205_14_Mendel_post

205_14_Mendel_post - Chapter 14 Mendel and the Gene Gregor Johann Mendel 1822-1884 Austrian Augustinian monk Always wanted to be a high school

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Gregor Johann Mendel, 1822-1884 Austrian Augustinian monk. Always wanted to be a high school science teacher  but had terrible test anxiety (flunked teachers' test  2x!) So instead he started breeding  pea plants (Pisum sativum)  at his monastery.     Chapter 14: Mendel and the Gene
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Some terms: Character  = Heritable feature, like flower color   Trait  = variant of character, like purple vs. white
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Mendel's first great discovery: not all purple flowers are the same underneath Purple Purple Purple White What they look like These ALWAYS pass PURPLE  genes to their offspring But these ones have some  purple -flowered offspring  and  some  WHITE -flowered  offspring! (when bred to white mate) These ALWAYS have white-flowered offspring (when bred to white mate) How they breed
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Now we know: some genes are present but "hidden" PHENOTYPE Purple Purple Purple White GENOTYPE AA ( homozygous ) Aa ( heterozygous ) Aa ( heterozygous ) aa ( homozygous )
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Alleles = alternative versions of a gene Allele for purple flowers Flower-color gene Homologous pair of chromosomes Allele for white flowers Phenotype :  physical, biochemical, or physiological trait. Roughly: "What it looks like"  Genotype :  genetic make-up (i.e. which alleles an organism actually has,  regardless of what it looks like on the surface) Locus = physical location of a gene (e.g. on long arm of chromosome #13)
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Which trait is recessive? Which trait is dominant? Usually one allele is DOMINANT P Generation (true-breeding     parents) Purple flowers White flowers × F 1 Generation ("first filial" generation = offspring) All plants had purple flowers Recessive - the allele is masked by presence of the other allele. Dominant - the allele is always "visible" in the phenotype.
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Peas: Purple is dominant to white P Generation (true-breeding     parents) AA aa × F 1 Generation (hybrids) Aa Dominant allele designated w/UPPERCASE letter Recessive w/lowercase This does not mean purple is "better" than white Does not mean evolution will favor purple, either. (white might be better) ALL it means is F1 plants have purple flowers.
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The recessive trait reappears! (This was already known.) Mendel's discovery: It's not random! It's a 3:1 ratio! (if  you have enough  pea plants) Continuing the experiment for another generation: P Generation (true-breeding     parents) Purple flowers White flowers × F 1 Generation (hybrids) Cross these plants. .. 2
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Look at the RATIOS in these "F2" plants: 3 1 1 2 1 Purple Purple Purple White What they look like These ALWAYS breed  purple-flowered offspring But these ones have some purple- flowered offspring and  some  WHITE -flowered offspring! (when bred to white mate)
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This note was uploaded on 04/08/2008 for the course BIO 205 taught by Professor Stevens during the Spring '08 term at Portland.

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205_14_Mendel_post - Chapter 14 Mendel and the Gene Gregor Johann Mendel 1822-1884 Austrian Augustinian monk Always wanted to be a high school

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