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Reproduction & Genetics
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Asexual Reproduction Reproduction requiring one parent & leading to genetically identical offspring Bacteria reproduce ‘asexually’… dividing by mitosis doubles the population If mitosis were only strategy for reproduction, we would produce exact clones (What would be the risk of having exact genetic copies of ourselves running around?)
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Asexual Reproduction cont’d…
Asexual reproduction also requires less energy, and allows organisms to be more flexible in adverse environmental conditions, which can perpetuate the species as a whole.
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Sexual Reproduction Vocabulary
Match the following definitions to the terms… Gamete Zygote Fertilization A cell formed by fusion of two gametes Joining of male and female gametes A male or female reproductive cell
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Sexual Reproduction Vocabulary…
Haploid Diploid Meiosis Cell that contains pairs of homologous chromosomes Process producing cells containing half the number of chromosomes as the parent cell Cell that contains half the number of chromosomes as the parent cell
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Sexual Reproduction Requires two parents
Produces genetically unique offspring Male gamete fuses with female gamete A zygote is formed gamete = haploid (n) zygote = diploid (2n) What is the human haploid number? diploid number?
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Human Life Cycle
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Benefits of Sexual Reproduction
In groups of 2-4 Take 10 minutes to research the benefits of sexual reproduction (vs. asexual reproduction) Write your findings on chart paper to share with the class “Why is sexual better than asexual?”
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Meiosis (MY-OH-SIS) The process that produces gametes with a haploid number of chromosomes. Two key outcomes of meiosis: Genetic Reduction Genetic Recombination
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Why meiosis? If we reproduced only via mitosis… all cells would have 2n chromosomes. If we added a sperm cell (2n) with an egg cell (2n) we would end up with a 4n zygote! Additional chromosomes result in cell death or severe abnormalities. Other benefits of meiosis?
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Interphase Cells dividing by meiosis will proceed through the G1, S, and G2 phases before dividing. This includes replication of chromosomes, taking place during the ____ phase. At the start of meiosis, the cell contains duplicated chromosomes.
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Phases of Meiosis Like mitosis, the events in meiosis can be grouped into four distinct phases: ______, ________, __________, and _________. Meiosis however, involves two complete cycles of the four phases. These two cycles are known as Meiosis I and Meiosis II.
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Meiosis I Prophase I Pairs of homologous chromosomes line up side by side This is called ‘synapsis’: aligning of homologous chromosomes during Meiosis I & II Segments of chromosomes may be exchanged Centrosomes move to poles, spindle apparatus forms
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Metaphase I
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Anaphase I
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Result is two haploid daughter cells.
Telophase Result is two haploid daughter cells.
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Meiosis II Phases of meiosis II are very similar to the phases of mitosis Key difference: Cell undergoing meiosis II is haploid Cell undergoing mitosis is diploid
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Meiosis II cont’d… During metaphase II, single chromosomes line up along the equator II I
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Meiosis II cont’d… During anaphase II, sister chromatids are pulled apart at the centromere II I
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