BIEB 166 Lecture 6 (WI13)

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Biol/Ecology, Behavior, & Evol
BIEB 166
James Nieh

Lecture 6 Definitions Gene - A unit of heredity; - More specifically, a stretch of DNA that codes for a single protein; - We often think of a gene as encoding the expression of a single trait, such as eye color; - In fact, one gene may greatly influence an individual's eye color, but most genes influence more than one trait. Locus - A specific location on a chromosome; roughly synonymous with gene. Allele - One of two or more variants of a gene, which typically code for slightly different proteins which in turn yield different forms of the trait(s) in question. Genotype - A description of the alleles present at one or more loci of a given individual. Phenotype - The observable characters of an individual; a consequence of both genotype and environment. Polygenic Inheritance - Inheritance of continuously variable traits influenced by mulitple loci Innate/Learning Toad 1. Innate - Sticks out its tongue and eat 2. Learning - Eats a bumblebee ○ Stinging its mouth - The next time a toad sees a bumblebee, it refuses to eat the bee - No longer initiate the FAP even visually stimulated by the bee - Even an innate behavior can be modified by learning A Continuum of Behavioral Programs (Ernst Mayr) Two types 1. Closed: developmentally fixed - No further learning can alter the behavior - Innate - Eg. Birds decide who to mate with/who their parent is 2. Open: developmentally flexible - Learn at any point in the animal's life - Learning - Most animal fall between open and closed Methods 1. Hybridization 2. Quantitative genetics (twin studies, artificial selection) 3. QTL analysis 4. Molecular genetics (knock out studies) 5. Behavioral genomics Hybridizations Studies Lovebirds, species of Agapornis (William Dilger) - Readily buy them in pet store, easily hybridized 1. Peach-faced - Tucks the nest material in the tail, carry them to the nest - Leaves the beak free - Have to be a good tucker - Have to be a good tucker - Tucking behavior is largely innate 2. Fisher's - Carry the nest-building material in the beak 3. Peach-faced x Fischer's - If the behavior is controlled by genetics, the behavior should be in the middle of the both behaviors - Hybrids: 6% Carry and 94% Tuck ○ Example of dominant trait, tucking is dominant ○ Hybrids cannot tuck properly: they would lose their nest material ○ Experience leads to modified behavior  Small increase in % that carry after several months, majority still try to unsuccessfully tuck and do so even three years later - Largely closed behavior Crickets (discussed before) - Study of maternal effect ○ Male offspring sound more like the mom Quantitative Genetics - Study of continuously varying traits Twin studies - Heritability ○ Proportion of variation in a phenotypic character in a population due to individual genetic differences that will be inherited by the offspring ○ There is random assortment of the gene, chromosomes cross with each other (so may not be inherited) 1. Monozygotic twins - Identical twins - One egg, one sperm (one fertilization) 2. Dizygotic twins two fertilizations - Two separate eggs, sperms - Fraternal twins 3. Compare similarity of twin types - Monozygotic has greater similar - Additional similarity within monozygotics should be due to greater genetic similarity - How the genes arranged controls a lot of the phenotype - Control for environment by rearing apart - Suggests a genetic basis for many traits 4. Problems with methods - Human twin studies cannot be as rigorously controlled as animal studies ○ Rearing environments ay contribute to similarities - Behaviors are typically controlled by multiple genes ○ Interactions between alleles play an important role in expression of traits ○ Recombination of alleles are different between fraternal twins, but not identical twins - Similarity in identical twins phenotypes = affect of genes + combination of specific alleles - Recombination among alleles in sexual reproduction is random, it is not inherited - Therefore comparisons between identical and fraternal twins can overestimate heritability ○ They have identical arrangement of alleles - Phenotype of identical twi
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