Lecture9-reading.pdf - • 9.3 Genetic Recombination In Eukaryotes Meiosis 1 1 1 1 1 Sexual reproduction is producing offspring when male and female

Lecture9-reading.pdf - • 9.3 Genetic Recombination In...

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9.3 - Genetic Recombination In Eukaryotes: Meiosis 1 Sexual reproduction is producing offspring when male and female gametes come together (sperm cells and eggs cells in animals) 1 Meiosis produces cells with half the number of chromosomes than the somatic (body) cells 1 Fertilization brings the gametes together making a zygote in which the normal amount of chromosomes in a species is restored 1 If the halving of chromosomes didn’t happen the number of chromosomes in a species would double after each generation 1 Meiosis and fertilization mix the DNA into different combinations ensuring that the offspring will be different than their parents and their siblings( this produces the variability that it then acted on by natural selection) 9.3a - Meiosis Occurs in Different Places In Different Organismal Life Cycles 1 Not all living organisms will make gametes by meiosis, various plants and some fungi will produce haploid cells which are spores, these spores will then do mitosis to form other multicellular bodies which then make gametes Animals (figure 9.9a) 1 Diploid phase is the majority of the life cycle 1 Meiosis produces gametes in the short haploid phase 1 Males produce 4 functional sperms cells 1 Only 1 of the 4 cells that female produce becomes functional as an egg 1 Fertilization restores the diploid phase (animals are only haploid while gametes) 1 Note that there are no mitotic divisions during the haploid phase Most Plants and Some Fungi (figure 9.9b)
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1 Mitotic divisions happen in both the diploid and haploid phase 1 Fertilization produces a zygote which then goes under mitosis and the result is a sporophytes 1 After the sprophytes become mature (by mitosis) they produce haploid cells by meiosis called spores 1 Spores are not gametes! They grow by mitosis becoming a haploid and multicellular individuals called gametophytes 1 When mature, the cells of the gametophytes may turn into egg or sperm cells 1 Note that all the egg or sperm cells are gentically indentical because gametophytes will go under mitosis, meiosis doesn’t happen in gametophytes 1 The sperm and egg cells will produce a zygote which will then divide by mitosis to produce the sporophyte again 1 In all plants the female gametophyte remains in the plant while the male gametophyte is released as pollen and when
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