Cell Cycle and Cell Divisions Lecture 9 PDF

Eukaryote chromosomes - Eukaryote chromosomes come in pairs - Normal humans have 46 chromosomes in 23 pairs - One chromosome of each pair comes from an individual's mother, the other comes from their father - Autosomes: Found in both males and females - In humans there are 22 pair...

Eukaryote chromosomes - Eukaryote chromosomes come in pairs - Normal humans have 46 chromosomes in 23 pairs - One chromosome of each pair comes from an individual's mother, the other comes from their father - Autosomes: Found in both males and females - In humans there are 22 pairs of autosomes - Autosomes that are the same size (& structure) are called homologues  Sex Chromosomes: Determine an individual's gender - One pair of chromosomes (X and Y) - The X and Y chromosomes are not homologous - The X chromosome is much larger than the Y chromosome and contains many genes - The Y chromosome has only a small number of genes - In humans and other mammals females are XX and males are XY Human Karyotype Human Sexual Cycle Chromosome Sorting ================== - - - - Cell Division ============= Chromosomes, Eukaryote ====================== Chromosomes vs. Chromatin ------------------------- ### Chromosomes - Tightly packaged DNA - Found only during cell division - DNA is not being used for macromolecule synthesis ### Chromatin - Unwound DNA - Found throughout Interphase - DNA *is* being used for macromolecule synthesis Chromosomes, Eukaryote ====================== Alleles and Loci ----------------  A chromatid is a chromatid as long as it is held in association with a sister chromatid at the centromere When two sister chromatids separate (after metaphase) they go from being a single chromosome to being two different chromosomes Eukaryote Cell Cycle ====================   Mitotic Spindle ===============  Cytokinesis, Plants =================== Prophase -------- Metaphase ---------  Anaphase -------- Telophase --------- "Sisters" at opposite poles Nuclear envelope reformation. Reforms from endomembrane Chromosome decondensation Cytokinesis already under way Cytokinesis ----------- Meiosis I --------- Meiosis II ----------  Variation via the Sexual Cycle ------------------------------  Crossing Over: After crossing over and synapsis, sister chromatids are no longer identical  Independent Assortment: Each human can produce over 8.3 million different gametes by random shuffling of chromosomes in meiosis I  Fertilization: couple can produce over 64 trillion (8.3 million x 8.3 million) different zygotes during fertilization. This figure *does not* take into account diversity created by crossing over