Transcript Lecture 2 PSY391S John Yeomans

Genes and Proteins
Lecture 2
PSY391S
John Yeomans
Why Use Genes?
• Behavior = Genes <=> Environment
• Psychologists 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.
DNA
• 4 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 RNA
• Single 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.
Proteins
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Single chain of 20 amino acids.
1 Codon: 3 bases1 amino acid.
Start (AUG) and stop codons.
Genes (about 25,000) and pseudogenes.
Folding of proteins into complex 3D
structurescomplex 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 don’t work as
proteins--Pseudogenes.
• No agreement on exact number.
Gene Technology
• Cutting 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 Studies
• Hybridization of DNA and RNA.
• Blotting to find specific chains: SouthernDNA, Northern-RNA, Western-proteins.
• In situ hybridization: Find RNA in brain.
• Immunocytochemistry: Find proteins in
brain.
Chromosomes
Lecture 3
PSY391S
John Yeomans
Mutations, Chromosomes and
Genetic Diseases
Lecture 3 PSY391S
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Mutants
Chromosomes
Chromosome Disorders
Gene Disorders
Linkage of Genes to Diseases
Gene Therapy and Ethics
Mutants
• Random 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 Mice
Sedivy & Joyner,
1992
Chromosomes
Chromosome Bands
Chromosome Maps
• Breaks 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 Disorders
• Extra Chromosome: trisomy 21 (Down’s
syndrome), trisomy 18.
• Deletions: 5p- (Cri du chat), 7q- (Williams’)
• Breaks: Fragile X
• Most large chromosome additions and
deletions are lethal and lead to
spontaneous abortions.
Neurogenetic Disorders
• Huntington’s: extra CAG repeats on 4p.
• Fragile X: extra CGG on X.
• Alzheimer’s: point mutations on Ch1, 21
etc.
• Recessive and Dominant
• Disease Gene Searches: Chromosome
link, to gene link, to base change links.
• Animal Models of Disease.
Gene Therapy and Ethics
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Spontaneous Abortions
Amniocentesis and Counselling
Life Planning
Adult Gene Therapy?
Future of Species?