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Week 3, Lecture 3, Meiosis

Week 3, Lecture 3, Meiosis - Meiosis BIOLOGY 023 19-Sep-09...

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1 B I O L O G Y 0 2 3 19-Sep-09 Gardiner 1 Meiosis B I O L O G Y 0 2 3 19-Sep-09 Gardiner 2 Haploid Haploid = 1n = cells with one complete set of chromosomes Unfertilized egg cells are haploid Sperm cells are haploid Haploid sperm fuses with haploid egg to get diploid zygote (fertilized egg) Male parent provides 23 chromosomes (1 set) and female parent 23 chromosomes (1 set) B I O L O G Y 0 2 3 19-Sep-09 Gardiner 3 Diploid Diploid = 2n = cells with two complete sets of chromosomes Almost all body cells of human are diploid – eg: muscle, brain, bone, skin cells….. Diploid human cells have 46 chromosomes Diploid cells DO have pairs of homologous chromosomes B I O L O G Y 0 2 3 19-Sep-09 Gardiner 5 Sexual vs. Asexual Reproduction Asexual Reproduction Individual inherits all its genes from one parent Offspring are genetically identical to parent 1. One celled organisms divide 2. Hydra budding 3. Self pollinating flowers (dandelions) 4. Some lizards 5. Aphids 6. Aspens shoot up from roots -genetic variation comes only from mutations -greatly reduced ability to evolve 3 mm 7 cm 1.5 mm 4 µm
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2 B I O L O G Y 0 2 3 19-Sep-09 Gardiner 7 Sexual vs. Asexual Reproduction Sexual Reproduction – Each new individual gets ½ genetic information from one parent & ½ from other parent – Offspring are genetically different from both parents – Sexual reproduction produces much greater variation Evolution requires pre-existing genetic variation Sexual reproduction provides much of the pre-existing variation B I O L O G Y 0 2 3 19-Sep-09 Gardiner 8 Life Cycles A diagrammatic representation of the events in the organisms development and reproduction Pay attention to ploidy level and where in life cycle meiosis occurs Animal life cycles have a dominant diploid phase Most cells in our bodies are diploid, germ line diploid cells will undergo meiosis to produce gametes B I O L O G Y 0 2 3 19-Sep-09 Gardiner 9 Life Cycles Plant life cycles have two sequential phases that are termed alternation of generations Many protists and fungi have a haploid dominated life cycle Many protists reproduce by mitosis until their environment deteriorates, then undergo sexual reproduction to produce a resting zygotic cyst 19-Sep-09 Gardiner 10 Fig. 10.9 B I O L O G Y 0 2 3 19-Sep-09 Gardiner 11 Sexual Cycle (humans) Somatic cells = body cells 46 chromosomes in human body cells All 46 chromosomes are not alike 23 types of chromosomes 2 or each type ( 2 x 23 = 46) – Get one of each type from father – Get one of each type from mother Fig. 10-7d, p. 207
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3 Sexual Cycle (humans) Somatic cells have 23 pairs of chromosomes – Homologous chromosomes = two chromosomes of a given matched pair – Each chromosome has many genes – Each gene occupies a specific “locus” on a specific chromosome Remember chromosomes are long linear strands of DNA – Homologous chromosomes have homologous genes at homologous loci ( but the two genes at the
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