How many bivalents are formed in a cell with 20 chromosomes at the beginning of meiosis i?

Answer

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Hint: Mitosis and meiosis are two methods of cell division found in humans and other animals. The end product of mitotic division is two clones of the parent cell whereas that of meiosis is four gametes with half the number of chromosomes the parent cell has.

Complete answer:

If an organism has 20 chromosomes, then the number of chromosomes the daughter cells have after mitosis is 20 because when a cell divides by the process of mitosis it produces two clone daughter cells having the same number of chromosomes (20) as the parent cell has. When an organism with 20 chromosomes undergoes meiotic division it produces four gametes each having half the number of chromosomes(10) the parent cell has.1. Mitosis: where a parent cell divides into two daughter cells each of which is genetically just like the parent cell. Mitosis is also known as vegetative cell division. It occurs in several stages, they are-(a) Prophase- Here the chromatin condenses into discrete chromosomes. Then the nuclear membrane breaks down and spindles start forming at opposite poles of the cell.(b) Metaphase-At this stage the spindle reaches maturity and chromosomes align at the equator.(c) Anaphase- paired chromosomes separate and start moving to poles. Spindle fibers are not connected to chromatids. At the top of the anaphase, each pole contains an entire compilation of chromosomes.(d) Telophase- The chromosomes begin to condense two new nuclei form, one for every set of chromosomes.Cytokinesis- Cytokinesis may be a sort of division of the cell's cytoplasm. The process of cytokinesis starts before the end of mitosis in anaphase and completes shortly after telophase/mitosis. At the top of cytokinesis, two genetically identical daughter cells are produced. These are diploid cells and each cell is having a complement set of chromosomes.2. Meiosis: It is the division of a cell in two stages that results in four daughter cells, each with half the chromosomes of the original cell. Meiosis is also known as reproductive cell division. Meiosis I and Meiosis II are two stages of meiosis. Meiosis I involves-(a) Prophase I- In this phase, chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossover occurs.(b) Metaphase I- Spindle fibers from opposing centrosomes hook up with bivalents (at centromeres) and align them along the center of the cell.(c) Anaphase I- During anaphase l the spindle fibers contract, the bivalent, homologous chromosomes split and move to opposite poles of the cell.(d) Telophase I- Chromosomes condense, the nuclear membrane may reform, the cell divides (cytokinesis) to make two haploid daughter cells.Meiosis II involves-(a) Prophase II- Here chromosomes condense, nuclear membrane dissolves, and centrosomes move to opposite poles.(b) Metaphase II- Activities same as Prophase ll but in a more advanced way.(c) Anaphase II- Now the spindle fibers start contracting and sister chromatids are separated, now the chromatids are called chromosomes and move to opposite poles.(d) Telophase II- During this stage the chromosomes decondense, nuclear membrane reforms, cells divide by cytokinesis to make four haploid daughter cells.

Note:

-The cell was discovered by Mr. Robert Hooke in 1665. It consists of a cytoplasm that contains proteins and nucleic acid and is enclosed within a membrane called the cell membrane. -Meiosis I include crossing over or recombination of genetic material between chromosome pairs.-Meiosis II maintains the number of chromosomes in each cell and it starts with two haploid parent cells and ends with four haploid daughter cells.