Chapter 4 Genetics, Evolution & Plasticity.docx - Module...

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Module 4.1: Genetics & Evolution of Behaviour Genes:units of heredity that maintain their structural identity from one generation to another-Genes come in pairs because they are aligned along chromosomes(strands of genes)-A gene is composed of DNAoStrand of DNA serves as a template for synthesis of RNAoDNA contains 4 bases (adenine, guanine, cytosine & thymine) order of these bases along RNA molecule determine which protein must the amino acid add -Homozygous: identical pair of genes on the 2 chromosomes-Heterozygous: unmatched pair of genes e.g. you have a gene for blue eyes & brown eyes-Genes can be dominant, recessive or intermediateoDominantgene shows strong effect in either homozygous or heterozygous conditionoRecessivegene only shows its effect in a homozygous conditionE.g. a gene for brown eyes is dominant and a gene for blue eyes is recessive if you have 1 gene for brown eyes & 1 gene for blue THEN the result will be brown eyes A child has a 25 % chance of being homozygous of dominant gene (TT), 25% chance of being homozygous forrecessive gene (tt) & a 50% chance ofbeing heterozygous (Tt)Sex Linked & Limited Genes The genes on the sex chromosomes (X & Y) are sex linked genesoXX FemaleoXY MaleAll other chromosomes except for X & Y in the body are autosomal genesSex limited genesare genes that exert their effect primarily in one sexbecause of activation by androgens or estrogens although members of both sexes may have the geneoPresent in autosomal chromosomes Mutationheritable change in DNA moleculeType of mutation is replication/duplication of a chromosome (tiny part of chromosome appearing twice or getting deleted)oCan be an explanation for brain-relevant genes for schizophrenia Epigeneticsdeals with changes in gene expression without modification of DNA sequenceVarious experiences can turn a gene on or offoE.g. if a mother rat is malnourished during pregnancy, her offspring alter the expression of certain genes to conserve energy & adjust to a limited food sceneoRat pups with low degree of maternal care alter the expression of certain genes in hippocampus leading to high vulnerability in stressful situations
Epigenetic changes are critical; when you learn something your brain stores the information by increasing activity in certain genes while decreasing othersHow can an experience modify gene expression?-Histonesare proteins that bind DNA into its helical structure oTo activate a gene, the DNA must partially unwind oThe result of an experience (e.g. maternal deprivation, cocaine exposure) alters chemical environment in a cell In some cases, the outcome adds acetyl groups to the histone tails near a gene causing histones to loosen their grip on DNA & turns the gene offoAdding methyl groups also promote genes to turn offE.g. severe traumatic experience decreases methylation of brain genes increasing risk of depression, PTSDHeredity & Environment High heritability

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