301. Which statement correctly describes chromosome number and DNA content just before mitosis begins?
ⓐ. Chromosome number is unchanged, but DNA content has doubled
ⓑ. Chromosome number has doubled, but DNA content is unchanged
ⓒ. Both chromosome number and DNA content are halved
ⓓ. Both chromosome number and DNA content remain exactly as in early $G_1$
Correct Answer: Chromosome number is unchanged, but DNA content has doubled
Explanation: By the time a cell is about to enter mitosis, it has already passed through S phase, where DNA replication occurred. This means the amount of DNA in the cell is greater than it was in $G_1$. However, the chromosome number is still counted as unchanged because each chromosome consists of two sister chromatids joined together. The cell is therefore chromosomally the same in number, but richer in DNA content. This is a basic numerical principle of the cell cycle. Therefore, just before mitosis, chromosome number is unchanged while DNA content has doubled.
302. The reduction in chromosome number from diploid to haploid occurs during:
ⓐ. mitosis
ⓑ. meiosis I
ⓒ. meiosis II
ⓓ. S phase
Correct Answer: meiosis I
Explanation: Meiosis I is called the reductional division because it is the stage in which homologous chromosomes separate from each other. Since one chromosome from each homologous pair goes to each pole, the chromosome number is reduced to half. This changes the cells from diploid to haploid. Meiosis II does not reduce chromosome number further because it mainly separates sister chromatids. The reduction in chromosome number is therefore a specific feature of meiosis I. Hence, the diploid-to-haploid reduction occurs during meiosis I.
303. After completion of meiosis I, each daughter cell is best described as:
ⓐ. diploid with single-chromatid chromosomes
ⓑ. diploid with two-chromatid chromosomes
ⓒ. haploid with two-chromatid chromosomes
ⓓ. haploid with no chromosomes
Correct Answer: haploid with two-chromatid chromosomes
Explanation: At the end of meiosis I, homologous chromosomes have already separated, so the chromosome number in each daughter cell is haploid. However, the centromeres have not yet divided, so each chromosome still consists of two sister chromatids. This means the cells are reduced in chromosome number but not yet reduced in chromatid duplication. That is why meiosis II is still necessary afterward. The correct description must therefore include both haploid number and duplicated chromosomes. Hence, each daughter cell after meiosis I is haploid with two-chromatid chromosomes.
304. Which statement best describes the outcome of meiosis II with respect to chromosome structure?
ⓐ. Homologous chromosomes pair again and chromosome number is doubled
ⓑ. Sister chromatids separate, producing chromosomes with single chromatids
ⓒ. DNA replicates again before chromosome number is reduced further
ⓓ. Chromosome number becomes diploid again without fertilization
Correct Answer: Sister chromatids separate, producing chromosomes with single chromatids
Explanation: Meiosis II is an equational division that follows the reductional division of meiosis I. During this stage, the centromeres divide and sister chromatids separate from one another. As a result, the final chromosomes in the daughter cells are no longer duplicated. Each chromosome is represented by a single chromatid. This step completes the structural separation of chromosomal material in meiosis. Therefore, the correct outcome of meiosis II is separation of sister chromatids and production of single-chromatid chromosomes.
305. Which comparison between mitosis and meiosis is correct regarding chromosome number of daughter cells?
ⓐ. Mitosis halves chromosome number, whereas meiosis keeps it unchanged
ⓑ. Mitosis keeps chromosome number unchanged, whereas meiosis usually halves it
ⓒ. Both mitosis and meiosis always keep chromosome number unchanged
ⓓ. Both mitosis and meiosis always halve chromosome number
Correct Answer: Mitosis keeps chromosome number unchanged, whereas meiosis usually halves it
Explanation: Mitosis is designed to preserve the chromosome number of the parent cell in the daughter cells, which is why it is called equational. Meiosis, in contrast, includes a reductional division that lowers chromosome number from diploid to haploid. This difference reflects their biological roles. Mitosis is used for growth and repair, while meiosis prepares cells for sexual reproduction. The chromosome-number outcome is therefore one of the clearest distinctions between the two processes. Hence, mitosis keeps chromosome number unchanged, whereas meiosis usually halves it.
