Meiosis is Necessary for Sexual Reproduction3 Sexual Reproduction –

Meiosis I3 Prophase I –2 Metaphase I –2 Anaphase I –2 Telophase I –

Meiosis II2 Prophase II –2 Metaphase II –2 Anaphase II –2 Telophase II –

4 The Why and Where of Meiosis -

LEARNING GOAL 2RELATE THE PROCESS OF MEIOSIS TO

THE INHERITANCE OF GENETIC TRAITS.

Unit IVGenetics

Meiosis is Necessary for Sexual Reproduction

Sexual ReproductionReproductive method of most plants and animals.Gametes (sex cells) from opposite sexes unite to form a zygote (fertilized egg).A zygote is a diploid cell (full chromosome set) so the number of chromosomes in the gametes must be half (haploid).Meiosis results in gamete production.

Meiosis IProphase I

Same as prophase of mitosis except chromosomes form homologous pairs. Homologous means that the chromosomes contain genes for the same traits and one member of the pair came from the mother and one from the father.Homologs may exchange sections of chromosomes at this stage which is called crossing over.

Metaphase I

Homologous pairs move to center of cell.

Each homolog still consists of two chromatids.

Anaphase I

Homologs separate.

Chromatids of each homolog stay together.

Telophase I

Chromosomes gather at opposite poles of cell, then cytokinesis occurs.

Each cell now has half the original number of chromosomes.

Meiosis II

Same as mitosis.Prophase IIChromosomes are

still doubled and become visible.

Metaphase II

Replicated chromosomes line up in the middle.

Anaphase II

Sister chromatids are pulled apart at the centromeres.

Telophase II

Chromosomes gather at opposite polesNuclear membrane reformsCell divides

The Why and Where of Meiosis Results in the production

of male and female gametes (sperm and egg).

Produces haploid cells so that the diploid number can be restored upon fusion of gametes during fertilization.

Occurs in cells of the reproductive organs, testes in males and ovaries in females.

Creates genetic variation due to crossing over and shuffling of homologous chromosome pairs.