lecture 13 - 8/26 Meiosis Is the basis of sexual...

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8/26 Meiosis Is the basis of sexual reproduction Is the production of gametes The chromosomal number doubles Key Concepts 1. Heredity is the transmission of traits from one generation to the next 2. Clone- a group of genetically identical individuals produced by asexual reproduction 3. The fusion of gametes called fertilization or syngame 4. Meiosis is the basis of sexual reproduction 5. Sexual reproduction dominates the life cycle of nearly all animals a. Many different variations that increases the offspring survival 6. Crossing over, random segregation, and random fertilization contributes to variation in traits among offspring a. Affects what you are immune to or not for diseases Heredity: Asexual Reproduction o Is from cloning or mitosis only o Example sponge or jellyfish, earthworm, hydra Sexual reproduction o Example: humans, insects, mammals, reptiles The roles of meiosis in life cycle Sperm (long tail and smaller in size) fertilizes the egg Sperm fertilizes the egg producing a zygote (2n = 2 sets of chromosomes, one from mom n 1 from dad), then mitosis occurs producing identical daughter cells, babies and then adults then making more gametes (meiosis) Occurs in the ovaries and testis Production of gametes Process of Meiosis DNA replication occurs in interphase prior to meiosis Meiosis !: o Interphase: no chromosomes can be seen, o Prophase: 90%, chromosomes condense and visible, homologous chromosomes ( synapsis) to form tetrads ( mother and father) Crossing over (chiasmata) occurs between one of mother and one of fathers chromosomes, can happen at multiple sites (double crossing over) o Metaphase: chromosomes line up in the middle randomly , o Anaphase: Random segregation/independent assortment, homologous separate (tetrad), sister chromatids remain together (X shape), not pure
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chromosomes , each daughter cell has equal chance to get any chromosomes, chromosome 1 goes to one cell and other goes to other o Telophase: chromosomes remain condensed and cleavage furrow NO DNA replication between meiosis I and meiosis II Meiosis II is similar to mitosis o Sister chromatids separate o Daughter cells are NOT identical to parental cells o Haploid chromosome number = 4 daughter cells o Daughter cells are NOT identical to each other After chromosome duplication the similar sister chromatids join to form a tetrad. o
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This note was uploaded on 10/20/2011 for the course BIO 311 D taught by Professor Zhao during the Fall '08 term at University of Texas at Austin.

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lecture 13 - 8/26 Meiosis Is the basis of sexual...

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