Dna, Dna replication, and cell division (mitosis and Meiosis)

MEIOSIS

Key ConceptsMeiosis halves the nuclear chromosome content and generates diversity.Sexual reproduction requires special cells made by meiosis.Sperm and egg are produced by meiosis.

MeiosisThe process of meiosis produces sex cells.

For almost all types of animals, two parents are needed for reproduction: a male and a female. Most plants use this form of reproduction as well.Body cells are reproduced through mitosis. However, there is another type of cellular reproduction. This type of reproduction is called meiosis.

3MEIOSIS-division of one cell into haploid gametes.GAMETE-sex cells (egg or sperm).Cell divides twice.Result: cells with the number of chromosomes (haploid).2 Parts:MEIOSIS I-original cell divides into 2 cells; separates the chromosomes from homologous pairsProphase I, Metaphase I, Anaphase I, Telophase IMEIOSIS II-cells made in Meiosis I are split into 2 new cells each; separates chromatids.Prophase II, Metaphase II, Anaphase II, Telophase II

Explore this animation about meiosis

When mitosis is completed, each new cell's chromosome number remains the same as in the original parent cell (diploid).

When meiosis is completed, each sex cell's chromosome number is half (haploid) the original number. The new sperm and egg cells have half the number of chromosomes that are found in a normal body cell.

5Meiosis - FYITake a look at a family with more than one child. You can see that the children are different from each other, even though they have the same parents.

Meiosis is the process of mixing genetic material and preparing it for the sex cells necessary for sexual reproduction.

6Meiosis - FYIThe joining of these two sex cells, or gametes (sexual reproduction) is very important for the survival of living things.

It also plays a significant role in evolution.

7With the exception of identical twins, children in the same family are never exactly alike.

Why is this so, if the children were born of the same parents?

The explanation arises from one of the two important jobs of meiosis.

The first job of meiosis is to maintain the normal species chromosome number by producing gametes that have single sets of chromosomes.FYI

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The second important job of meiosis is to increase genetic variability among offspring by recombining genes in the eggs and sperm.

Genes may get exchanged between chromosomes during meiosis in a process called crossing-over.

Also, chromosomes may get resorted into new groupings.FYI

Emmett Smith and Family Dallas CowboysThis genetic variation among offspring is what natural selection acts on. A greater variety of characteristics in offspring increases the chances that some individuals will be better suited than others to survive in a particular place and time. As natural selection acts on the varied offspring within a population, generation after generation, the species evolves.9

Because of genetic recombination during meiosis, sexual reproduction results in offspring that are different from each other and from their parents.FYI

10MORE GENETIC DIVERSITYDuring Prophase I, the homologous chromosomes will pair up to form TETRADS-pairs of homologous chromosomes.Portions of the chromosomes (within the pair) may break off and switch with the corresponding piece in the tetrad (swap parts).CROSSING OVER-chromosomes in tetrad swap corresponding pieces or sections.GENETIC RECOMBINATION-putting new combinations of genes together.

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