Lecture_15_DulaiS09_Meiosis_DULAI

Lecture_15_DulaiS09_Meiosis_DULAI - Lecture 13 Agenda:...

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Lecture 13 Agenda: Meiosis – Sexual reproduction & the generation of genetic variation 2. What are the two major steps of meiosis? What occurs in each? What does each accomplish? 1. What is meiosis? Where does it take place? What is the “goal” of meiosis? What is its relationship to sexual reproduction? 3. In what three ways does sexual reproduction create the genetic variation (genetic diversity)? What steps in meiosis contribute to this? What is the third mechanism by which genetically unique individuals are created?
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What is asexual reproduction? • Products of mitosis - 2 daughter cells - are genetically identical to each other and to the parent cell from which originated = clones. • In unicellular eukaryotes & some multicellular eukaryotes mitosis accomplishes asexual reproduction. ¾ What mitosis does NOT do is generate any genetic variation (diversity) because parent and offspring are genetically identical. • Any form of reproduction in which offspring arise from only 1 parent and are genetically identical to that parent
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Why is genetic variation so important? • Fundamental form of diversity on which natural selection acts to give rise to Earth’s great biodiversity – past, present and future!! • Sexual reproduction · Process by which genetically unique reproductive cells are formed What mechanism do eukaryotic organisms have for generating genetic variation, i.e. producing offspring that differ genetically from their parents? · combined via fertilization ·t o f o r m a n e w genetically uniquecell · which grows and develops into a genetically uniqueadult that produces reproductive cells
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How do organisms that engage in sexual reproduction keep the number of chromosomes stable from generation to generation? • If specialized reproductive cells were diploid (2n), fertilization would result in a 4n cell. · Number of sets of chromosomes would increase with each fertilization event infinitely! + ? 2n Egg 2n Sperm • Know this is not the case generally, because each species has a stable, characteristic number of chromosomes! • So what maintains number of chromsomes from generation to generation? =4n Fertilized egg = zygote
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What is meiosis? Type of nuclear division that is occurs exclusively for the purposes of sexual reproduction · Meiosis initiates process that leads to formation of haploid (n) reproductive cells = gametes Figure 10.8 · Fertilization restores diploid (2n) condition as the haploid nuclei (n) of two gametes fuse · Unlike mitosis which occurs in all eukaryotes, meiosis only occurs in eukaryotes that reproduce sexually (this means some unicellular & all multicellular- including plants, animals, fungi)
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Where does meiosis take place in the body of animals ?
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This note was uploaded on 11/18/2010 for the course SS 101 taught by Professor Denver during the Spring '10 term at Alabama.

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Lecture_15_DulaiS09_Meiosis_DULAI - Lecture 13 Agenda:...

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