Exam 3 Learning Objectives Genetics Heritability Lecture 8 1 Be able to define genome Genome is the complete set of genetic information for an organism It can be thought of as a blueprint or set of instructions for building an organism Each species has its own genome The human genome is spread across 23 chromosomes which hold our DNA or genetic code 2 Understand the hierarchy in the genome e g Chromosomes are made up of what Genes are made up of what a In the nucleus of each cell the DNA molecule is packaged into thread like structures called chromosomes Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure Chromosomes are not visible in the cell s nucleus not even under a microscope when the cell is not dividing However the DNA that makes up chromosomes becomes more tightly packed during cell division and is then visible under a microscope Most of what researchers know about chromosomes was learned by observing chromosomes during cell division b A gene is the basic physical and functional unit of heredity Genes which are made up of DNA act as instructions to make molecules called proteins In humans genes vary in size from a few hundred DNA bases to more than 2 million bases The Human Genome Project has estimated that humans have between 20 000 and 25 000 genes Every person has two copies of each gene one inherited from each parent Most genes are the same in all people but a small number of genes less than 1 percent of the total are slightly different between people Alleles are forms of the same gene with small differences in their sequence of DNA bases These small differences contribute to each person s unique physical features 3 Be able to define behavioral genetics It is the logic of twin and adoption studies undergirds research in the growing field a b Behavioral genetics is a scientific displace with roots in psychology genetics biology and related fields that explores the empirical evidence concerning the relative influences of genetic In recent years research in behavioral genetics has employed complex statically modeling procedures in which data from different families constellations and types are combined to test the hypotheses about nature and nurture c d Twin and adoption studies form the basis for many of the field s central findings about heritability of personality traits 4 What are the controversies surrounding behavioral genetics a Behavioral genetics To what degree are individual differences due to genetic environmental factors b Controversy Eugenics Genetic determinism Genes environment interact 5 What are the three major questions asked by behavioral geneticists a What causes variability in a trait genes vs environment b What environmental effects are important e g parents teachers peers c How do genes and environment interact 6 What is heritability How much an individual difference is explained by genetics a How much are you like your father or your mother While our experiences and our situations have tremendous impacts on who we are how we act etc our genetic makeup is also important in determining these factors Therefore our heritability or the extent to which differences in a trait can be attributed to our genetic makeup is important in trying to understand human behavior Also keep in mind that genes and environment do not occur in isolation but interact with each other As a result you are who you are and you act and think the ways you do because of the combination of your heritability and your environment 7 Be familiar with the misconceptions about heritability and be able to recognize examples a Heritability CANNOT be applied to single people A single individual s height for example is not 10 due to their environment It is more accurate to say that the variation between people in height is 10 due to the environment Is NOT constant unchangeable Heritability only applies to a population at one point in time The more similar the environment between people the higher heritability will be Is NOT a precise statistic Only as good as the sample used 8 Be able to list and define the four methods used in behavioral genetics a Four methods Selective breeding Can t be done ethically with humans Only works if a desired trait is heritable If selective breeding for a trait is successful the trait is at least somewhat genetic Family studies 1 Correlates genetic similarity w personality similarity 2 If trait is heritable more genetic relatedness more similarity on traits 3 Problem 4 5 Family studies are never definitive Families share genes and environment Twin studies 1 Monozygotic twins 2 Share a single fertilized egg a single zygote monozygotic 3 Share 100 of their genes 4 Dizygotic twins 5 Come from two separately fertilized eggs two zygotes dizygotic 6 Share about 50 of their genes 7 Monozygotic vs Dizygotic twins 8 Estimate heritability 9 Are identical monozygotic MZ twins more similar than fraternal dizygotic DZ twins 10 If MZ twins are more similar than DZ twins on a given trait due to heritability 11 Neuroticism a DZ twins correlated at 18 b MZ twins correlated at 41 c Heritability 2XDifference in correlation d Heritability 2 41 18 e Heritability 2 23 46 f Heritability 46 g Do twin studies eliminate problem from family studies i Equal environments assumption ii Environment experienced by identical twins no more similar than environments shared by fraternal twins Adoption studies 1 Correlations on traits between adopted children and adoptive parents environmental influence 2 Correlations between adopted children and genetic parents genetic influence 3 Potential problem a Representativeness b Selective placement of adopted children 4 Ideal study a Twins reared apart b Combines strengths of twin and adoption studies MZ twins are MUCH more similar to each other than DZ twins But adopted children aren t tremendously more similar to their biological siblings than There might be something special about having ALL your genes in common with their adopted siblings someone Non additive genetic variance The Big Five o Extraversion 40 60 heritable o Neuroticism 30 54 heritable Drinking related to o Sensation seeking o Extraversion o Neuroticism o Drinking 36 56 o Alcoholism 50 71 9 Know advantages and disadvantages associated with each method from behavioral genetics 10 Know the difference between monozygotic and dizygotic twins a Monozygotic twins tend to be remarkably similar Not only do they very much alike
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