BIOLOGY-MODULE-11-THE-DIFFERENT-PHASES-OF-CELL-CYCLE-MEIOSIS.pdf

OWNED BY: Necy Luz Español Villamor Dinolan Ayag Lubo DATE: August 22, 2024 LESSON TITLE: THE DIFFERENT PHASES OF CELL CYCLE: MEIOSIS MODULE NUMBER: MODULE 11 LESSON OBJECTIVES: Identify the different phases of the meiotic cell division. Describe the events happening in the different phases of...

OWNED BY: Necy Luz Español Villamor Dinolan Ayag Lubo DATE: August 22, 2024 LESSON TITLE: THE DIFFERENT PHASES OF CELL CYCLE: MEIOSIS MODULE NUMBER: MODULE 11 LESSON OBJECTIVES: Identify the different phases of the meiotic cell division. Describe the events happening in the different phases of the meiotic cell division. MEIOSIS - type of cell division that reduces the chromosome number by half - from Diploid (2n = 46 chromosomes) to Haploid (n = 23 chromosomes). - Only in reproductive cells in sexually reproducing organisms. - Ensures genetic variability and maintains the chromosome number across generations. PHASES OF MEIOSIS (MEIOSIS I & MEIOSIS II) 1. MEIOSIS I (REDUCTIONAL DIVISION): - Reduces chromosome number from diploid (46) to haploid (23). ~ PHASES OF MEIOSIS I: A.) PROPHASE I: Leptonema: Chromosomes become visible after coiling. Zygonema: Homologous chromosomes pair in a process called synapsis, forming a bivalent (two homologous chromosomes consisting of four chromatids). Pachynema: Chromosomes thicken, and crossing-over occurs (exchange of chromosome segments between homologous chromosomes), ensuring genetic variability. Diplonema: Homologous chromosomes begin to separate, and chiasmata (points of crossing-over) are visible. Diakinesis: Chromosomes fully condense; chiasmata move to the ends, and the nuclear envelope breaks down, allowing spindle fibers to form. B.) METAPHASE I - Homologous chromosomes align on the metaphase plate. Spindle fibers attach to chromosomes from opposite poles. C.) ANAPHASE I - Homologous chromosomes separate and move to opposite poles. Unlike in mitosis, sister chromatids remain attached at the centromere. D.) TELOPHASE I: - Homologous chromosomes complete their migration to the poles. The nuclear envelope reforms, and cytokinesis occurs, producing two haploid daughter cells. OWNED BY: Necy Luz Español Villamor Dinolan Ayag Lubo 2. MEIOSIS II (EQUATIONAL DIVISION): - Similar to mitosis, meiosis II separates sister chromatids, maintaining the haploid number (23 chromosomes). ~ PHASES OF MEIOSIS II: A.) PROPHASE II - Spindle apparatus forms again; chromosomes condense and prepare for division. B.) METAPHASE II - Chromosomes align on the metaphase plate. The kinetochores of sister chromatids face opposite poles. C.) ANAPHASE II - Centromeres separate, and chromatids (now individual chromosomes) move to opposite poles. D.) TELOPHASE II: - Nuclear envelopes reform around the separated chromosomes. Cytokinesis occurs, producing four non-identical haploid daughter cells. KEY TERMS & DEFINITIONS: MEIOSIS: A type of cell division that reduces the chromosome number by half, creating four genetically diverse haploid cells from a diploid parent cell. DIPLOID (2n): A cell containing two complete sets of chromosomes (46 in humans). HAPLOID (n): A cell containing one complete set of chromosomes (23 in humans). HOMOLOGOUS CHROMOSOMES: Pairs of chromosomes (one from each parent) that are similar in shape, size, and genetic content. SYNAPSIS: The pairing of homologous chromosomes during meiosis. BIVALENT/TETRAD: A pair of homologous chromosomes (4 chromatids). CROSSING-OVER: The exchange of genetic material between homologous chromosomes, contributing to genetic diversity. CHIASMA: The point where two homologous non-sister chromatids exchange genetic material. OWNED BY: Necy Luz Español Villamor Dinolan Ayag Lubo NONDISJUNCTION: Failure of chromosomes or chromatids to separate properly during meiosis, leading to genetic disorders (Down Syndrome). CYTOKINESIS: - Division of the cytoplasm, completing cell division and resulting in four genetically distinct haploid cells. KEY POINTS TO REMEMBER: 1. Purpose of Meiosis: To reduce chromosome numbers and create genetic diversity through recombination (crossing-over). 2. Meiosis I Vs Meiosis II: - Meiosis I reduces the chromosome number from diploid to haploid. - Meiosis II separates sister chromatids, like mitosis, but in haploid cells. 3. Errors in Meiosis: Nondisjunction and other errors (translocation, deletion) can cause genetic disorders, impacting human health significantly. 4. Crossing-over & Genetic Variability: - Crossing-over during Prophase I is key to introducing genetic variation in offspring, which is a fundamental advantage of sexual reproduction. DIFFERENCES BETWEEN MITOSIS AND MEIOSIS: 1. NUMBER OF CELL DIVISIONS: - Mitosis: 1 - Meiosis: 2 2. NUMBER OF DAUGHTER CELLS: - Mitosis: 2 - Meiosis: 4 3. GENETIC IDENTITY: - Mitosis: Daughter cells are genetically identical to the parent cell. - Meiosis: Daughter cells are genetically different from the parent cell due to crossing-over and independent assortment. 4. CHROMOSOME NUMBER: - Mitosis: Same as parent cell (diploid, 46 chromosomes). - Meiosis: Half of parent cell (haploid, 23 chromosomes). 5. WHERE: - Mitosis: Somatic cells. - Meiosis: Gametes (sex cells). 6. WHEN: - Mitosis: Throughout life for growth and repair. - Meiosis: During sexual maturity for reproduction. 7. ROLE: - Mitosis: Growth, repair, and asexual reproduction. - Meiosis: Sexual reproduction and genetic diversity. OWNED BY: Necy Luz Español Villamor Dinolan Ayag Lubo COMMON ERRORS IN MEIOSIS: NON-DISJUNCTION: Failure of homologous chromosomes or sister chromatids to separate, leading to genetic disorders like: - DOWN SYNDROME: Extra copy of chromosome 21. - KLINEFELTER SYNDROME: Additional X chromosome (XXY). - TURNER SYNDROME: Missing X chromosome in females (XO). OTHER ERRORS: - TRANSLOCATION: A chromosome fragment attaches to a non- homologous chromosome. - DELETION: Loss of a chromosome segment, affecting the genetic material.