Mitosis+and+Meiosis

Growth, repair and reproduction require cells to divide. There are two types of cell division: mitosis and meiosis.

Mitosis is the type of cell division used for growth and repair (or maintenance). It occurs in most cells in the body. Its primary function is to ensure that each of the resulting cells has an identical copy of all the DNA that is found in the nucleus. In most humans cells, the DNA exists in 46 separate molecules called chromosomes. 23 of the chromosomes are from the mother, 23 are from the father. Mitosis makes sure that each daughter cell gets a copy of each chromosome.

Meiosis is the type of cell division used for sexual reproduction. It is how sperm and egg are produced. It ensures that sperm and egg only have 23 chromosomes each so that when fertilization occurs, the resulting zygote will have 46 chromosomes. Humans have 23 different chromosomes. An individual has one of each chromosome from each parent. That means people have 23 pairs of chromosomes for a total of 46.



When the cell is not dividing, it is in INTERPHASE. Interphase consists of three phases: G1, S and G2. See what happens in each phase in the diagram below.



__Mitosis__ Mitosis is an asexual form of cell division. It is a small part of the cell cycle. Mitosis occurs in all the parts of the body as a means of growth and repair. The main function of mitosis is to ensure that each daughter cell receives a copy of the genetic information within the cell.

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Onion Cell Clock Activity

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Meiosis is a special form of cell division that only occurs in the reproductive organs of the testes and the ovaries. It is used to produce sperm and eggs which have half the amount of DNA that most body cells have.
 * Meiosis**

Most cells in the body have two versions of each chromosome, one version from each parent. The two versions of a chromosome which have similar information are known as **homologous** chromosomes. Humans have 23 pairs of homologous chromosomes for a total of 46. 22 of these chromosomes are called somatic chromosomes while 1 pair of chromosomes are the sex chromosomes, usually XX or XY. Body (somatic) cells that have two versions of chromosomes are called **diploid (2n)** while sperm and egg which only contain one version of each chromosome are described as **haploid (1n)**.

During fertilization, one egg and one sperm combine to form a diploid zygote which will develop into an entire organism. The purpose of meiosis is to produce haploid cells which can then combine in sexual reproduction.

During meiosis, cells undergo two rounds of cell division, called meiosis I and meiosis II respectively. Many of the stages are similar to mitosis with a few exceptions.



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