Genetics Heritability Lecture 8 1 Be able to define genome Exam 3 Learning Objectives a All of our genes 20 000 30 000 b How our genes interact with each other and our environment 2 Understand the hierarchy in the genome e g chromosomes are made up of what Genes are made up of what a b largest Genome chromosomes genes DNA smallest Each nucleus contains 2 sets of the human genome 3 Be able to define behavioral genetics a Very small number of genes differ across people b c d 96 of our genes are the same Behavioral geneticists look at the things that differ To what degree are individual differences due to genetic and environmental factors 4 What are the controversies surrounding behavioral genetics a Eugenics someone will create a future race where we only allow certain people to reproduce has happened in the past b Genetic determinism behavior is genetically determined and you can t stop it gives people permission to behave a certain way i Genes and environment are interconnected interact 5 What are the three major questions asked by behavioral geneticists a What causes variability in a trait genes vs environment b Which environmental effects are important parents teachers peers c How do genes and environment interact 6 What is heritability a How much an individual difference is explained by genetic factors i Ex height if its 90 heritable then 10 of it is due to differences in the environment 7 Be familiar with the misconceptions about heritability and be able to recognize examples a CANNOT be applied to a single person i Height has 90 heritability in the population your specific height may be different But the population as a whole is 90 The difference can be attributed to our environmental differences or food sleep ii A single individual s height for example is not 10 due to their environment iii iv Heritability applies to a group It is more accurate to say that the variation between people in height is 10 due to the environment b Is NOT constant unchangeable i For the environment to cause differences there has to be differences in the environment ii The greater the differences in the environment the more the heritability goes down iii Heritability only applies to a population at one point in time differs according to environmental conditions iv The more similar the environment between people the higher the heritability will be c Heritability is NOT a precise statistic i Only as good as the sample used 8 Be able to list and define the four methods used in behavioral genetics a Selective Breeding can t be done ethically with humans i Only works if a desired trait is heritable ii If selective breeding for a trait is successful the trait is at least somewhat genetic b Family Studies i Correlates genetic similarity with personality similarity ii If a trait is heritable more genetic relatedness more similarity on traits 1 iii Siblings 50 iv Grandparents and Grandchildren 25 v Aunts and Uncles 25 vi Cousins 1st 12 5 vii viii ix Problem families share genes and environment 1 Family studies are never definitive c Twin studies If a trait is heritable then siblings will share those genes If they share an environment and the trait is not heritable they may still share the trait because of environment i Monozygotic identical twins share a single fertilized egg a single zygote 1 2 3 Share 100 of their DNA with their twin Shared placenta Share more genes if the trait is heritable they would be more likely to have it ii Dizygotic twins 1 Comes from two separately fertilized eggs 2 zygotes dizygotic 2 3 Separate placentas Share about 50 of their genes iii Equal Environments assumption environment experienced by identical twins no more similar than environments shared by fraternal twins d Adoption studies i Correlations on traits between adopted children and adoptive parents environmental influence ii Correlations between adopted children and genetic parents genetic influence iii Potential problem 1 Representativeness 2 Selective placement of adopted children iv Tend to be strong indicators of heritability v Adopted children aren t tremendously more similar to their biological siblings than their adopted sibblings e Ideal study i Twins reared apart combines strengths of twin and adoption studies 9 Know advantages and disadvantages associated with each method from behavioral genetics Controversy designer human selecting people on basis of their trait a b People worried it will lead to eugenics c d Having the knowledge won t lead to those type of activities e Has happened in history Some people can reproduce and others can t 10 Be able to compute heritability if I give you the correlations for monozygotic and dizygotic twins a The correlation coefficient should be higher among Identical mono twins than fraternal dizygotic twins if it is heritable because they share more genes If MZ twins are more similar than DZ twins on a given trait due to heritability b c DZ twins correlated at 18 for neuroticism d MZ twins correlated at 41 for neuroticism e Heritability 2 X difference in correlation f Heritability 2 X 41 18 g Heritability 2 X 23 46 h Heritability 46 11 Which kind of study generally gets higher heritability scores Adoption or twin studies a MZ twins are much more similar to each other than DZ twins b But adopted children aren t tremendously more similar to their biological siblings than their adopted siblings 2 There might be something special about having ALL your genes in common with someone c d Higher heritability twin studies e Lower adoption studies 12 What is nonadditive genetic variance It s how genes interact that cause a behavior 50 of your genes interact need 100 to have the same behavior because the genes interact with each other a Genes don t just cause a behavior b c d Genes may not influence traits in a linear additive way but rather combine and interact in a configural pattern in which all components are essential and the absence of or a change in any one gene can produce qualitative or a large quantitative change in the result So if 2 individuals DZ twins or bio siblings share only 50 common genes they may be less than half as similar to each other as are two individuals MZ twins who are 100 of genes because genes influence traits in a non additive fashion 100 is in a sense 2 X as large as 505 e 13 Be familiar with the heritability of the extraversion neuroticism drinking and alcoholism 9be able to calculate heritability Extra 40 60 heritable a b Neuroticism 30 54 heritable c
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