the paternal (dark) member faces the left pole.

A cell from a midge with one long pair and one short pair is drawn below at metaphase I. Meiosis then finishes normally.

Which two kinds of gamete does this one cell produce?

A. Maternal long with maternal short, and paternal long with paternal short B. All four kinds, every combination of one long and one short C. Maternal long with paternal short, and paternal long with maternal short D. Maternal long with paternal long, and maternal short with paternal short

Question 3

A moth has 5 pairs of chromosomes.

How many kinds of gamete can one moth make by independent orientation alone?

A. 10 B. 25 C. 16 D. 32

Question 4

A paired pair: a teal X with chromatids 1 and 2 and a dark X with chromatids 3 and 4.

A paired homologous pair from a wasp is drawn below in prophase I, with its four chromatids numbered 1 to 4.

Which two chromatids could exchange pieces by crossing over?

A. Chromatids 1 and 4 B. Chromatids 1 and 2 C. Chromatids 3 and 4 D. Any two of the four

Question 5

After meiosis in a yeast cell, one of the four cells carries an allele whose DNA sequence differs by one base from the allele on either homolog of the parent cell.

Which event made the new allele?

A. Crossing over between non-sister chromatids B. A mutation, a change in the DNA itself C. Independent orientation of the pair D. Anaphase II parting the sister chromatids

Question 6

The hamster’s pair after one crossover: the four chromatids read G H, G h, g h and g H.

In a hamster, one homolog of a pair carries G at one position and H at the next; the other homolog carries g and h. One crossover happens between the two positions. The four chromatids afterward are drawn below.

Which chromatid is recombinant?

A. A chromatid reading G and H B. A chromatid reading g and h C. Every chromatid, because all four broke D. A chromatid reading G and h

Question 7

In a species of frog, each parent makes 8 kinds of gamete by independent orientation.

How many kinds of zygote can two frogs make, counting independent orientation and random fertilization only?

A. 8 B. 16 C. 64 D. 4,096

Question 8

A starfish sheds eggs and sperm into the sea, where they meet.

Which statement places random fertilization correctly?

A. It is the last stage of meiosis II B. It happens between meiosis I and meiosis II C. It happens inside the ovary before meiosis begins D. It happens after meiosis has finished, between two gametes

Question 9

A trout egg carries the maternal copy of chromosome 2 and the paternal copy of chromosome 5.

Which source of variation put that combination together?

A. Independent orientation B. Crossing over C. Random fertilization D. Mutation

Question 10

Two lambs born to the same ewe and the same ram carry different combinations of their parents’ alleles.

Which statement explains the difference?

A. Mitosis in each lamb changed its alleles as the lamb grew after fertilization B. Each lamb grew from a different egg meeting a different sperm C. The ewe’s chromosomes all went into one lamb and the ram’s into the other D. The two lambs received different numbers of chromosomes from their parents

Question 11

A student notices that pollen from plants grown in a hot greenhouse contains more recombinant gametes than pollen from plants grown outdoors.

Which question about this observation is testable as written?

A. Why does heat matter so much to meiosis in these greenhouse plants? B. Is recombination good for the plant when the greenhouse is hot? C. Does a higher temperature raise the fraction of recombinant gametes? D. What is the purpose of crossing over in plants grown in hot weather?

Question 12

In a lily cell in meiosis, the spindle pulls, and the two identical copies that make up one chromosome move together to one pole instead of parting. Every other chromosome parts normally.

Which statement names what has happened?

A. Nondisjunction in meiosis II: two sister chromatids failed to part B. Nondisjunction in meiosis I: two homologs failed to part C. Crossing over between two sister chromatids D. Independent orientation: the chromosome faced one pole

Question 13

A locust cell at anaphase I, two of its twelve pairs drawn: both members of the long pair move toward the left pole; the short pair parts normally.

A locust’s body cells hold 24 chromosomes. In one cell, drawn below at anaphase I, both members of one homologous pair move to the same pole; meiosis II then runs normally. Only two of the cell’s twelve pairs are drawn.

What are the chromosome counts of the four cells produced?

A. 13, 11, 12 and 12 B. 13, 13, 11 and 11 C. 13, 12, 12 and 12 D. 24, 24, 12 and 12

Question 14

A human egg with 22 chromosomes is fertilized by a sperm with the normal 23.

What does the zygote hold?

A. 46 chromosomes, because the sperm makes up the missing one B. 44 chromosomes: two copies of one of them missing C. 45 chromosomes: one copy of one of them, a monosomy D. 47 chromosomes: three copies of one of them, a trisomy

Question 15

A child has three copies of chromosome 13 in every body cell.

Which gamete could have produced this zygote?

A. A sperm carrying all 46 of the father’s chromosomes B. An egg or sperm with 24 chromosomes, two copies of chromosome 13 C. A zygote that copied chromosome 13 twice after fertilization D. A gamete with 22 chromosomes, missing chromosome 13

Question 16

In a cell at metaphase I, the long pair has its maternal member facing the left pole.

What does that tell you about which way the short pair faces?

A. The short pair’s maternal member must face left too B. The short pair’s maternal member must face right, to balance C. Nothing: the short pair faces either way regardless of the long pair D. The short pair faces whichever way its longer neighbor faced in the last division

Question 17

In a lizard, one homolog carries alleles M and N at two positions and the other carries m and n. After meiosis with one crossover between the two positions, a gamete carries a chromosome reading m and n.

