Lecture4_1-20-10

Lecture4_1-20-10 - Extensions to Mendelian Genetics 1. 2....

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Extensions to Mendelian Genetics 1. Mutation classification 2. Incomplete dominance 3. Codominance 4. Multiple alleles 5. Recessive epistasis 6. Dominant epistasis 7. Recessive lethality 8. Gene interactions in different pathways 9. Complementary gene interaction 10. Pleiotropy 11. Sex influenced traits
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Alleles 1) Alternative forms of a gene are called alleles. 2) Mutation is the source of alleles. 3) The wild-type allele is the one that occurs most frequently in nature and is usually, but not always, dominant.
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Classification of alleles 1) Loss-of-function mutation ( hypomorph ): a mutation causes the reduction or loss of the specific wild-type function. 2) If the loss is complete, the mutation has resulted in what is called a null allele. 3) Gain-of-function mutation ( hypermorph ): a mutation causes an increase of the normal function.
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Allele series (Example: Drosophila white gene) Wild type white, null white, hypomorph 1 white, hypomorph 2 white, hypomorph 3
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Genetic definition of a null m m Null, if m del = m m Hypomorph, if m del < By definition, a deletion that removes the gene entirely is a null. In addition, a mutation is considered a null if the phenotype of the homozygous mutant is identical to those of the mutation over a deletion. A mutation is considered a hypomorph if the phenotype of the homozygous mutant is less severe than those of the mutation over a deletion.
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Dominant-active: refers to those alleles, when heterozygous, produce gain-of-function-like phenotype. Dominant-negative: refers to those alleles, when heterozygous, produce loss-of-function- like phenotype. Haplo-insufficient: refers to those loss-of- function mutations, when heterozygous, produce phenotype (therefore, dominant). Note that dominant or recessive do not indicate
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This note was uploaded on 02/09/2010 for the course BIOL 241 taught by Professor Henrychang during the Spring '10 term at Purdue University.

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Lecture4_1-20-10 - Extensions to Mendelian Genetics 1. 2....

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