Ch 13 Cell Division-Meiosis

Ch 13 Cell Division-Meiosis - Cell Division: Meiosis...

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b b B B a a A A Cell Division: Meiosis Biology 1A Chapter 13 Q: What is the relationship among DNA, a gene, and a chromosome? A: A chromosome contains hundreds of genes, which are composed of DNA. Q: What is an example of a gene? A: A discrete DNA sequence that codes for a particular polypeptide. Sex is not the same as Reproduction Sex and reproduction are not the same thing o Sex is combining genetic material from two cells o Bacteria can reproduce without combining genetic material o Eukaryotic cells can divide asexually (mitosis) o Eukaryotic cells undergo meiosis in preparation for sex (in the biological sense!) o SEX increases genetic diversity! Ploidy Haploid cells have one copy of genetic info o Most bacterial cells are haploid o Germ cells in animals are haploid Diploid cells have two copies of genetic info Whaa? Sexual Life cycles include meiosis A life cycle is the generation pattern, or reproductive history of an organism Example: Humans (fig. 13.5) o Each individual is diploid and has 46 chromosomes, or 23 pairs o 22 of the pairs are autosomes, the last pair are sex chromosomes (the Y chromosome determines sex) o Gametes are haploid Q: How many haploid sets of chromosomes are present in an individual cell with a diploid chromosome number of 46? A: 2 Q: How many copies of a gene (say, alleles for the first enzyme of glycolysis), exist in a diploid cell? A: 2 Q: How many copies of a gene (say, alleles for the first enzyme of glycolysis), exist in a haploid cell? A: 1
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Sexual life cycles include meiosis, cont. In life cycles of other organisms, the diploid stage may not dominate (fig 13.6) o Haploid forms may be multicellular and able to live independently (fungi) Alternation of generations between multicellular haploid and diploid stages is present in plants In all cases, doubling and halving chromosome number leads to new genetic combinations In animals, Meiosis occurs during gamete formation o Gametes are the only haploid cells Plants and some algae Exhibit an alternation of generations The life cycle includes both diploid and haploid multicellular stages In most fungi and some protests Meiosis produces haploid cells that give rise to a
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This note was uploaded on 04/15/2008 for the course BIS 1A taught by Professor Gearhart during the Spring '07 term at UC Davis.

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Ch 13 Cell Division-Meiosis - Cell Division: Meiosis...

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