ext_mendel - Extensions to Mendelism Mendel's pea...

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Extensions to Mendelism Mendel's pea experiments used a very simple genetic system: each gene had 2 alleles, one dominant and one recessive, and genes did not interact with each other. We are going to look at some variations: different forms of dominance, multiple alleles, interactions between genes, and environmental effects.
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Partial (Incomplete) Dominance Mendel studied complete dominance : the heterozygote looks exactly like the dominant homozygote. In partial dominance , the heterozygote has phenotype intermediate between the two homozygotes. Example: Four o'clock plants. Red flowers x white flowers gives pink F1's. Pink is intermediate between red and white. Selfing the F1's gives 1/4 red (RR), 1/2 pink (Rr), and 1/4 white (rr)
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Co-dominance In co-dominance, both parental alleles are expressed in the heterozygote. Example: blood groups. Antigens on the surface of red blood cells cause them to clot in the presence of the corresponding antibody. The MN blood group antigens are coded for by the L gene: the 2 alleles are called L M and L N . A L M L M homozygote has the M blood type: blood clots in the presence of anti-M antiserum, but not in the presence of anti-N serum. Similarly, a L N L N homozygote has the N blood type: blood clots in the presence of anti-N antiserum, but not in the presence of anti-M serum. The L M L N heterozygote has the MN blood type: it clots with both anti-M and anti-N antiserum. These red blood cells have both antigens on their surface. Thus, the MN blood group alleles are co- dominant.
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Electrophoresis When an organism's DNA or proteins are examined closely, almost all genes are co-dominant. Both alleles of the gene are present, even if they don't contribute equally to the phenotype. Electrophoresis is a way of separating the DNA of the genes or the proteins the genes produce. Electrophoresis depends on a fundamental physical property: charged objects move in an electric field. DNA and RNA have one negative charge per nucleotide. Most proteins also have a net negative charge, caused by 2 of the 20 amino acids, which have a negative charge. Since opposite charges attract, most nucleic acids and proteins move towards the positive pole. The speed the molecules move is proportional to their charge and inversely proportional to their size: small, highly charged molecules move faster than large, less charged molecules. Electrophoresis is done in a gel matrix, to prevent diffusion from confusing the results.
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More Electrophoresis As an example, the enzyme "phosphatase" removes phosphate groups from other molecules. When an extract is made of the proteins in an organism, it is possible to separate the proteins by electrophoresis and then stain the gel so only the phosphatase will
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ext_mendel - Extensions to Mendelism Mendel's pea...

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