The four stages of meiosis I are as follows, according to " Molecular Biology of the Cell. Prophase I : At this stage, chromosomes become compact, dense structures and are easily visible under the microscope.
The homologous chromosomes pair together. The two sets of sister chromatids resemble two X's lined up next to each other. Each set exchanges bits of DNA with the other and recombines, thus creating genetic variation. This process is known as crossing over, or recombination. Even though in humans the male sex chromosomes X and Y are not exact homologs, they can still pair together and exchange DNA.
Crossing over occurs within only a small region of the two chromosomes. Metaphase I : The meiotic spindle, a network of protein filaments, emerges from two structures called the centrioles, positioned at either end of the cell. The meiotic spindle latches onto the fused sister chromatids. By the end of metaphase I, all the fused sister chromatids are tethered at their centromeres and line up in the middle of the cell.
The homologs still look like two X's sitting close together. Anaphase I : The spindle fibers start to contract, pulling the fused sister chromatids with them.
Each X-shaped complex moves away from the other, toward opposite ends of the cell. Telophase I : The fused sister chromatids reach either end of the cell, and the cell body splits into two. Meiosis I results in two daughter cells, each of which contains a set of fused sister chromatids. The genetic makeup of each daughter cell is distinct because of the DNA exchange between homologs during the crossing-over process.
In other words, by the end of the process, the chromosome number is unchanged between the cells that enter meiosis II and the resulting daughter cells. Prophase II : The nuclear membrane disintegrates, and meiotic spindles begin to form once again. Metaphase II : The meiotic spindles latch onto the centromere of the sister chromatids, and they all line up at the center of the cell.
Anaphase II : The spindle fibers start to contract and pull the sister chromatids apart. Each individual chromosome now begins to moves to either end of the cell. Telophase II : The chromosomes reach opposite ends of the cell. The nuclear membrane forms again, and the cell body splits into two.
Meiosis II results in four haploid daughter cells, each with the same number of chromosomes. However, each chromosome is unique and contains a mix of genetic information from the maternal and paternal chromosomes in the original parent cell.
If chromosomes fail to segregate completely, it's called nondisjunction and can result in the formation of gametes that have missing or extra chromosomes, according to "Molecular Biology of the Cell, 4th edition. How many chromosomes are in the daughter cells produced from mitosis? Michael B. Jan 11, It's the same as its mother cell. Explanation: If a human cell undergoes mitosis its daughter cells will have There is no change in chromosome number in mitosis.
Denise Granger. Jan 15, A human cell have 46 total or 23 pairs of chromosomes. Open survey. In: Facts In the Cell. During meiosis one cell divides twice to form four daughter cells. These four daughter cells only have half the number of chromosomes of the parent cell — they are haploid.
Meiosis produces our sex cells or gametes eggs in females and sperm in males. These are divided between the first time the cell divides meiosis I and the second time it divides meiosis II : Meiosis I 1. Interphase: The DNA in the cell is copied resulting in two identical full sets of chromosomes.
Outside of the nucleus are two centrosomes, each containing a pair of centrioles, these structures are critical for the process of cell division. During interphase, microtubules extend from these centrosomes. Prophase I: The copied chromosomes condense into X-shaped structures that can be easily seen under a microscope.
Each chromosome is composed of two sister chromatids containing identical genetic information. The chromosomes pair up so that both copies of chromosome 1 are together, both copies of chromosome 2 are together, and so on. The pairs of chromosomes may then exchange bits of DNA in a process called recombination or crossing over.
At the end of Prophase I the membrane around the nucleus in the cell dissolves away, releasing the chromosomes. The meiotic spindle, consisting of microtubules and other proteins, extends across the cell between the centrioles. Metaphase I: The chromosome pairs line up next to each other along the centre equator of the cell. The centrioles are now at opposites poles of the cell with the meiotic spindles extending from them.
The meiotic spindle fibres attach to one chromosome of each pair. Anaphase I: The pair of chromosomes are then pulled apart by the meiotic spindle, which pulls one chromosome to one pole of the cell and the other chromosome to the opposite pole.
In meiosis I the sister chromatids stay together. This is different to what happens in mitosis and meiosis II. Telophase I and cytokinesis: The chromosomes complete their move to the opposite poles of the cell. At each pole of the cell a full set of chromosomes gather together.
A membrane forms around each set of chromosomes to create two new nuclei.
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