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Meiosis Notes

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Biological Sciences
BIOSC 0160
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1/14 Chapter 12: Meiosis Types of Reproduction • Asexual Reproduction o One parent only o Parent passes all of its genes to offspring o Offspring are virtually identical to parent and each other (barring genetic mutation) • Sexual Reproduction o Two parents o Each passes half of its genes o Offspring differ from parents and each other, though they may show resemblance • Parthenogenetic Reproduction o Egg develops without being fertilized Life Cycle • Sequence of stages and events in the reproductive history of an organism • From fertilization to reproduction • Chromosomes o Homologous “basic” chromosomes  Same length, centromere position, and gene order  NOT sister chromatids; homologs are NOT identical • Karyotypes: Complete set of chromosomes in an organism or cell or a photograph • Autosomes: non-sex chromosomes 1/14 • Sex Chromosomes: sex determination o Non-homologous: X and Y o Homologous: X and X Ploidy • Ploidy: number of each basic chromosome in an organism’s cells • Haploid: n, possession of only one of each basic chromosome • Diploid: 2n, possession of two of each basic chromosome 1/14 Meiosis • Specialized form of cell division • Associated with sexual reproduction/gamete formation o Reduction from diploid to haploid o Haploid gametes join at fertilization and reconstitute the diploid condition • Meiosis I: separates homologs o Interphase  Chromosomes replicate  Centrosome replicates o Prophase I  Nuclear envelope fragments  Chromosomes condense  Homologs synapse • Creates tetrad of four chromatids  Crossing over occurs (called chiasmata) 1/14 • Exchange genetic information with homolog  Spindle apparatus form
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