BIOLOGY Unit 4 Notes: Meiosis

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Presentation transcript:

BIOLOGY Unit 4 Notes: Meiosis

(1) What is Meiosis? Cell division for sex-cells. Sex Cells: Are also called Gametes. Sperm in Males Eggs in Females

(2) What happens during Meiosis? There are 2 divisions. Start with 1 cell and end up with 4 genetically unique cells. Start “2n” or “Diploid”  End “1n” or “Haploid” 1n = Haploid = ½ Set of Genetic Information In Humans that means that each sperm or egg cell should have 23 chromosomes.

(3) Meiosis Phases Meiosis-1: Meiosis-2: Start with 1 cell and end with 2 Prophase, Metaphase-1, Anaphase-1, Telophase-1, Cytokinesis-1 Crossing Over occurs Homologous Pairs of Chromosomes Meiosis-2: Start with 2 cells and end with 4 Metaphase-2, Anaphase-2, Telophase-2, Cytokinesis-2 Pairs of Sister Chromatids Law of Independent Assortment Law of Segregation

(4) Meiosis-1 Details Prophase: Chromosomes form + Nucleus dissolves. Metaphase-1: Homologous pairs of chromosomes line up at the metaphase plate. Crossing Over occurs. Anaphase-1: Homologous pairs of chromosomes separate. Telophase-1: Chromosomes are fully separated. Cytokinesis-1: Cytoplasm splits and the cell membranes divide.

(5) Meiosis-1 Vocabulary: Homologous Pairs of Chromosomes  Pairs of sister chromatids with similar segments of DNA (or genes.) Looks like 2 X’s. Crossing Over  When nearby chunks of DNA are exchanged between homologous pairs of chromosomes. Used to increase genetic diversity.

(6) Meiosis-2: Metaphase-2: Pairs of sister chromatids line up at the metaphase plate. Anaphase-2: Pairs of sister chromatids separate. Law of Segregation. Law of Independent Assortment. Telophase-2: Chromosomes are fully separated. Nuclei reform. Cytokinesis-2: Cytoplasm splits and the cell membranes divide up.

(Drawing Time)

(7) Meiosis-2 Vocabulary: Sister Chromatids: Identical copies of chromosomes. Law of Segregation: Chromosomes split up so that each sex cell receives a different variation of each gene. Law of Independent Assortment: Chromosomes split up completely independent of every other chromosome and gene variation.

(Drawing Time)

(8) Meiosis Errors When chromosomes do not separate correctly during meiosis this can cause: Sex Cells to have too many chromosomes (more than 23). Sex cells to have too few chromosomes (less than 23). Individuals born from these sex cells will acquire a genetic disorder from having the wrong number of sex chromosomes.