306. In a species with $2n = 8$, how many chromosomes will each daughter cell have after mitosis?
ⓐ. 2
ⓑ. 4
ⓒ. 8
ⓓ. 16
Correct Answer: 8
Explanation: If the diploid number of a species is 8, then a normal somatic cell contains 8 chromosomes. Mitosis maintains chromosome number, so the daughter cells formed after mitotic division will also each contain 8 chromosomes. Although DNA is duplicated before mitosis, the number of chromosomes does not permanently increase because the chromatids are distributed equally. This preserves the diploid state of the cells. Such constancy is essential for body tissues. Therefore, each daughter cell after mitosis will have 8 chromosomes.
307. In a species with $2n = 8$, how many chromosomes will each final cell have after completion of meiosis?
ⓐ. 2
ⓑ. 4
ⓒ. 8
ⓓ. 16
Correct Answer: 4
Explanation: If the diploid number is 8, then the haploid number is 4. Meiosis reduces chromosome number from diploid to haploid so that the final meiotic products contain only one chromosome from each homologous pair. After meiosis II, the resulting cells remain haploid and each chromosome is represented by a single chromatid. Thus, each final product contains 4 chromosomes. This reduction is the essential numerical outcome of meiosis. Therefore, each final cell after meiosis will have 4 chromosomes.
308. Which statement correctly distinguishes chromosome number from DNA content?
ⓐ. Chromosome number and DNA content always change together in the same way
ⓑ. DNA content may double without an immediate change in chromosome number
ⓒ. Chromosome number doubles in every S phase because DNA doubles
ⓓ. DNA content becomes irrelevant once chromosomes are visible
Correct Answer: DNA content may double without an immediate change in chromosome number
Explanation: Chromosome number and DNA content are related but not identical concepts. During S phase, the DNA content of the cell increases because replication occurs, but the chromosome number does not immediately change. Each replicated chromosome is still counted as one chromosome until sister chromatids separate. This is why DNA amount and chromosome number must be tracked separately in cell division. Confusing them leads to many common mistakes in biology. Therefore, the correct distinction is that DNA content can double without an immediate change in chromosome number.
309. The main numerical significance of meiosis in sexual reproduction is that it:
ⓐ. keeps all reproductive cells diploid
ⓑ. prevents DNA replication in germ cells
ⓒ. reduces chromosome number so fertilization can restore diploidy
ⓓ. doubles the chromosome number before gametes are formed
Correct Answer: reduces chromosome number so fertilization can restore diploidy
Explanation: In sexual reproduction, two reproductive cells fuse during fertilization. If these cells were not reduced in chromosome number beforehand, the chromosome number would increase generation after generation. Meiosis prevents this by producing haploid cells. When two haploid cells fuse, the diploid chromosome number is restored in the zygote. This maintains chromosomal constancy across generations. The numerical importance of meiosis is therefore directly tied to fertilization. Hence, meiosis reduces chromosome number so fertilization can restore diploidy.
310. Which statement best summarizes the changes in chromosome number and DNA content across mitosis and meiosis?
ⓐ. In both mitosis and meiosis, chromosome number and DNA content always change identically
ⓑ. Mitosis preserves chromosome number, while meiosis reduces it; DNA replication precedes division in both
ⓒ. Mitosis reduces chromosome number, while meiosis preserves it; DNA never changes before division
ⓓ. Meiosis II alone causes all numerical and structural changes in chromosomes
Correct Answer: Mitosis preserves chromosome number, while meiosis reduces it; DNA replication precedes division in both
Explanation: A full understanding of cell division requires tracking both chromosome number and DNA content. In mitosis, DNA replicates before division, but chromosome number is preserved in the daughter cells. In meiosis, DNA also replicates before the divisions begin, but chromosome number is reduced during meiosis I and finalized structurally in meiosis II. Thus, mitosis maintains ploidy, whereas meiosis changes it from diploid to haploid. This summary captures the core numerical differences between the two processes. Therefore, the best overall statement is that mitosis preserves chromosome number, while meiosis reduces it, and DNA replication precedes division in both.
311. Assertion (A): After S phase, a diploid cell may contain twice the earlier DNA amount without having twice the chromosome number.
Reason (R): Replication produces sister chromatids, but each replicated chromosome is still counted as one chromosome until chromatids separate.
