Genes and ProteinsLecture 2

PSY391SJohn Yeomans

Why Use Genes?Behavior = Genes EnvironmentPsychologists have studied environmental effects on behavior best for a century.Human genome project now gives us all the genes. What an opportunity!Most of these genes are found in lower animals such as mice.Behavioral effects of single genes can be studied in mice and humans.

DNA4 Bases: Cytosine and guanine, adenine and thymine.Deoxyribose backbones hold 2 complementary chains each with full information.Can separate and then self-replicate.Hold all genetic information in higher animals.Human genome 3.1 billion bases (2000).

Messenger RNASingle chain with 4 bases, C, G, A and uracil instead of T.Ribose backbone.Transcribed from DNA in nucleus, then spliced (edited), then translated into proteins by ribosomes in cytoplasm.

ProteinsSingle chain of 20 amino acids.1 Codon: 3 bases1 amino acid.Start (AUG) and stop codons.Genes (about 25,000) and pseudogenes.Folding of proteins into complex 3D structurescomplex functions.Trafficking of proteins into many different cell sites.

What is a Gene?A DNA sequence that codes for 1 protein.Hard to count genes. First, find start and stop codons. Exons and introns--Junk DNA?But some fragments dont work as proteins--Pseudogenes.No agreement on exact number.

Gene TechnologyCutting DNA with restriction enzymes.Measuring lengths with gel electrophoresis.Copying DNA by cloning or PCR.Automated sequencing by computer (Mbases per day)Complete genomes of hundreds of species.

Functional StudiesHybridization of DNA and RNA.Blotting to find specific chains: Southern-DNA, Northern-RNA, Western-proteins.In situ hybridization: Find RNA in brain.Immunocytochemistry: Find proteins in brain.

ChromosomesLecture 3PSY391SJohn Yeomans

Mutations, Chromosomes and Genetic DiseasesLecture 3 PSY391SMutantsChromosomesChromosome DisordersGene DisordersLinkage of Genes to DiseasesGene Therapy and Ethics

MutantsRandom mutations: spontaneous, or induced by chemicals (ENU) or radiation.Targetted mutations of single genes: transgenic--added copies; knockouts--deleted copies.Flies and mice used commonly.About 1/3 of behavioral neuroscience now studies of mutants, especially mice.

Knockout MiceSedivy & Joyner,1992

Chromosomes

Chromosome Bands

Chromosome MapsBreaks and Crossovers: Genes are linked on each chromosome by distance.Morgan: Use linkage to map gene distances on each chromosome--cM.Genome Projects: Each Ch mapped in megabases (Mb).Genetic diseases can be mapped by distance from markers!

HGP Map

Chromosome DisordersExtra Chromosome: trisomy 21 (Downs syndrome), trisomy 18.Deletions: 5p- (Cri du chat), 7q- (Williams)Breaks: Fragile XMost large chromosome additions and deletions are lethal and lead to spontaneous abortions.

Neurogenetic DisordersHuntingtons: extra CAG repeats on 4p.Fragile X: extra CGG on X.Alzheimers: point mutations on Ch1, 21 etc.Recessive and DominantDisease Gene Searches: Chromosome link, to gene link, to base change links.Animal Models of Disease.

Gene Therapy and EthicsSpontaneous AbortionsAmniocentesis and CounsellingLife PlanningAdult Gene Therapy?Future of Species?