Chromosome and Chromatid Counting Flashcards

Question 1

What does one DNA molecule mean when counting nuclear chromosomes?

Accepted Answer

One double-stranded DNA molecule

The two complementary strands together form one molecule in this counting convention. An unreplicated chromosome contains one such molecule.

Question 2

How do sister chromatids differ from the two chromosomes in a homologous pair?

Accepted Answer

Sisters are the two products of replicating one chromosome; homologs are the corresponding chromosomes in a diploid pair.

A replicated homologous pair therefore contains two chromosomes, each with its own sister pair.

Question 3

Before sister chromatids separate, how is one replicated chromosome counted?

Accepted Answer

One chromosome, two sister chromatids, two double-stranded DNA molecules

Once the sisters separate, each is a daughter chromosome. This is a counting convention for the joined unit, not a claim that replicated sisters share a single copy of centromeric DNA.

Question 4

Why must a chromosome-counting question say whether it means one cell, one nucleus, or one pole-bound group?

Accepted Answer

Those boundaries can contain different numbers of chromosomes.

Before cytokinesis is complete, two pole-bound groups or two re-formed nuclei can still lie inside one cell.

Question 5

What does n represent in a chromosome count?

Accepted Answer

The number of chromosomes in one complete haploid set

A diploid complement is 2n. Replication produces sister copies without adding another homologous set.

Question 6

For normal cell-division counting, what does “completed division, before the next S phase” specify?

Accepted Answer

Chromosome segregation and cytokinesis are finished, and the resulting cells have not replicated DNA again.

This avoids confusing a whole dividing cell with one final daughter cell.

Question 7

A normal diploid cell has 2n = 6. In its G1 nucleus, how many chromosomes and double-stranded DNA molecules are present?

Accepted Answer

6 chromosomes and 6 DNA molecules

Each chromosome is unreplicated and contains one double-stranded DNA molecule.

Question 8

In a normal diploid G1 nucleus, what are the ploidy and DNA amount? Let 1C mean the DNA amount in one unreplicated haploid set.

Accepted Answer

2n and 2C

The nucleus contains two homologous sets, each unreplicated. C measures DNA amount, not a number of molecules.

Question 9

A normal diploid nucleus starts G1 with 2n = 8. Across one completed S phase, how do its chromosome and double-stranded DNA-molecule counts change?

Accepted Answer

Chromosomes: 8 → 8. DNA molecules: 8 → 16.

Each chromosome acquires two joined sister chromatids. Replication doubles the DNA-molecule count without doubling the conventional chromosome count.

Question 10

A normal diploid cell has 2n = 6. After S phase is complete, in its G2 nucleus, how many chromosomes, attached sister chromatids, and DNA molecules are present?

Accepted Answer

6 chromosomes, 12 sister chromatids, and 12 double-stranded DNA molecules

The six replicated chromosomes each contain two sisters.

Question 11

In one whole cell at normal mitotic metaphase, with starting diploid complement 2n = 8, how many chromosomes, attached sister chromatids, and nuclear DNA molecules are present?

Accepted Answer

8 chromosomes, 16 sister chromatids, and 16 double-stranded DNA molecules

Replication is complete, and the sisters are still joined.

Question 12

A normal G1 nucleus has 2n = 10. A learner calls this “10 homologous pairs.” What is the correct pair count?

Accepted Answer

5 homologous pairs

The 10 counts individual chromosomes. Each homologous pair contains two chromosomes, so 10 ÷ 2 = 5.

Question 13

A cell with starting diploid complement 2n = 6 is in normal mitotic anaphase: all sisters have separated, but cytokinesis is incomplete. Count daughter chromosomes and nuclear DNA molecules in the whole cell.

Accepted Answer

12 daughter chromosomes and 12 double-stranded DNA molecules

The six replicated chromosomes have separated into twelve daughter chromosomes. Both pole-bound groups are still inside the counted cell.

