Meiosis Mrs. Harper Biology 11/28/17

November 29, 2017 Download Notes Begin working on Do Now

DO NOW 11/29/17 How many cells are produced during mitosis? Are they genetically different or identical? 3. What type of cells are produced during mitosis? (somatic body cells or sex cells) 4. List the phases of mitosis in the correct order. 5. What occurs during each phase of mitosis? 6. Define cytokinesis.

Division That Produces Sex Cells Meiosis – Division That Produces Sex Cells Why do you share some but not all characters of each parent? What are the rules of this sharing game? At one level, the answers lie in meiosis.

Reduction-Division Genetic Recombination MEIOSIS Reduction-Division Genetic Recombination

Meiosis The form of cell division by which GAMETES or sex cells are produced. GAMETES are sperm or egg cells. Gametes have HALF the # of chromosomes. Haploid- contains half the amount of chromosomes Diploid- contains full set of chromosomes

Meiosis Continued DIPLOID (2n)  HAPLOID (n) Meiosis is involved in SEXUAL reproduction. TWO divisions (MEIOSIS I and MEIOSIS II).

Interphase Cell grows and DNA replicates Occurs before meiosis I, but not meiosis II Cell grows and DNA replicates

Meiosis I Cell division that reduces the chromosome number by one-half.

Homologous Chromosomes Pair of chromosomes (maternal and paternal) that are similar in shape and size. Homologous pairs (tetrads) carry GENES controlling the SAME inherited traits. Humans have 23 pairs of homologous chromosomes: First 22 pairs are autosomes 23rd pair is sex chromosomes

Homologous Chromosomes eye color locus hair color Paternal Maternal

Sex Chromosomes XX chromosome - female XY chromosome - male

MEIOSIS I Homologs separate Meiosis I

Prophase I Nuclear envelope disappears/Chromosomes coil Synapsis (pairing) occurs Tetrads form & Crossing over occurs centrioles spindle fiber aster fibers TETRAD

Genetic Recombination Tetrad nonsister chromatids chiasmata: site of crossing over variation

Metaphase I Homologous chromosomes line up in the middle. Independent assortment occurs – chromosomes separate randomly

Anaphase I Homologous chromosomes pull apart. Sister chromatids remain attached

Telophase I Each nucleus has haploid set of chromosomes. Cytokinesis occurs & two haploid daughter cells are formed.

Sister Chromatids Separate MEIOSIS II Sister Chromatids Separate Meiosis II

Meiosis II No Interphase II No DNA Replication Meiosis II is similar to mitosis

Prophase II Same as Prophase in mitosis Chromosomes condense & Spindle forms

Metaphase II Same as Metaphase in mitosis Chromosomes line up in the middle

Anaphase II Same as Anaphase in mitosis SISTER CHROMATIDS pull apart

Telophase II Same as Telophase in mitosis. Nuclei reform CYTOKINESIS occurs. Final product of meiosis: FOUR HAPLOID daughter cells that are all genetically different Called GAMETES (eggs and sperm)

Meiosis Video https://www.youtube.com/watch?v=D1_-mQS_FZ0 Or https://www.youtube.com/watch?v=-kl94jqlIs0

Assignment Complete the worksheet silently and independently on CODE RED Unfinished classwork is homework