Test 2 Notes Power Point 5 Road Map A Primer on Molecular Genetics What do genes do How do they effect behavior How are genes inherited What are genetic polymorphisms How does neurotransmission relate to genes To behavior Introduction Molecular Genetics Behavioral Genetic Research answers the question How much do genes matter in the formation of the phenotype Molecular Genetic Research answers the question What specific genes matter A Primer on Genetics Deoxyribonucleic Acid DNA Chemical code in cell nuclei that allows us to develop and function Implicated in physical and non physical features Ex Physical Features Hair eye color Ex Non physical Features Impulsivity personality Consists of two genetic fibers called polynucleotides A Primer on Genetics Polynucleotides consist of four bases Adenine A Thymine T Guanine G Cytosine C 4 bases that make up DNA Bases on one Poly bond with the bases on the other A bonds with T G bonds with C Base Pairs A Primer on Genetics When base pairs work together to carry out a particular function in the body they are known as a gene About 20 000 25 000 genes per person A gene is on average about 3 000 base pairs What do genes do Genes DO NOT code for behaviors Genes code for the production of proteins Proteins Organic compounds essential to life implicated in many body and brain processes laborers Proteins are chains of amino acids Amino acids coded by 3 contiguous base pairs or codons 20 different AAs How does coding work While genes do in fact code for proteins 90 of each gene is non coding So if a gene is on average 3000 bp long only 300 actually code for proteins Exons Parts that code codes for proteins Introns Parts that don t code Coding means providing the instructions to the creation of a protein Not direct Ex Recipe book doesn t bake the cake Steps from DNA Protein Transcription Translation Transcription where genes duplicate themselves onto messenger ribonucleic acid mRNA Only exons are retained for mRNA mRNA is single strand not double Uracil U in place of Thymine T After duplication mRNA leaves cell nucleus DNA never leaves the nucleus mRNA leave the nucleus Steps from DNA Protein Transcription Translation Translation mRNA meets up with and attaches to ribosome in the cytoplasm Ribosome Protein factory Cytoplasm Space between cell nucleus and wall Ribosome works with tRNA transfer RNA to read mRNA and create amino acids On average 400 amino acids make a protein Human Genetic Variation Differences in DNA sequence which proteins are manufactured variation in phenotypes Still different proteins are not necessarily functionally different in the cell How do we all end up with different DNA Inherited on thread like structures called chromosomes Video The Human Genome Project 3D Animation http www youtube com watch v VJycRYBNtwY Process of Inheritance 23 chromosomes inherited from each parent 43 in all One pair 2 are sex chromosomes F XX or M XY Genes located on a specific part of a specific chromosome ex chromosome 5 b p 1 349 4 126 b p base pair Maternal and paternal chromosomes that are homologous matching have same combinations of genes in the same order but the nucleotides can differ Nucleotide is the same thing as a base Chromosome vs DNA people who sit in them REMEMBER A gene is like a row of empty seats The nucleotides like the Chromosomes are basically pieces of DNA inherited on threads that are tightly coiled in order to fit in the cell nucleus All DNA uncoiled in a straight line 6ft Genetic Polymorphisms Often maternal and paternal copies of genes are the same For most genes there is only one version for all humans Alternative copies of a gene are called alleles About 1 10 of genes have variants ex Ab AB aB ab Genes with two or more possible alleles are called genetic polymorphisms 3 types of Polymorphisms Single Nucleotide Polymorphism SNP Most common type 90 of all Due to single difference in nucleotide base Slight change may or may not result in different amino acid being produced Microsatellites Minisatellites One allele is longer than the other more base pair repeats Same as micro but larger blocks of b p repeats Allelic v Phenotypic Difference Sometimes allelic difference does not result in phenotypic differences Why How do allelic differences result in behavioral differences Effects are probabilistic not deterministic Ex lets say Gene Z has two possible alleles to inherit A or a Perhaps A increases your aggression by 3 and a decreases it by 1 Inheritance Revisited Which allele you inherit from your parents is random Remember your parents have two alleles on each gene but you only inherit a single chromosome from each parent for each of the 23 chromosomes Inherited through gametes sperm and egg cells These cells are different in that they only contain a random half of parents genetic material Different Genetic Effects Monogenic one gene one phenotype Ex Sickle cell anemia Polygenic possession of certain alleles can increase or decrease odds of the phenotype Pleiotropy a single gene effects various phenotypes Ex DAT1 associated with delinquency and number of sex partners Polymorphisms for Antisocial Behaviors Most candidate genes for ASB involve neurotransmission Brain comprised of billions of nerve cells or neurons Neurons communicate through electrical impulses that stimulate release of chemical messengers called neurotransmitters Neurotransmitters cross gap synapse between neurons The problem with neurotransmitters Some amount of neurotransmitters inevitably get left behind in the synapse How much gets eliminated determined by Transporter protein reuptake collects leftovers and returns them to pre synaptic neuron Enzymes break down neurotransmitters left in synapse into inactive particles neuron Receptor protein builds receptor sights Exist on post synaptic Receptor sights are neurotransmitter specific ex Dopamine can only go to dopamine receptor Video Function of Neurotransmitters http www youtube com watch v haNoq8UbSyc What s a gene got to do with it Different polymorphisms correspond to different efficiency in Reuptake process Enzymes metabolizing process Post synaptic reception of neurotransmitter Genes most relevant for criminal behavior include Dopaminergic genes Serotonergic genes Dopamine v Serotonin Dopamine Excitatory neurotransmitter Baseline levels vary from person to person Largely a function of genes High baseline levels more risky behavior Serotonin Inhibitory neurotransmitter Regulates behavioral impulses
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