In meiosis, how does prophase I differ from prophase II?
During prophase I there is one diploid cell; during prophase II there are two haploid cells.
During prophase I the nuclear envelope breaks up; during prophase II the nuclear envelope remains intact.
During prophase I chromosomes line up single file in the middle of the cell; during prophase II the chromosomes line up in double file in the middle of the cell.
During prophase I the chromosomes coil up; the chromosomes are not coiled up during prophase II.
In prophase I the sister chromatids are attached; in prophase II the sister chromatids are separated.
The correct answer and explanation is :
The correct answer is:
During prophase I there is one diploid cell; during prophase II there are two haploid cells.
Explanation:
Meiosis is a special type of cell division that reduces the chromosome number by half, producing four haploid cells from one original diploid cell. It has two major stages: Meiosis I and Meiosis II, and each of these stages includes prophase, metaphase, anaphase, and telophase.
Prophase I is unique and very important. During this phase, homologous chromosomes (one set from each parent) pair up in a process called synapsis. They physically connect to form structures called tetrads (groups of four chromatids). This stage is also when crossing over occurs—sections of genetic material are exchanged between homologous chromosomes, which increases genetic diversity. Importantly, at this point, the cell is diploid (2n), meaning it has two complete sets of chromosomes (one from each parent).
After Meiosis I ends, the cell has undergone a reductional division: homologous chromosomes have been separated into two new cells. Each new cell is now haploid (n)—it has only one set of chromosomes.
Then comes prophase II. This stage occurs in two haploid cells formed from Meiosis I. No pairing of homologous chromosomes or crossing over happens during prophase II because the homologous chromosomes have already been separated. Instead, in prophase II, chromosomes condense again, and a new spindle apparatus forms in each haploid cell in preparation for another division.
To address the incorrect choices:
- In both prophase I and prophase II, the nuclear envelope breaks down.
- Chromosomes do not line up during prophase; they line up during metaphase.
- Chromosomes are coiled in both prophase I and prophase II.
- Sister chromatids are still attached during prophase II; they only separate during anaphase II.
Thus, the key difference is that prophase I occurs in a diploid cell, while prophase II occurs in haploid cells.