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Meiosis - BILD1 Lecture 13 Meiosis 5/13 2008 Mitosis and...

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BILD1 Lecture 13 Meiosis 5/13/ 2008
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Mitosis and Meiosis Similar strategies with totally different functions Strategies : Chromosome duplication and separation Functions : Somatic cell division (mitosis) Gametes production (meiosis)
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Asexual vs. Sexual Reproduction Asexual reproduction One parent produces genetically identical offspring by mitosis. Clones. Parent Bud 0.5 mm Sexual reproduction Two parents give rise to offspring with unique combinations of genes. Important for genetic diversity.
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Offspring inherit a combination of parental traits Heredity transmission of traits from one generation to the next Variation offspring differ from parents and siblings Genetics scientific study of heredity and hereditary variation The process of meiosis underlies the genetic basis of heredity and hereditary variation
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Genes - units of heredity - segments of DNA Offspring acquire genes inherited on chromosomes Chromosomes Diploid : one set inherited from mother, one set from father Humans = 2 sets of 23 chromosomes (46 total) The process of meiosis ensures the inheritance of a combination of chromosomes (…traits…) from mother & father
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Fertilization Fusion of sperm & egg gametes to generate zygote with two sets of chromosomes Meiosis “Reducing Division” (in half) Division of diploid cell with two sets of chromosomes to generate 4 haploid gametes, each with one set of chromosomes Meiosis and Fertilization alternate in sexual life cycles
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HAPLOID DIPLOID HAPLOID Key Haploid ( n ) Diploid (2 n ) Haploid gametes ( n = 23) Ovum ( n ) Sperm Cell (n) MEIOSIS FERTILIZATION Ovary Testis Diploid zygote (2 n = 46) Mitosis and development Multicellular diploid adults (2 n = 46) Meiosis reduces & fertilization restores chromosome count during sexual life cycle Fertilization Meiosis
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Gametes Diploid multicellular organism MEIOSIS FERTILIZATION n n n 2n 2n Zygote Mitosis Types of Sexual Life Cycles differ in the timing of meiosis and fertilization ANIMALS -meiosis in gamete formation -only gametes are haploid PLANTS & ALGAE - “Alternation of generations” -Both diploid and haploid multicellular stages MEIOSIS FERTILIZATION n n n n n 2n 2n Haploid multicellular organism (gametophyte) Mitosis Mitosis Spores Gametes Mitosis Zygote Diploid multicellular organism (sporophyte)
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One set of chromosomes inherited from each parent Humans Karyotype (2n = 46) 2 sets of 23 chromosomes, including 2 sex chromosomes 5 µ m Pair of homologous chromosomes Sister chromatids Diploid cells have two sets of chromosomes Homologous chromosomes - Two chromosomes composing a pair - Have the same characteristics Sex chromosomes - Distinct from each other (X and Y) - Determine sex: XX female, XY male
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Diploid cell has two sets of chromosomes Maternal set of chromosomes ( n = 3) Paternal set of chromosomes ( n = 3) 2 n = 6 Two sister chromatids Two nonsister chromatids in a homologous pair
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