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Class Notes Meiosis Chapter 10: p. 270-276 Questions/Main Idea: Name: _______________________________________ Period:_______________________________________ Date: _______________________________________ Notes: What controls each characteristic or “trait” in an organism? What is a gene? Gene- How many genes are on each of your chromosomes? What are homologous chromosomes? Homologous chromosomes- How many chromosomes do humans have? What is the difference between haploid and diploid cells? Haploid – Diploid -- What are gametes? What is meiosis? meiosis- What does meiosis produce? What happens in interphase, before meiosis? For each of the following stages of mitosis, describe what happens, and draw a diagram: PROPHASE I METAPHASE I ANAPHASE I TELOPHASE I PROPHASE II METAPHASE II ANAPHASE II TELOPHASE II What is the end result of meiosis? What type of cell division do cells use in asexual reproduction? What is the importance of meiosis in terms of sexual reproduction? Compare mitosis and meiosis. Class Notes Meiosis Chapter 10: p. 270-276 Questions/Main Idea: Name: _______________________________________ Period:_______________________________________ Date: _______________________________________ Notes: What controls each characteristic or “trait” in an organism? The instructions for each trait are located in genes, which are segments of DNA on a chromosome. What is a gene? Gene- A gene is a segment of DNA that controls the production of one particular protein. (one gene = instructions for one protein) How many genes are on each of your chromosomes? Each chromosome contains hundreds of genes What are homologous chromosomes? Homologous chromosomes- a pair of matching chromosomes, one from each parent, that carries genes for the same traits. How many chromosomes do humans have? 46 chromosomes, or 23 pairs (one from mom and one from dad for each of the 23 pairs) What is the difference between haploid and diploid cells? Haploid – refers to having half the number of chromosomes as a normal cell. (one copy of each chromosome) (“n” refers to the number of chromosomes in a cell – for humans, n = 23) Diploid – refers to having 2 copies of each chromosome (one from mom and one from dad) (“2n” = 46) What are gametes? Gametes are sex cells (eggs and sperm). They contain half the number of chromosomes of a normal cell What is meiosis? meiosis- a type of cell division that reduces the number of chromosomes by half What does meiosis produce? Gametes or sex cells. What happens in interphase, before meiosis? For each of the following stages of mitosis, describe what happens, and draw a diagram: PROPHASE I METAPHASE I ANAPHASE I Cells carry out normal cell function (metabolism) and replicate DNA Homologous chromosomes pair up Crossing over occurs! (this is important!! – pieces of the homologous chromosome pairs switch places. This allows the exchange of genetic information) Spindles form Spindle fibers attach to centromeres Homologous pairs of chromosomes line up together at the equator Homologous chromosomes separate and move to either side of the cell. (NOT sister chromatids – the entire chromosome!) The cell goes from diploid to haploid (chromosome number is reduced from 2n to n) TELOPHASE I PROPHASE II Homologous chromosomes (consisting of 2 sister chromatids) reach the cell’s opposite poles. Each pole contains only one of the original pair of homologous chromosomes) The sister chromatids that are still attached might not be identical to each other because of the crossing over, or exchange of genetic information that occurred in Prophase I Chromosomes relax or uncoil in the 2 new nuclei. Cytokinesis occurs and the cell does NOT enter interphase, or replicate its DNA again ***The following stages occur in BOTH of the cells that resulted in the division in Meiosis I) Spindle forms and chromosomes condense. METAPHASE II Chromosomes line up at the equator ANAPHASE II Centromeres split and sister chromatids move to opposite poles TELOPHASE II Nuclei form around the 4 chromosomes What is the end result of meiosis? The result of meiosis is 4 genetically different haploid cells What type of cell division do cells use in asexual reproduction? Mitosis – end result is 2 identical haploid gametes What is the importance of meiosis in terms of sexual reproduction? Meiosis provides genetic variation. The 4 resulting haploid cells are all genetically different because of crossing over and random assortment. When sperm and egg join to form a new organism, there is genetic variability. Compare mitosis and meiosis. Mitosis – 2 genetically identical diploid body cells Meiosis – 4 genetically different haploid sex cells