Transcript Unit 5
Unit 5: Cell Growth and Reproduction Unit 5: Cell Growth and Reproduction • The events that occur during the cell cycle – Interphase: The longest‐lasting phase of the cell cycle in which a cell performs the majority of its functions, such as preparing for nuclear division and cytokinesis. Unit 5: Cell Growth and Reproduction • Nuclear division – Mitosis: A nuclear division resulting in the production of two somatic cells having the same genetic complement as the original cell. • Prophase: nucleus disappears, chromosomes pack together. • Metaphase: chromosomes line up in the center of the cell. • Anaphase: sister chromatids separate and move to opposite sides. • Telophase: chromosomes uncoil, both nuclei reform. Unit 5: Cell Growth and Reproduction • Nuclear division – Meiosis: A two‐phase nuclear division that results in the eventual production of gametes with half the normal number of chromosomes. • Meiosis I: homologous chromosomes separate. – Prophase I: chromosomes pack tightly. Homologous chromosomes pair up. Crossing over can occur. – Anaphase I: homologous chromosomes separate and move to opposite sides. • Meiosis II: sister chromatids separate. There is no DNA replication. Unit 5: Cell Growth and Reproduction • Nuclear division – Cytokinesis: The final phase of a cell cycle resulting in the division of the cytoplasm. Unit 5: Cell Growth and Reproduction • Compare the processes and outcomes of mitotic and meiotic nuclear divisions – Mitosis is used to repair cells, used in asexual reproduction, and used in growth. Meiosis is only used for sexual reproduction. – Mitosis produces genetically identical daughter cells. Meiosis produces four different daughter cells with half the number of chromosomes. Meiosis is only used to form gametes. – How chromosome separation is different: the sister chromatids do not separate in mitosis only the homologous chromosomes. In meiosis I the homologous chromosomes separate. In meiosis II then the sister chromatids. – When the similar chromosomes line up early in meiosis, they may swap portions. This is “crossing over” and makes the product of meiosis (and sex) more varied and unpredictable. Unit 5: Cell Growth and Reproduction – Nondisjunction: The process in which sister chromatids fail to separate during and after mitosis or meiosis. • If chromosomes or parts of chromosomes do not separate correctly during any form of cell division, the cells produced may have too much or too little genetic information. • If an egg or sperm has too many or too few chromosomes, the entire organism formed from it will usually not develop. Down syndrome (with an extra 21st chromosome) is one of very few survivable situations. Unit 5: Cell Growth and Reproduction • How DNA replication results in transmission and/or conservation of genetic information – DNA replication: The process in which DNA makes a duplicate copy of itself. • Every time the cell divides, DNA must replicate. DNA copies have to be accurate. – Original strand of DNA used as a template. DNA is built from 2 complementary strands. Every time more DNA is copied, one of the “old” strands becomes complement to the new. This maintains the correct order of the code (usually). – Base pairing rules: adenine with thymine. Cytosine with guanine. Video Review • Mitosis Animation • Mitosis Song Video Review • Meiosis Animation • Meiosis Song Video Review • Mitosis vs. Meiosis Video Review • Nondisjunction Video Review • DNA Replication song • DNA Replication Animation