Gene Action: Understanding Genetics through Examples, Study notes of Animal Biology

Download Gene Action: Understanding Genetics through Examples and more Study notes Animal Biology in PDF only on Docsity! Improvement Through Selection: Gene Action ANSC327 Spring 2009 Second Lecture (Siewerdt) Gene Action Examples (1) Behavior Happy Happy Sad Genotype HH Hh hh http://it.stlawu.edu http://i111.photobucket.com Gene Action Examples (2) Wool Production Genotype Yield BB 20 lb Bb 14 lb bb 8 lb http://www.ansi.okstate.edu/breeds/sheep/ Types of Gene Action Single locus • Additivity • Dominance – Complete dominance – Incomplete dominance – Overdominance – Underdominance Two or more loci • Epistasis Data required: • Genotypic information • Phenotypes for each genotype Special Cases • Sex-linked (X chrom.) • Holandric genes Genetics of Complex Traits • Polygenes – Many loci, each with a small effect – Phenotype: combination of polygenic effects • Individual Loci – Basis of polygenic expression – Each has own type of gene action • Quantitative Trait Locus (QTL) – Locus with large genetic effect – What is “large”? Suggestion: 1% of σ2P Terminology and Framework • Average of values of the two homozygotes • Effect of an allele is one-half the difference of values of the two homozygotes • Dominance deviation is the difference between the heterozygote and average • Examine value of dominance deviation, or compare effect to dominance deviation to determine gene action