Chapter 5

Chapter 5 - Dhruv Patel Chapter 5: Extensions and...

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Dhruv Patel Chapter 5: Extensions and modifications of basic principles 1. Mutant Vs. Wild type a. The wild type has the normal phenotype In nature i. Can be either dominate or recessive b. Mutant has a phenotype different than the wild type c. If the mutant allele is recessive the allele symbol begins with a lowercase letter and vice versa d. The same symbol is used for both wildtype and mutant alleles except the wildype has a superscript: + 2. Dominance a. Determined by the phenotype seen in a heterozygote b. 3 forms i. Complete Dominance ii. Incomplete Dominance iii. Codominance Dominance 3. Complete Dominance a. When one allele is completely dominant over another 4. Incomplete Dominance a. A situation where the heterozygote is an intermediate in phenotype of both of the alleles b. EX: Snapdragons i. 2 allele for flower color: red and white ii. If a homozygous red is crossed with a homozygous white the result is a pink flower iii. If the pink flowers are crossed a 1:2:1 phenotypic ratio is observed
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c. EX: Taysachs Disease
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i. If looked at the health of an individual the disease appears to show complete dominance, but if locked at enzyme activity the disease shows incomplete dominance
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5. Codominance a. Occurs when each allele produces a distinct, detectable gene product and the heterozygote expresses both equally b. EX: MN Blood group antigens i. 2 alleles for blood group antigen LM and LN ii. 3 phenotypic possibilities Genotype Blood group L M L M M L M L N MN L N L N N c. EX: Sickle- Cell anemia i. Different from Tay sachs because heterozygotes make 2 products not one. 6.
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Chapter 5 - Dhruv Patel Chapter 5: Extensions and...

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