Gametes are formed by which process?

Question

Quizplus · Accepted Answer

Mitosis and binary fission are types of asexual reproduction. A gamete is a sex cell. Sex cells are produced by meiosis.
Meiosis is a process where a single parent cell divides twice to produce four daughter cells. These four daughter cells have only half of the chromosomes of the parent cell, making them haploid cells (haploid means a half set of chromosomes). Meiosis produces our sex cells, called gametes (sperm in males and eggs in females).
Meiosis happens in two distinct stages called meiosis I and meiosis II. Here are the steps of meiosis I and II, as well as the state of the cell before meiosis I and II begin (interphase).
BEFORE MEIOSIS I
Interphase: The chromosomes in the parent cell are duplicated, and the cell prepares for division. This parent cell now has a full set of chromosomes (46 chromosomes in human sex cells), making it a diploid cell (diploid means a full set of chromosomes).
MEIOSIS I
Prophase I: The chromosomes copied during interphase condense into X-shaped structures of two identical chromatids. These chromosomes then partner up to create homologous pairs (one chromosome from the father and one from the mother). The homologous pairs exchange bits of DNA in a process called crossing over, resulting in increased genetic variation. At the end of prophase I, the nuclear envelope (also called the nuclear membrane) breaks down.
Metaphase I: The homologous pairs of chromosomes line up in the middle of the cell along a line called the metaphase plate.
Anaphase I: The homologous pairs of chromosomes are pulled apart by the spindle and brought to opposite ends of the cell. Note that only the homologous pairs are split apart (they were only together to exchange some bits of DNA with each other), but the sister chromatids stay together, unlike mitosis and meiosis II.
Telophase I & Cytokenesis: The chromosomes gather together at opposite ends of the cell. A membrane forms around each set of chromosomes, forming two new nuclei. Then, the single cell pinches in the middle and splits to form two daughter cells in a process called cytokinesis. Each daughter cell has half as many chromosomes as the original parent cell (this would be 23 in human sex cells). This makes them haploid cells (haploid means half a set of chromosomes).
MEIOSIS II
Prophase II: In each of the two daughter cells, the chromosomes condense again into X-shaped structures. The membrane around the nucleus in each daughter cell disappears. Another meiotic spindle forms.
Metaphase II: In each of the two daughter cells, the chromosomes line up in the middle of the cell along a line called the metaphase plate. Fibers on the meiotic spindle attach to each of the sister chromatids.
Anaphase II: The sister chromatids are pulled apart by the meiotic spindle and brought to opposite ends of the cell. The separated chromatids are now individual chromosomes, just like mitosis.
Telophase II: The chromosomes gather together at opposite ends of the cell. A membrane forms around each set of chromosomes, forming two new nuclei. This is the end of meiosis.; however, cell division is not complete without undergoing one more round of cytokinesis. The two daughter cells pinch in the middle and split, yielding four daughter cells each with a half set of chromosomes (this makes them haploid cells). In males, these four cells are sperm cells. In females, one of these cells becomes an egg. A sperm cell will then fertilize an egg cell to produce a new organism.
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Gametes Are Formed by Which Process