Which name fits the combination m with n?

A. Recombinant: a combination neither homolog had B. Parental: the combination one homolog already carried C. A new allele made by the crossover D. A sister chromatid of the M N chromosome

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 · Scientific Investigation · 4 points

A mouse’s body cells hold 40 chromosomes. The four cells produced by one meiosis in a male mouse were counted, and their chromosome counts are drawn below.

The four cells from one meiosis in a mouse, with their chromosome counts: 21, 19, 20 and 20.

(a) Identify the division in which a pair failed to separate, and justify your answer from the counts. (1 point)

A full-credit answer: The failure was in meiosis II. Two of the four cells hold the normal count of 20, so meiosis I parted every pair correctly; only one of the two cells from meiosis I gave an abnormal pair of cells, 21 and 19.

Check the box for each point your answer earns

meiosis II, because two cells are normal (20), which a failure in meiosis I could not leave.

Common slip: Choosing meiosis I because there is a 21 and a 19. Both patterns have a cell over and a cell under; the two normal cells place the failure.

(b) Describe what happened at anaphase in the division that failed. (1 point)

A full-credit answer: At anaphase II, in one of the two cells, the two sister chromatids of one chromosome did not separate; both went to the same pole, so one cell received an extra chromosome and the other received none of that chromosome.

Check the box for each point your answer earns

at anaphase II the two sister chromatids of one chromosome went to the same pole (nondisjunction).

Common slip: Saying two homologs failed to part. Homologs part in meiosis I; in meiosis II the partners are sister chromatids.

(c) Predict the four counts if the failure had happened in meiosis I instead, with meiosis II normal. (1 point)

A full-credit answer: 21, 21, 19 and 19: both members of one pair go to one cell in meiosis I, so one cell has 21 and the other 19, and meiosis II gives two cells of each.

Check the box for each point your answer earns

21, 21, 19, 19.

Common slip: Giving 21, 19, 20, 20. That is the meiosis II pattern; a meiosis I failure leaves no normal cell.

(d) Predict the chromosome number of the zygote made when the 21-chromosome sperm fertilizes a normal egg, and identify the zygote as a trisomy or a monosomy. (1 point)

A full-credit answer: 41 chromosomes: 21 from the sperm and 20 from the egg, so two copies of every chromosome and three copies of one, a trisomy.

Check the box for each point your answer earns

41, a trisomy (three copies of one chromosome).

Common slip: Calling it a monosomy. A gamete with one chromosome too many gives three copies of that chromosome, a trisomy.

Free-response score: 0 of 4

Free response 2 · Conceptual Analysis · 4 points

In zebrafish, the genes A and B sit on two different chromosome pairs. Two AaBb parents were crossed. One AaBb offspring formed from an AB egg and an ab sperm; another AaBb offspring formed from an Ab egg and an aB sperm.

(a) Explain how one mother can make both AB eggs and Ab eggs. (1 point)

A full-credit answer: The A gene and the B gene sit on different chromosome pairs, and each homologous pair lines up at metaphase I facing either way regardless of the other pairs, so which member of each pair an egg receives is decided pair by pair: the chromosome carrying A can go with the one carrying B or with the one carrying b.

Check the box for each point your answer earns

independent orientation, each pair facing either way at metaphase I on its own, so A goes with B or with b.

Common slip: Naming crossing over. The two genes are on different pairs, so no exchange between chromatids is needed for A to go with b.

(b) Suppose instead that A and B sat on the same chromosome, with A and B on one homolog and a and b on the other. Describe how a gamete could still receive A with b. (1 point)

A full-credit answer: In prophase I, while the homologs are paired, a chromatid of one homolog and a chromatid of the other break at the same point, between the two positions, and exchange the pieces, so a chromatid carries A with b, a combination neither homolog had.

Check the box for each point your answer earns

crossing over between non-sister chromatids in prophase I, breaking at the same point between the genes and exchanging pieces.

Common slip: Saying sister chromatids swap. Sister chromatids are identical copies; a swap between them changes nothing.

(c) Explain how random fertilization adds variation beyond what meiosis made in each parent. (1 point)

A full-credit answer: Meiosis made every egg and every sperm a different combination, and any egg can meet any sperm, so each zygote joins one of the mother’s kinds with one of the father’s; the kinds of zygote are the kinds of egg multiplied by the kinds of sperm.

Check the box for each point your answer earns

any egg can meet any sperm, so the combinations multiply beyond the gametes’ own variety.

Common slip: Saying fertilization makes the gametes vary. The gametes varied already; fertilization multiplies the combinations by pairing them at random.

(d) Calculate the number of different combinations of one egg with one sperm these two parents can make, if each parent makes four kinds of gamete: AB, Ab, aB and ab. (1 point)

Write down the values in the question:

kinds of egg = 4

kinds of sperm = 4

Write down the equation:

combinations = kinds of egg \times kinds of sperm

Substitute the values into the equation:

combinations = 4 \times 4 = 16

A full-credit answer: 16 combinations of one egg with one sperm.

Do not award for 9: that counts distinct genotypes among the young, not combinations of one egg with one sperm; the task asks for combinations.

Free-response score: 0 of 4

Multiple choice checked: 0 of 17 correct.

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