The Inheritance of Traits: Genes, Diversity, and Genetic Diseases

1. Chapter 5 Are You Only as Smart as Your Genes?Mendelian and Quantitative Genetics 0

2. 1 The Inheritance of Traits Offspring resemble their parents, but not exactly. Siblings resemble each other, but not exactly. How much is because of environment? How much is inherited?

3. 1 The Inheritance of Traits The human life cycle: Adults produce gametes in their gonads by meiosis. Sperm cells fertilize egg cells to form single-celled zygotes. Repeated cell divisions form the embryo.

4. 1 The Inheritance of Traits The human life cycle, cont.: The embryo grow to become a fetus. After birth, the individual continues to grow until reaching adulthood.

5. 1 The Inheritance of Traits Genes are segments of DNA that code for proteins. Analogous to words in an instruction manual for building a human Chromosomes are analogous to pages in the instruction manual. Each “page” contains thousands of “words” Different types of cells use different words, in different orders

6. 1 The Inheritance of Traits - Producing Diversity in Offspring Mistakes in copying DNA (mutations) produce different versions of genes (alleles), with different results.

7. 1 The Inheritance of Traits - Producing Diversity in Offspring Parent cell has two complete copies of the manual: 23-page copy from mom and 23-page copy from dad 23 pairs of homologous chromosomes

8. 1 The Inheritance of Traits - Producing Diversity in Offspring Segregation: in meiosis, one member of each homologous pair goes into a gamete Gamete gets just one copy of each page of the manual Independent assortment randomly determines which member of a pair of chromosomes goes into a gamete This is due to random alignment during metaphase I About 8 million different combinations of chromosomes.

9. 1 The Inheritance of Traits - Producing Diversity in Offspring Due to independent assortment, the instructions in one sperm cell is an unique combination of pages.

10. 1 The Inheritance of Traits - Producing Diversity in Offspring Random fertilization produces more diversity: 64 trillion possibilities! No two humans are genetically identical, except for monozygotic twins. Dizygotic twins are 50% identical just like siblings born at different times.

11. 2 Mendelian Genetics: When the Role of Genes Is Clear Gregor Mendel: first to accurately describe rules of inheritance for simple traits His research involved controlled mating between pea plants. His pattern of inheritance occurs primarily in traits that are due to a single gene with a few alleles. Mendel’s principles also apply to many genetic diseases in humans.

12. 2 Mendelian Genetics: When the Role of Genes Is Clear Phenotype: physical traits of an individual Genotype: description of the alleles for a particular gene in an individual Homozygous (-ote): both alleles for a gene are identical Heterozygous (-ote): the gene has two different alleles Recessive: the phenotype of an allele is seen only when homozygous Dominant: the phenotype is seen when homozygous or heterozygous

13. 2 Mendelian Genetics - Genetic Diseases in Humans Cystic fibrosis: a recessive human genetic disease Defect in chloride ion transport Causes recurrent lung infections, dramatically shortened lifespans Heterozygotes (carriers) do not show the symptoms Most common recessive disease among Europeans

14. 2 Mendelian Genetics - Genetic Diseases in Humans Huntington’s disease: a dominant human genetic disease Progressive, incurable, always fatal Symptoms occur in middle age Mutant protein forms clumps inside nerve cell nuclei, killing the cells Having a normal allele cannot compensate for this

15. 2 Mendelian Genetics - Using Punnett Squares to Predict Offspring Genotypes Punnett square: graphic way to predict possible outcomes of a cross Consider a cross between two cystic fibrosis carriers “F” = normal allele; “f” = recessive disease allele The cross would be: F f x F f What offspring could result?

16. 2 Mendelian Genetics - Using Punnett Squares to Predict Offspring Genotypes

17. Animation: Mendel’s Experiments Click “Go to Animation” / Click “Play”

18. 2 Mendelian Genetics - Using Punnett Squares to Predict Offspring Genotypes Dihybrid crosses are crosses that involve two traits. The first step in a dihybrid is to determine the possible gametes. Yellow (Y) is dominant to green (y) and Round (R) is dominant to wrinkled (r). If you cross YyRr x YyRr, Possible gametes for parent 1 are YR, Yr, yR, yr Possible gametes for parent 2 are YR, Yr, yR, yr

19. 2 Mendelian Genetics - Using Punnett Squares to Predict Offspring Genotypes • The results of the cross results in a 9:3:3:1 phenotypic ratio.

