Week 3, Lecture 3, Meiosis

Week 3, Lecture 3, Meiosis - 1 B I O L O G Y 0 2 3...

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Unformatted text preview: 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 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 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...
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This note was uploaded on 04/18/2010 for the course BIOLOGY 1223 taught by Professor Gardiner/lajoie during the Spring '09 term at UWO.

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Week 3, Lecture 3, Meiosis - 1 B I O L O G Y 0 2 3...

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