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Meiosis and Genetic Diversity: Summary Notes
Meiosis and Genetic Diversity: Summary Notes
Heredity and Genetics
Heredity: Transmission of traits from one generation to the next.
Traits are passed through genes (segments of DNA).
Offspring inherit chromosomes, acquiring genes from parents.
Asexual vs. Sexual Reproduction
Asexual: Single parent, offspring are clones, variation only through mutations.
Sexual: Two parents, offspring have unique gene combinations, genetic variation.
Homologous Chromosomes
Pairs of chromosomes with same size, length, and centromere position.
One chromosome inherited from each parent.
Karyotypes
Display of chromosome pairs ordered by size and length.
Cells and Chromosomes
Somatic (body) cells: Diploid (2n), two sets of chromosomes (e.g., humans 2n = 46).
Gametic (sex) cells: Haploid (n), one set of chromosomes (e.g., humans n = 23).
Autosomes: Non-sex-determining chromosomes (22 pairs in humans).
Sex chromosomes: X and Y (Eggs: X, Sperm: X or Y).
Life Cycles
Sequence of reproductive stages from conception to reproduction.
Fertilization (haploid sperm + haploid egg = diploid zygote) alternates with meiosis.
Meiosis
Process creating haploid gamete cells in diploid organisms.
Results in daughter cells with half the chromosomes (e.g., human diploid 2n=46 -> haploid n=23).
Involves two rounds of division: Meiosis I and Meiosis II.
Mitosis vs. Meiosis
Mitosis: Somatic cells, 1 division, 2 diploid cells, identical daughter cells.
Meiosis: Gametes, 2 divisions, 4 haploid cells, genetically unique daughter cells.
Key Events in Meiosis
Prophase I: Synapsis and crossing over.
Metaphase I: Tetrads line up at metaphase plate.
Anaphase I: Homologous pairs separate.
Meiosis I
Prophase I: Synapsis (homologous chromosomes pair) and crossing over (DNA exchange).
Metaphase I: Tetrads align at metaphase plate with independent orientation.
Anaphase I: Homologous chromosomes separate; sister chromatids remain attached.
Telophase I & Cytokinesis: Nuclei and cytoplasm divide, resulting in haploid cells.
Meiosis II
Prophase II: Spindle forms; no crossing over.
Metaphase II: Chromosomes line up at metaphase plate.
Anaphase II: Sister chromatids separate.
Telophase II & Cytokinesis: 4 haploid cells, genetically unique.
Genetic Variation in Meiosis
Crossing Over: Produces recombinant chromosomes.
Independent Assortment: Random chromosome orientation at metaphase I.
Random Fertilization: Any sperm can fertilize any egg.
Summary
Meiosis and fertilization ensure genetic diversity, which drives natural selection.
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Chapter 3: Using Research Methods
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