Meiosis Forming haploid cells for sexual reproduction

Interphase

Crossing Over Prophase

Prophase 1 Chromosomes ____________. Chromosomes ____________. Nuclear membrane ___________. Nuclear membrane ___________. Centrioles move and spindles form Centrioles move and spindles form condense disappears

Prophase 1 cont. _________ occurs: pairing of homologous chromosomes (pair of the same type of chromosome but one from each parent) _________ occurs: pairing of homologous chromosomes (pair of the same type of chromosome but one from each parent) Forms a ______: 4 sister chromatids Forms a ______: 4 sister chromatids _____________ occurs: portions of chromatids may break off and reattach on adjacent chromatids _____________ occurs: portions of chromatids may break off and reattach on adjacent chromatids Synapsis tetrad Crossing-over

Crossing over

Metaphase and Anaphase

Metaphase 1 and Anaphase 1 Homologous pairs line up at the equator Homologous pairs line up at the equator Spindle fibers attach to the _____________ of each homologous pair Spindle fibers attach to the _____________ of each homologous pair Homologous pairs split and move to _______ _____ Homologous pairs split and move to _______ _____ centromere opposite poles

Telophase and Cytokinesis

Telophase 1 _____________reach opposite poles of the cell _____________reach opposite poles of the cell ___________ occurs: the cell divides. ___________ occurs: the cell divides. The resulting cells are ______, (2n). The resulting cells are ______, (2n). Chromosomes Cytokinesis diploid

Prophase 2 Centromeres of _____ ________ attach to spindle fibers. Centromeres of _____ ________ attach to spindle fibers. Nuclear membrane__________. Nuclear membrane__________. sister chromatids disappears

Prophase 2

Metaphase 2 _____ __________ line up on the equator _____ __________ line up on the equator Sister chromatids

Metaphase 2

Anaphase 2 Chromatids separate and move to _______ ______ of the cell. Chromatids separate and move to _______ ______ of the cell. opposite poles

Anaphase 2

Telophase 2 ______ __________ forms around the chromosomes. ______ __________ forms around the chromosomes. The cells divide by _________. The cells divide by _________. The resulting 4 cells are ________, (n). The resulting 4 cells are ________, (n). These reproductive cells are called _______. These reproductive cells are called _______. Nuclear membrane cytokinesis haploid gametes

Telophase and Cytokinesis

Meiosis The process of nuclear division that produces haploid cells with half the number of chromosomes as the original diploid cell. The process of nuclear division that produces haploid cells with half the number of chromosomes as the original diploid cell.

Why have meiosis? Results in genetic variation in the new offspring. Results in genetic variation in the new offspring.

Diagram of Meiosis Diploid cell (2n) Haploid cell (n)

More sources of genetic variation: 1. Crossing-over: In prophase 1, when homologous chromosomes exchange genetic information In prophase 1, when homologous chromosomes exchange genetic information 2. Random fertilization: A sperm and egg unite, forming a zygote. A sperm and egg unite, forming a zygote.

Only germ cells undergo meiosis to produce haploid reproductive cells. Only germ cells undergo meiosis to produce haploid reproductive cells. What are germ cells

What are somatic cells? All other cells in the body are somatic cells. Normally diploid. All other cells in the body are somatic cells. Normally diploid.

Gamete development Gametes are only formed in specialized reproductive organs in an organism. Gametes are only formed in specialized reproductive organs in an organism. Spermatogenesis: formation of sperm cells. Spermatogenesis: formation of sperm cells.

Oogenesis: formation of egg cells. A parent cell produces only 1 mature egg, which receives most of the cytoplasm. The other 3 cells are called polar bodies and they degenerate. Oogenesis: formation of egg cells. A parent cell produces only 1 mature egg, which receives most of the cytoplasm. The other 3 cells are called polar bodies and they degenerate.

Let’s Review 1. What are homologous chromosomes? 2. What happens to homologous pairs during metaphase 1? 3. How many chromosomes are in a cell at the end of telophase 1? 4. How many chromosomes are in a cell at the end of telophase 2?