Meiosis and Sexual Life Cycles

What is meiosis?

--> cell division that produces reproductive cells in sexually reproducing organisms (the nucleus divides into four hapoloid cells/nuclei)

What are the stages of meiosis?

meiosis I: prophase I, metaphase I, anaphase I, telophase I and cytokinesis (division of the cytoplasm)

meiosis II: prophase II, metaphase II, anaphase II, telophase II and cytokinesis

What are the differences between mitosis and meiosis?

Basically, meiosis reduces the number of chromosome sets from two (diploid) to one (haploid), whereas mitosis conserves the number of chromosome sets. Therefore, meiosis produces cells that differ genetically from their parent cell and from each other, whereas mitosis produces daughter cells that are genetically identical to their parent cell and to each other.

Facts:

- We inherit one set of chromosomes from our mother and one from our father

- In sexual reproduction, a single parent produces genetically identical offspring by mitosis

- Normal human somatic cells have 46 diploid chromosomes.

- The two cell divisions of meiosis produce 4 haploid daughter cells.

- Mutations are the original source for genetic variation.

JK Key terms:

Heredity (inheritance) = transmission of traits from one generation to next

Genetics = the scientific study of heredity

Clone = a group of genetically identical individuals

Gametes = reproductive cells

Somatic cells = any cell other than those involved in gamete formation

Karyotype = display of paired chromosomes (map of chromosomes)

Sex chromosomes = x and y, determine the sex

Autosomes = other chromosomes

Diploid cell= any cell with two chromosome sets (2n)

Haploid cell= any cell with a single chromosome set (n)

Summary:

A cell undergoing meiosis will divide two times; the first division is meiosis 1 and the second is meiosis 2. The phases have the same names as those of mitosis. A number indicates the division number (1st or 2nd):

meiosis 1: prophase 1, metaphase 1, anaphase 1, and telophase 1

meiosis 2: prophase 2, metaphase 2, anaphase 2, and telophase 2

In the first meiotic division, the number of cells is doubled but the number of chromosomes is not. This results in 1/2 as many chromosomes per cell.

The second meiotic division is like mitosis; the number of chromosomes does not get reduced.