ⓐ. Both A and R are true, and R is the correct explanation of A.
ⓑ. Both A and R are true, but R is not the correct explanation of A.
ⓒ. A is true, but R is false.
ⓓ. A is false, but R is true.
Correct Answer: Both A and R are true, and R is the correct explanation of A.
Explanation: The assertion is correct because DNA replication increases the total DNA content of the cell during S phase. However, chromosome number does not immediately double at that point. The reason is also correct because each chromosome, though now made of two sister chromatids, is still regarded as one chromosome as long as the centromere has not divided. This distinction between DNA amount and chromosome number is essential in cell-cycle analysis. The reason directly explains why DNA content can double without a corresponding change in chromosome count. Therefore, both statements are true, and the reason correctly explains the assertion.
312. In a species with $2n = 14$, how many bivalents will be seen at the equatorial plane during Metaphase I?
ⓐ. 14
ⓑ. 7
ⓒ. 28
ⓓ. 3
Correct Answer: 7
Explanation: In Metaphase I, homologous chromosomes align as paired units called bivalents. If the diploid number is 14, the haploid number is 7, which means there are 7 homologous pairs in the cell. Each homologous pair forms one bivalent. Therefore, the number of bivalents seen at the equator during Metaphase I equals the haploid number, not the diploid number. This is an important distinction between Metaphase I and mitotic metaphase. Hence, a species with $2n = 14$ will show 7 bivalents in Metaphase I.
313. In a species with $2n = 14$, each cell at Metaphase II will contain:
ⓐ. 14 chromosomes and 28 chromatids
ⓑ. 14 chromosomes and 14 chromatids
ⓒ. 7 chromosomes and 7 chromatids
ⓓ. 7 chromosomes and 14 chromatids
Correct Answer: 7 chromosomes and 14 chromatids
Explanation: After meiosis I, each daughter cell becomes haploid, so it contains 7 chromosomes in a species where $2n = 14$. However, those chromosomes are still duplicated because sister chromatids have not yet separated. Therefore, at Metaphase II, each chromosome still consists of two chromatids. This means each cell contains 7 chromosomes and 14 chromatids. The stage is therefore haploid in chromosome number but still doubled in chromatid structure. Hence, the correct description is 7 chromosomes and 14 chromatids.
314. In a species with $2n = 8$, what is the total number of chromosomes present in the whole cell during mitotic anaphase?
ⓐ. 4
ⓑ. 8
ⓒ. 16
ⓓ. 32
Correct Answer: 16
Explanation: Before mitotic anaphase, the cell has 8 chromosomes, each made of two sister chromatids. At anaphase, the centromeres divide and the sister chromatids separate. Once they separate, each chromatid is counted as an individual chromosome. Therefore, within the whole cell at that moment, the chromosome count temporarily becomes 16. This is a classic example of how chromosome number can change during separation even though the final daughter cells each receive the original diploid number. Hence, the total number of chromosomes in the cell during mitotic anaphase is 16.
315. In a species with $2n = 8$, which statement correctly describes Anaphase I of meiosis?
ⓐ. Each pole receives 4 chromosomes, and each chromosome still has two chromatids
ⓑ. Each pole receives 8 chromosomes, and each chromosome has one chromatid
ⓒ. The whole cell contains 16 chromosomes because centromeres divide
ⓓ. Each pole receives 2 chromosomes, and chromosome number becomes one-fourth
Correct Answer: Each pole receives 4 chromosomes, and each chromosome still has two chromatids
Explanation: In Anaphase I, homologous chromosomes separate from each other and move to opposite poles. Since the diploid number is 8, the haploid number is 4, so each pole receives 4 chromosomes. However, centromeres do not divide during this stage, so each migrating chromosome still consists of two sister chromatids. This is why meiosis I reduces chromosome number but does not yet separate chromatids. The stage is therefore reductional but not structurally final. Hence, each pole receives 4 chromosomes, each still with two chromatids.
