Mrs. Stewart Biology I standard MITOSIS VS. MEIOSIS Mrs. Stewart Biology I standard

REVIEW: Cell Cycle Mitosis Interphase M-phase (mitosis) G1, S, and G2 M-phase (mitosis) P-M-A-T-C Mitosis Asexual reproduction Produces 2 identical daughter cells Daughter cells are diploid Daughter cells are identical to parent/mother cell

What differences can you see? How many sets of chromosomes are in the cells that Meiosis produces? How many cells does Meiosis produce? How many divisions occur in Meiosis?

MEIOSIS: The process of creating a gamete

Chromosomes come in matching sets -these are called homologous pairs

Karyotype after DNA replication Notice how each chromosome has duplicated itself.

Final Products: Mitosis Meiosis Somatic cells in your body have two sets of chromosomes - they are called DIPLOID   Gametes (Sex cells-sperm and eggs) only have one set (half) of chromosomes  - they are called HAPLOID

What are the steps? Phases of Meiosis I Interkinesis Prophase I Metaphase I Anaphase I Telophase I Cytokinesis Interkinesis Phases of Meiosis II Prophase II Metaphase II Anaphase II Telophase II

Interphase Makes the diploid (2n) cell now be (4n) DNA replicates Makes the diploid (2n) cell now be (4n) n=number of chromosome sets/pairs Example: humans have 46 total chromosomes, so our diploid number is 2n or 2(23) where n = 23

Prophase I Homologous chromosomes pair up (forming a tetrad) - Mom & Dad go on a date Crossing over occurs Chromatids MAY exchange portions of DNA Leads to genetic variances

Telophase I and Cytokinesis Metaphase I Spindle fibers attach to the chromosomes Homologous chromosomes line up in the middle of the cell Anaphase I Fibers pull the homologous chromosomes toward opposite ends of the cell Telophase I and Cytokinesis Nuclear membranes form Cell separates into two new cells

Meiosis II The daughter cells from Meiosis I divide again WITHOUT replicating their chromosomes That leads to 4 gametes, each with half the number of chromosomes (haploid) as the original “mother” cell

Telophase II and Cytokinesis Metaphase II Spindle fibers attach to the chromosomes chromosomes line up in the middle of the cell – similar to how they do in Mitosis Anaphase II Fibers pull the sister chromatids toward opposite ends of the cell Telophase II and Cytokinesis Nuclear membranes form Both cells separate – forming 4 new haploid cells

Oogenesis – meiosis in human female reproductive cells – makes eggs (ovum) Forms one egg cell with a large supply of stored nutrients. The other 3 gametes produced, called polar bodies, disintegrate.

Produces 4 viable gametes Spermatogenesis – meiosis in human male reproductive cells to make sperm (spermatazoa) Produces 4 viable gametes All 4 gametes produce a long whip-like tail

Meiosis: Cell division necessary for sexual reproduction Produces 4 daughter cells Daughter cells are Haploid Daughter cells are gametes (sexual repro. cells) 2 nuclear/cellular divisions Vital to maintain correct number of offspring in sexually reproducing organisms Crossing over = opportunity for genetic variability

Differentiate Mitosis Meiosis Used for sexual reproduction Produces 4 daughter cells Daughter cells are Haploid Daughter cells are genetically different from each other, and from parent cell Produces gametes Two nuclear/cellular divisions Asexual reproduction Produces 2 daughter cells Daughter cells are diploid Daughter cells are identical to each other and to parent cell Produces somatic cells One cell/nuclear division

Human chromosomal diseases Down’s syndrome (extra chromosome #21) Turner’s syndrome (missing or incomplete X chromosome in girls) Klinefelter’s syndrome (males that have an extra X chromosome [XXY]) **Mistake in meiosis can lead to an incorrect chromosomal number, causing consequences for offspring**

Video Meiosis square dance