Chapter 14 Overview Complementation test
Dobbs, Gary, Meteorologist has reference to this Academic Journal, PHwiki organized this Journal Chapter 14 16 in addition to 18 March, 2004 From Gene to Phenotype Dominance, epistasis, gene interaction Overview Genetic in addition to environmental contributions interact to determine phenotype. Mutations in same gene usually result in mutant phenotype when present together. Mutations in different genes complement. Dominance comes in several types. Most characters are determined by sets of genes that interact with the environment. Modified genetic ratios reveal gene interactions, including epistasis.
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Complementation test Diagnostic test as long as allelism Mutants are crossed to bring two recessive mutations together in heterozygous as long as m if phenotype is mutant, mutations are in same gene they fail to complement both have loss of function if phenotype is wild-type, mutations are in different gene each mutant contributes normal gene at different locus complementation due to interaction of different proteins Heterokaryons used in haploid organisms
Interactions between alleles Dominant versus recessive Incomplete dominance intermediate phenotype 1:2:1 F2 ratio quantitative differences in gene dose Codominance equal presence of two gene products ABO blood groups sickle-cell hemoglobin HbA dominant as long as lack of anemia HbA in addition to HbB codominant as long as hemoglobin Alleles of a single gene can show various degrees of dominance. Dominance is determined by type of molecular interaction in addition to level of analysis.
Lethal alleles Cause death of organisms Recessive lethals masked in heterozygotes by wild-type allele Example: yellow coat color in mice AY is dominant as long as color AY is recessive lethal AY/A AY/A 25% AY/AY lethal 50% AY/A yellow 25% A/A wild-type Example of pleiotropism: gene affects multiple characters Lethal mutation Change in DNA sequence resulting in change in amino acid sequence Genetic load: total of deleterious in addition to lethal genes in population Often result of lack of activity or abnormal activity of encoded protein Lethality affected by genetic in addition to physical environment Detected by abnormal genetic ratios
Epistasis Allele of one gene eliminates expression of alleles of another gene, substituting its own phenotype Usually indicative of biochemical or developmental pathway (sequential gene activity) Involves genes at two or more loci Results in dihybrid F2 ratios that deviate from 9:3:3:1 B- Black bb Brown E- Deposition ee No deposition in hairs
Two pathways – black, orange Suppression Interaction between two molecules Product of one allele of a gene interferes with product of another gene on a different pathway Numerous causes nonsense suppressors mutant tRNA that reads premature stop codon protein-protein interactions
Coat color in mammals Five major genes, A, B, C, D, in addition to S A: affects distribution of pigment in hair A: agouti, yellow b in addition to on dark shaft a: nonagouti, no yellow; solid pigment B: determines color of melanin B = black b = brown C: permits color; c: no color D: full intensity; d: dilute color (uneven) S: no spots; s: spots (piebald)
Penetrance in addition to expressivity Penetrance percent individuals with a given allele that show the phenotype of the allele <100% penetrance a result of modifiers, epistasis, suppressors, environmental conditions Expressivity extent to which allele is expressed at phenotypic level affected by genetic background in addition to environment These phenomena make pedigree analysis in addition to genetic counseling more difficult
Assignment: Concept map, Solved Problems1 in addition to 2, All Basic in addition to Challenging Problems. Problems are particularly important as long as this chapter.
Dobbs, Gary Meteorologist
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