Test 2 NotesPower 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 PairsA 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 à 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 à 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 à which proteins are manufactured à 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=VJycRYBNtwYProcess 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: REMEMBER: A gene is like a row of empty seats. The nucleotides like the people who sit in them. 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 One allele is “longer” than the other (more base pair repeats) Minisatellites 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 è 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. Receptor protein: builds receptor sights. Exist on post synaptic neuron.  Receptor sights are neurotransmitter specific. (ex. Dopamine