316. A root tip cell shows 12 chromosomes aligned singly at the equator, with no evidence of bivalents or chiasmata. This cell is most likely in:
ⓐ. Metaphase I of meiosis
ⓑ. Diplotene of meiosis I
ⓒ. Metaphase II of meiosis
ⓓ. Metaphase of mitosis
Correct Answer: Metaphase of mitosis
Explanation: Root tip cells are somatic and typically undergo mitosis rather than meiosis. The description also shows chromosomes aligned singly, not as homologous pairs or bivalents. The absence of chiasmata further indicates that meiotic pairing and recombination are not involved. In Metaphase I of meiosis, homologous chromosomes align as bivalents, which is not the case here. Therefore, a root tip cell with singly aligned chromosomes at the equator is best identified as being in mitotic metaphase. Hence, the correct stage is Metaphase of mitosis.
317. Assertion (A): Interkinesis normally lacks DNA replication.
Reason (R): Meiosis II separates the same replicated sister chromatids that were retained after meiosis I.
ⓐ. Both A and R are true, but R is not the correct explanation of A.
ⓑ. Both A and R are true, and R is the correct explanation of A.
ⓒ. A is true, but R is false.
ⓓ. A is false, but R is true.
Correct Answer: Both A and R are true, and R is the correct explanation of A.
Explanation: The assertion is correct because interkinesis is only a brief interval between meiosis I and meiosis II and does not include a new S phase. The reason is also correct because the chromatids that separate in meiosis II are the same sister chromatids already formed before meiosis I. Since those chromatids are already present, a second round of DNA replication is unnecessary. This explains why meiosis can achieve two divisions after only one replication event. The reason directly clarifies the biological logic of interkinesis. Therefore, both statements are true and the reason correctly explains the assertion.
318. Which set contains only stages in which chromosome number remains the same as in $G_1$, but DNA content is greater than in $G_1$?
ⓐ. $G_1$ phase, metaphase of mitosis, telophase of mitosis
ⓑ. S phase, telophase I, cytokinesis
ⓒ. $G_2$ phase, prophase of mitosis, metaphase of mitosis
ⓓ. Anaphase of mitosis, telophase II, $G_0$ phase
Correct Answer: $G_2$ phase, prophase of mitosis, metaphase of mitosis
Explanation: After S phase, DNA has already replicated, so the cell contains more DNA than it did in $G_1$. However, the chromosome number remains the same until sister chromatids separate. In $G_2$, prophase, and metaphase of mitosis, the chromosomes are still counted as the same number as in $G_1$ because the chromatids remain joined. This makes those stages good examples of unchanged chromosome number with increased DNA content. The other options include stages where chromosome behavior differs or DNA has not yet been fully replicated. Hence, the correct set is $G_2$ phase, prophase of mitosis, and metaphase of mitosis.
319. In a species with $2n = 6$, one diploid cell completes mitosis and another identical diploid cell completes meiosis. What is the total number of chromosomes across all final daughter cells in each case, respectively?
ⓐ. 12 after mitosis and 12 after meiosis
ⓑ. 6 after mitosis and 12 after meiosis
ⓒ. 12 after mitosis and 6 after meiosis
ⓓ. 6 after mitosis and 6 after meiosis
Correct Answer: 12 after mitosis and 12 after meiosis
Explanation: In mitosis, one diploid cell with 6 chromosomes forms two daughter cells, each with 6 chromosomes, giving a total of 12 across both cells. In meiosis, the same diploid cell forms four haploid cells, each with 3 chromosomes, again giving a total of 12 across all final products. This shows that the total chromosomal material is distributed differently but not lost. The important difference is how that total is partitioned among daughter cells. Mitosis gives fewer cells with higher chromosome number, while meiosis gives more cells with lower chromosome number. Hence, the total is 12 after mitosis and 12 after meiosis.
320. If 8 bivalents are visible in a meiotic cell, how many chromatids are present in those bivalents altogether?
ⓐ. 16
ⓑ. 32
ⓒ. 8
ⓓ. 24
Correct Answer: 32
Explanation: One bivalent consists of two homologous chromosomes paired together. Since each chromosome has already replicated before meiosis I, each one contains two sister chromatids. Therefore, each bivalent contains a total of four chromatids. If there are 8 bivalents, the total number of chromatids is 8 × 4 = 32. This numerical relationship helps connect chromosome pairing with chromatid structure in meiosis I. Hence, 8 bivalents together contain 32 chromatids.
