Meiosis notes section 11-4

Meiosis

Chapter 11 Sec. 11-4

Chromosome

-Normal body cell is diploid (2N), meaning it has 2 sets of complimentary chromosomes, each one originating from Mom and Dad.

- They are said to be homologous.

-The egg and sperm from Mom and Dad are haploid (1N), meaning they contain one half of the normal body cell number.

-Meiosis cuts the chromosome number in half to produce gametes.

Meiosis I

-Each chromosome is replicated, like in mitosis

-Each chromosome pairs with its homolog to form a tetrad.

-Crossing over occurs (exchange of genetic material).

-Homologous chromosomes separate and form to new daughter cells.

Meiosis II

-No DNA replication occurs

-Each cell’s chromosomes are made of 2 chromatids that line up in the center.

-The chromatids separate and each new cell that forms is now haploid.

Gamete Formation

-Starts with diploid cells (germ line cells), but end with haploid cells that are genetically different from the diploid cell it started from.

-In sperm or pollen, all 4 new cells are viable.

-In egg formation, one egg cell is viable, the other 3 (polar bodies) disintegrate.