Question 14

In a normal diploid G2 nucleus after completed replication, what are the ploidy and DNA amount? Let 1C mean the DNA amount in one unreplicated haploid set.

Accepted Answer

2n and 4C

There are still two homologous sets, but each chromosome is replicated. DNA amount has doubled from G1.

Question 15

In normal meiosis, is there another S phase between meiosis I and meiosis II?

Accepted Answer

No

One completed replication precedes the two divisions. Meiosis II separates the sisters that remain joined after meiosis I.

Question 16

A cell with diploid complement 2n = 8 completes normal mitosis and cytokinesis. Before another S phase, count chromosomes and nuclear DNA molecules in one daughter cell.

Accepted Answer

8 chromosomes and 8 double-stranded DNA molecules

Each daughter receives one copy of every chromosome in the starting diploid complement.

Question 17

Normal mitotic telophase has produced two re-formed nuclei, but cytokinesis is incomplete. Does “per nucleus” mean the same boundary as “per cell”?

Accepted Answer

No

One cell still contains both nuclei. A per-cell total includes the chromosomes in both nuclei; a per-nucleus count includes only one.

Question 18

A cell with starting diploid complement 2n = 6 is in normal mitotic anaphase after all sisters separate. Count daughter chromosomes and nuclear DNA molecules in the group moving toward one pole.

Accepted Answer

6 daughter chromosomes and 6 double-stranded DNA molecules

Each pole-bound group receives one daughter chromosome from each of the six replicated chromosomes.

Question 19

A normal diploid nucleus has 2n = 8. After completed S phase, a learner reports 16 chromosomes because DNA doubled. What chromosome count should replace 16?

Accepted Answer

8 chromosomes

There are 16 attached sister chromatids and 16 double-stranded DNA molecules, but each joined sister pair still counts as one chromosome.

Question 20

One whole cell with starting diploid complement 2n = 8 is at normal metaphase I. How many homologous pairs, chromosomes, attached sister chromatids, and nuclear DNA molecules are present?

Accepted Answer

4 homologous pairs, 8 chromosomes, 16 sister chromatids, and 16 double-stranded DNA molecules

Each pair contains two replicated homologs; each homolog contains two sisters.

Question 21

What separates in normal anaphase I, and how does that differ from normal mitotic anaphase?

Accepted Answer

Anaphase I separates homologous chromosomes; mitotic anaphase separates sister chromatids.

In meiosis I, each pole-bound chromosome still has its two sisters. In mitosis, separated sisters are daughter chromosomes.

Question 22

A cell with starting diploid complement 2n = 6 has completed normal mitotic chromosome segregation. Two nuclei have re-formed, but cytokinesis is incomplete. Count chromosomes and DNA molecules in one nucleus.

Accepted Answer

6 chromosomes and 6 double-stranded DNA molecules

That nucleus encloses one complete daughter complement. The other nucleus is outside the requested boundary.

Question 23

A cell with starting diploid complement 2n = 8 completes normal meiosis I and cytokinesis. Count chromosomes, attached sister chromatids, and nuclear DNA molecules in one resulting cell.

Accepted Answer

4 chromosomes, 8 sister chromatids, and 8 double-stranded DNA molecules

The cell has one homolog from each pair, with each chromosome still replicated.

Question 24

A normal mitotic cell began with 2n = 8 and has finished sister separation. What happens to the total number of nuclear DNA molecules when cytokinesis divides it into two cells, before any new replication?

Accepted Answer

The combined total stays 16; each daughter contains 8.

Cytokinesis changes the cell boundary. It partitions existing DNA rather than making or removing DNA molecules.

Question 25

One cell with starting diploid complement 2n = 8 is in normal anaphase I after homologs separate but before cytokinesis. Count chromosomes, attached sister chromatids, and nuclear DNA molecules in the whole cell.

