MEIOSIS AND SEXUAL REPRODUCTION

MORE GENETICS VOCABULARY!

sexual reproduction-requires two different parent cells and produces offspring that are genetically different from each parent

homologous chromosomes-a pair of chromosomes that are the same size and shape, and carry alleles for the same trait

homologous mates-duplicated pairs of homologous chromosomes

haploid-having a single stranded chromosome from each pair of homologous chromosomes (n)

eg.male sperm cells

female ova

diploid-having double stranded chromosomes that make up an homologous chromosome pair

eg. all somatic (body) cells like skin, etc.

tetrad-2 pairs of double stranded chromosomes, or 4 chromatids

Meiosis- aka reduction division, cell division in diploid cells that result in haploid cells.

-meiosis is divided into two parts

Stages of Meiosis I

Interphase-same as in mitosis, cell growth and duplication of chromosomes

Prophase I-a diploid set of chromosomes-(2n) duplicated to produce two sets of diploid chromosomes-2(2n), but pairs do not separate

-pairs line up with their homologous mates to form a tetrad,

-this pairing process is called a synapsis

Metaphase I-centromeres of unseparated tetrads line up on the equator of the cell

Anaphase I- homologous pairs separate in a process called disjunction

-diploid set of homologous pairs move to opposite poles of the cell

Telophase I-end of meiosis I, the cytoplasm divides

-daughter cells have half the original amount of chromosomes

MEIOSIS I, RECAP:

counting chromatids

2n DUPLICATED TO 4n WHICH DIVIDE INTO 2(2n)

Meiosis II-exactly like mitosis, except two cells involved simultaneously

No Interphase II

Prophase II-daughter cells form spindles and double stranded chromosomes move toward the cells equator

Metaphase II-centromeres of double stranded chromosomes line up at the cells equator

Anaphase II-centromeres divide and 2 chromatids separate and move toward opposite poles of the cell

Telophase II-both diploid cells (2n) divide, forming 4 haploid cells (n)

-all cells return to resting stage (G1) of cell division cycle

MEIOSIS II, RECAP:

counting chromatids

2(2n) DIVIDE INTO 4(n)

MEIOSIS CHROMOSOME ACCOUNTS

Counting chromatids not chromosomes

2n

DUPLICATE TO 4n

WHICH DIVIDE INTO 2(2n)

WHICH DIVIDE INTO 4(n)

Synapsis-

Process by which genetic material is exchanged (during Prophase I of meiosis) between homologous pairs of chromosomes.