Meiosis

Meiosis

Somatic cells undergo Mitosis Gametes or sex cells undergo meiosis,

resulting in a cell with half of the usual number of chromosomes (compared to a somatic cell).

So we say that meiosis results in a halving of the chromosome number. Mitosis is just copying the DNA exactly as it is.

Meiosis One chromosome duplication Two cellular divisions Yield : 4 haploid cells

Mitosis One chromosome duplication One cellular division Yield : 2 diploid cells

Meiosis I

Homologous chromosomes line up at the medial line, then separate as whole chromosomes

Anaphase II Telophase IIThe sister chromatids separate in Anaphase II.

Crossing Over

Prophase I A process, occurring during meiosis, in

which, homologous chromosomes exchange reciprocal portions of themselves.

Similar to shuffling of a deck of cards.

Crossing Over

Independent Assortment

The random distribution of chromosome pairs during meiosis.

8 million different combinations of chromosomes lining up in Metaphase I.

Meiosis generates diversity, mitosis does not

Gamete production in Humans

Spermatogonium produce sperm Half of the sperm carry an X chromosome Half of the sperm carry a Y chromosome Sperm ‘travel light’ (Chromosomes,

mitochondria, flagella) Oogonium

Produce one egg, three polar bodies All the cytoplasm is put into the egg All oogonia are present at birth

Sperm

Asexual Reproduction

Not all reproduction involves two reproductive cells. Asexual reproduction Vegetative reproduction Regeneration Self-fertilization Hermaphrodites

Fertilization restores the diploid condition