Accepted Answer

8 chromosomes, 16 sister chromatids, and 16 double-stranded DNA molecules

Homologs move apart while each sister pair stays joined. Counting both pole-bound groups preserves the whole-cell total.

Question 26

After normal reciprocal crossing over is complete, does it change the chromosome or DNA-molecule count at metaphase I?

Accepted Answer

No

It changes DNA sequence combinations, not the completed-stage counts. Sisters need not remain genetically identical after crossing over.

Question 27

A cell with starting diploid complement 2n = 6 has completed normal mitotic segregation. Two nuclei have re-formed, but cytokinesis is incomplete. Count chromosomes and DNA molecules across both nuclei together.

Accepted Answer

12 chromosomes and 12 double-stranded DNA molecules

Each nucleus contains six. The requested total includes both nuclei inside the same cell.

Question 28

A parent with diploid complement 2n = 8 completed normal meiosis I. In one of its two cells at metaphase II, count chromosomes, attached sister chromatids, and nuclear DNA molecules.

Accepted Answer

4 chromosomes, 8 sister chromatids, and 8 double-stranded DNA molecules

Each cell retained one replicated homolog per pair. No second replication occurred.

Question 29

A cell with starting diploid complement 2n = 8 is in normal anaphase I after homologs separate. Count chromosomes, attached sister chromatids, and nuclear DNA molecules in the group moving toward one pole.

Accepted Answer

4 chromosomes, 8 sister chromatids, and 8 double-stranded DNA molecules

One replicated homolog from each of the four pairs moves toward that pole.

Question 30

In a normal mitotic cell, all sisters separate at anaphase before cytokinesis. Why can the chromosome count rise while the nuclear DNA-molecule count stays unchanged?

Accepted Answer

Existing sister copies become separate daughter chromosomes.

Sister separation changes what counts as a chromosome; it does not synthesize DNA. Replication occurred earlier in S phase.

Question 31

A normal diploid cell at mitotic metaphase contains 20 double-stranded nuclear DNA molecules in the whole cell. What is its diploid chromosome number, 2n?

Accepted Answer

2n = 10

Each of the replicated chromosomes has two DNA molecules, so 20 ÷ 2 = 10 chromosomes.

Question 32

A parent had diploid complement 2n = 8. In one normal meiosis-II cell, all sisters have separated at anaphase II but cytokinesis is incomplete. Count daughter chromosomes and nuclear DNA molecules in that whole cell.

Accepted Answer

8 daughter chromosomes and 8 double-stranded DNA molecules

Its four replicated chromosomes have separated into eight daughter chromosomes. This counts both poles of one meiosis-II cell.

Question 33

A parent with diploid complement 2n = 8 completes normal meiosis I, meiosis II, and both cytokineses. Before new replication, count chromosomes and nuclear DNA molecules in one final product.

Accepted Answer

4 chromosomes and 4 double-stranded DNA molecules

The product has one unreplicated haploid set.

Question 34

A parent with diploid complement 2n = 8 completed normal meiosis I. Both resulting cells are now at metaphase II. How do chromosome and nuclear DNA-molecule counts in one cell compare with the totals across both?

Accepted Answer

One cell: 4 chromosomes and 8 DNA molecules. Both cells: 8 chromosomes and 16 DNA molecules.

All DNA molecules are double-stranded. Each meiosis-II cell contains one replicated haploid set.

Question 35

During normal anaphase I, one pole-bound group contains 10 double-stranded nuclear DNA molecules, with sister pairs still joined. What was the starting diploid chromosome number, 2n?

Accepted Answer

2n = 10

Ten molecules make five replicated chromosomes at that pole. That group is one haploid set, so n = 5 and 2n = 10.

Question 36

A parent had diploid complement 2n = 8. In one normal meiosis-II cell at anaphase II, all sisters have separated. Count daughter chromosomes and nuclear DNA molecules in the group moving toward one pole.

