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Lecture 5

BIO152H5 Lecture 5: BIO152 - Lecture 5 - Meiosis and Sexual Reproduction

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Maria Arts

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BIO152 Hadia Saeed May 18 2017 Meiosis: Sexual Reproduction Chromosomes Meiosis: There are 23 types of chromosomes and 2 chromosomes of each type Homologous chromosomes: one from each parent X Y are sex chromosomes Humans: 2n=46 Meiosis Sexual Reproduction: Two haploid gametes one from each parent unite in fertilization to form a genetically unique, diploid zygote Explaining meiosis; o Proximate? How? o Ultimate? Why? Meiosis: o Sexual reproduction: Involves the alternation of meiosis fertilization Major Events in Meiosis: a) each chromosome replicates prior to undergoing meiosis b) during meiosis, chromosome number in each cell is reduced o Four daughter cells contain one chromosome each c) a full complement of chromosomes is restored during fertilization When Do Meiosis Fertilization Occur During the Life of an Organism? Multicellular diploid> meiosis Haploid spores break into half Alternation generation occurs here > haploid gamete More complex than life cycle in animals Phases of Meiosis: Has two divisions Meiosis I Meiosis II Meiosis I is a continuous process o Interphase Chromosomes replicate in parent cell, in uncondensed state (look in lec) o Prophase (early late prophase) Early Prophase I: chromosomes condense, nuclear envelope breaks up, spindle apparatus forms. Synapsis of homologous chromosomes Late Prophase I: Crossing over of nonsister chromatids (often multiple crossovers bw the same chromatids) *Very Important* o Metaphase Tetrads migrate to metaphase plate, homologous chromosomes line up in the middle o Anaphase Homologs separate and begin moving to opposite sides of cell o Telophase I Cytokinesis Chromosomes move to opposite sides of the cell, then cell divides We start off with 4 chromosomes and end up with 2 > haploid
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