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Chapter 3

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Psychology 1000
Wolfgang Lehmann

Change to the quizzes More questions – closer to what you may see on the exam The midterm will not be as easy as what we’ve been getting in the quizzes There are a series of tougher questions on MyLearning for prep stuff. Genes, Evolution and Environment What do they have to do with psych? - Genes can “program” people to act a certain way - Certain disorders may be caused by a change in the gene - Predisposition (more susceptible) to… being an alcoholic o The environment triggers it Genes or Environment - A rectangle is four sides – two of each are parallel and two are longer than the others. But they equally contribute to the rectangle. Genes Jeans Functional units of heredity Composed of DNA Specify the structure of proteins Located on chromosomes Genes are transmitted to the next generation. Genes lead to the making of proteins – proteins make cells. Cells make every living thing. ANALOGY TIME: Genes are recipes – like for chocolate cake :3 Chromosomes Rod-shaped and found in the nucleus of every cell Sperm cell and each egg cell contain 23 chromosomes (human) Fertilized egg contains 46 arranged in pairs Made of DNA Genes Chromosomes contain thousands of genes - Human ~ 35,000 genes (or recipes) Genes are made of four amino acids - Guanine - Cytosine - Adenine - Thymine Chromosomes are made of two DNA strands – you have a ladder. Each side is a strand of DNA. The ladder is made of steps connecting the two sides – made of bases which are combinations of two amino acids. You twist it and then you end up with a big twisted elastic band made of DNA. Or it’s a book – the cover and the back cover thing and in the middle are the pages (which are the amino acids. Each step is a page made of two amino acids. If it was a recipe book – can a recipe take more than one page? – the gene can be several pages (or bases) long. Comparative Sequence Sizes (Bases) Yeast (chromosome 3) - 350 thousand Smallest human chromosome(Y) - 50 million Largest human chromosome (I) - 250 million Entire human genome - 3 billion A gene is a series of pages that makes a recipe. When the protein is made, the coil unravels and a copy of the recipe will be made. Some pages (bases) are more important than others. Some are active and some are not. The genotype dictates the proteins (recipes) that will be made. They end up as the phenotype (what we can observe) – lead to different features or traits. Small Differences can Count for a lot Small genetic sequence differences can have major impact on the expression of genes - Changes transcription factors and the making of proteins - Alters growth periods of the brain There is a 1.5% difference between a chimpanzee and a human Genetic of Chromosomal Anomalies 4% of all pregnancies suffer from chromosomal abnormalities Majority = miscarriages Only 0.5% of born babies have chromosomal abnormality - Many die soon after birth - Of those that survive, most suffer from Down syndrome Mutations can be beneficial, but they’re not usually. Most often they lead to mental deficit, physical abnormalities. Down’s Syndrome – Trisomy 21 - Usually, humans have 23 pairs of chromsomes - In this case, 3 for chromosome 21 o Gene mutation (egg or sperm) 1/691 live births Women who have children older are more at risk, but men can pass it on too. Distinct physical signs - Short and stocky stature - Oval, upward slanting eyes Lower IQ - Most can read, write and do math Mortality around age 40 is high - Brain degenerated looks like late stage Alzheimer’s Heredity and Evolution Heritability Measures the total proportion of variance in a trait that is due to genetic variance Looking at what is transmitted or inherited Genes vs Environment calculation  Score:  0 = environment  1 = genetic Not precise, but can be influenced by a number of things How is a trait more likely to get transmitted? Artificial selection The process of humans selecting certain variety of traits of an organism of others Is this often the case? Let’s consider the case of the dogs… Take the smallest poodles and breed til you get a miniature. Artificial Selection and Psych Why would artificial selection be beneficial to psych? Could it be used to understand the genetic basis of behaviour and disorders? How? Alcoholism Alcoholism has long been considered to be due in part to genetic factors For instance, children of alcoholics are more likely to also become alcoholics Need for an animal model to determine the contributing genes. Rats and Alcohol Need a strain of rats that drink large amounts of alcohol Need another strain that drinks very little Enables for genetic comparison How do we get those strains? Through artificial selection or selective breeding How would you start it? $100 to buy vodka and $900 to buy rats. How do you divide the rats? Give them each a cage with alcohol in it – measure the bottle. Take a large group of rats and determine the high and the low alcohol drinkers – very far away from the average. Ignore the rest. Breed th
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