Accepted Answer

4 daughter chromosomes and 4 double-stranded DNA molecules

One daughter chromosome from each of that cell’s four replicated chromosomes moves toward the chosen pole.

Question 37

A parent with 2n = 6 completes normal meiosis into four products. A learner counts 12 nuclear DNA molecules across all products and assigns 12 to each product. What belongs in one product before new replication?

Accepted Answer

3 double-stranded DNA molecules

Each product contains n = 3 unreplicated chromosomes. Twelve is the combined total across all four products.

Question 38

A normal meiotic parent had 2n = 6. After meiosis I and cytokinesis, one resulting cell contains 6 nuclear DNA molecules. A learner predicts 12 at metaphase II. Repair the prediction.

Accepted Answer

6 double-stranded DNA molecules at metaphase II

There is no S phase between the two meiotic divisions. The cell keeps three replicated chromosomes, each with two molecules.

Question 39

A cell with diploid complement 2n = 6 completes normal mitosis and cytokinesis. Before new replication, count chromosomes and nuclear DNA molecules across both daughter cells together.

Accepted Answer

12 chromosomes and 12 double-stranded DNA molecules

Each of the two daughters contains six. A combined total is larger than the count in either daughter.

Question 40

One whole cell at normal metaphase II contains 7 chromosomes. What was the diploid chromosome number, 2n, of the parent that began meiosis?

Accepted Answer

2n = 14

At metaphase II, the cell contains one replicated haploid set, so its seven chromosomes represent n = 7.

Question 41

After normal meiosis I and cytokinesis, what are the ploidy and DNA amount in one resulting cell? Let 1C mean the DNA amount in one unreplicated haploid set.

Accepted Answer

n and 2C

The cell has one homologous set, but every chromosome is still replicated.

Question 42

A normal G1 nucleus has 2n = 6. A learner counts 12 DNA molecules because DNA has two strands. What is the correct nuclear DNA-molecule count?

Accepted Answer

6 double-stranded DNA molecules

One unreplicated chromosome contains one double helix. Counting its two strands separately confuses strands with the molecule convention used here.

Question 43

A parent with diploid complement 2n = 8 completes normal meiosis into four products. Before new replication, count chromosomes and nuclear DNA molecules across all four products together.

Accepted Answer

16 chromosomes and 16 double-stranded DNA molecules

Each product has four unreplicated chromosomes. Four products × four chromosomes gives sixteen in total.

Question 44

A normal diploid G2 nucleus contains 12 attached sister chromatids after complete replication. How many chromosomes did its G1 nucleus contain?

Accepted Answer

6 chromosomes

Twelve sisters form six replicated chromosomes in G2. S phase kept the chromosome count at six.

Question 45

A normal meiosis-I product has one homolog from each pair, and every chromosome still has two sisters. A learner calls the cell diploid because of the sisters. Is that correct?

Accepted Answer

No: the cell is haploid.

Ploidy counts homologous sets. The sisters are replicated copies within its single set, so they do not make it diploid.

Question 46

An unspecified normal eukaryotic nucleus contains 8 double-stranded DNA molecules. Is that enough information to decide whether it is haploid or diploid?

Accepted Answer

No

You also need its replication state and the organism’s haploid complement. Eight molecules could, for example, be eight unreplicated chromosomes or four replicated chromosomes.

Question 47

After normal meiosis II and cytokinesis, before new replication, what are the ploidy and DNA amount in one final product? Let 1C mean the DNA amount in one unreplicated haploid set.

Accepted Answer

n and 1C

The product contains one haploid set of unreplicated chromosomes.

Question 48

One final product of normal meiosis contains 5 double-stranded nuclear DNA molecules before new replication. What were n and 2n for the diploid parent?

Accepted Answer

n = 5 and 2n = 10

Each final chromosome is unreplicated and contains one molecule, so this product has a five-chromosome haploid set.

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Chromosome and Chromatid Counting Flashcards