20. 3 Quantitative Genetics: When Genes and Environment Interact Quantitative traits show continuous variation: Large range of phenotypes E.g., height, weight, intelligence Variation due to both genetic and environmental differences

21. 3 Quantitative Genetics: When Genes and Environment Interact Mean: sum up all the phenotypic values and divide by the number of individuals; same as the average. Variance: a measure of how much variability there is in the population

22. 3 Quantitative Genetics - Why Traits Are Quantitative Quantitative traits, with continuous variation, are polygenic traits. Result of several genes Each with more than one allele Interaction of multiple genes with multiple alleles results in many phenotypes. Example: human eye color Heritability: proportion of the variation within a population due to genetic differences among individuals

23. 3 Quantitative Genetics - Calculating Heritability in Human Populations Have to use correlation to measure heritability in humans Scientists seek “natural experiments,” situations in which either the overlap in genes or environment is removed Twins are often used Monozygotic twins share all their genes and their environment Dizygotic twins share environment, but only half their genes Heritability of IQ from such twin studies estimated to be about 0.52

24. 3 Quantitative Genetics - Calculating Heritability in Human Populations Twins share a more similar environment than most humans Similar treatment of twins might explain why their IQs are so similar Monozygotic twins raised apart share all genes but are treated like everyone else Estimates of IQ heritability for such twins is 0.72 Drawback: limited number of such twins to study Table 7.2 discusses IQ heritability

25. 4 Genes, Environment, and the Individual - The Use and Misuse of Heritability Differences between groups may be environmental, despite a high heritability A heritability value pertains just to the population in which it was measured, and to the environment of that population Imagine a laboratory population of mice of varying weights Divide this population into 2 genetically identical groups Give one group a rich diet, the other a poor diet The “rich diet” mice will be bigger than the “poor diet” mice.

26. 4 Genes, Environment, and the Individual - The Use and Misuse of Heritability Allow the mice in each group to breed, maintaining their diets. Measure the weight of adult offspring; correlation with parents shows high heritability.

27. 4 Genes, Environment, and the Individual - The Use and Misuse of Heritability Instead of body weight in mice, consider IQ in humans. Affluent group: higher IQs Impoverished group: lower IQs Conclude that the difference is probably due to genetics?

28. 4 Genes, Environment, and the Individual - The Use and Misuse of Heritability A highly heritable trait can still respond to environmental change. Maze-learning ability is highly heritable in rats. Bright rats have bright offspring Dull rats have dull offspring Still, no rats learned well in a restricted environment. All rats learned better in an enriched environment.

29. 4 Genes, Environment, and the Individual - The Use and Misuse of Heritability Heritability does not tell us about individual differences. Heritability is based on variances in populations. High heritability value for a trait does not automatically mean that most of the difference between two individuals is genetic.

30. 4 Genes, Environment, and the Individual - How Do Genes Matter? Genes have a strong influence on even complex traits. But, independent assortment of multiple genes with multiple alleles produces a large number of phenotypes. Environment can also have big effects. For quantitative traits, it is difficult to predict the phenotype of children from the phenotypes of the parents.

31. Genes are segments of DNA that code for ________. proteins centromeres carbohydrates karyotypes

32. Genes are segments of DNA that code for ________. proteins centromeres carbohydrates karyotypes

33. Genes are comparable to________. words in an instruction manual pages in an instruction manual copy of pages in an instruction manual appendix in an instruction manual

34. Genes are comparable to________. words in an instruction manual pages in an instruction manual copy of pages in an instruction manual appendix in an instruction manual

35. Which of these events does not contribute to unique combinations of alleles? mutations independent assortment random fertilization cell cycle checkpoints

36. Which of these events does not contribute to unique combinations of alleles? mutations independent assortment random fertilization cell cycle checkpoints

37. True or False: Monozygotic twins occur when two separate eggs fuse with different sperm. True. False.

38. True or False: Monozygotic twins occur when two separate eggs fuse with different sperm. True. False.

39. A pea plant has one recessive allele for wrinkled seeds and one dominant allele for smooth seeds. What will the pea plant look like? wrinkle smooth half wrinkled, half smooth not enough information to tell

40. A pea plant has one recessive allele for wrinkled seeds and one dominant allele for smooth seeds. What will the pea plant look like? wrinkle smooth half wrinkled, half smooth not enough information to tell

41. Two heterozygotes mate. What are the odds that their offspring will be homozygous recessive? 100% 75% 50% 25%

42. Two heterozygotes mate. What are the odds that their offspring will be homozygous recessive? 100% 75% 50% 25%

43. Which trait is a quantitative trait that does not show continuous variation? height skin color presence or absence of a widow’s peak intelligence

44. Which trait is a quantitative trait that does not show continuous variation? height skin color presence or absence of a widow’s peak intelligence

45. Does nature or nurture play a bigger role in determining who we are? nature nurture they both play a large role

46. Does nature or nurture play a bigger role in determining who we are? nature nurture they both play a large role

47. The Punnett square shown here illustrates the outcome of a cross between a man who carries a single copy of the dominant Huntington’s disease allele and an unaffected woman. What are the odds that Huntington’s disease will not be passed to this offspring? 100% 75% 50% 25%

48. The Punnett square shown here illustrates the outcome of a cross between a man who carries a single copy of the dominant Huntington’s disease allele and an unaffected woman. What are the odds that Huntington’s disease will not be passed to this offspring? 100% 75% 50% 25%

49. This Punnett square illustrates the likelihood that a woman who carries the cystic fibrosis allele would have a child with cystic fibrosis if the sperm donor were also a carrier. What are the odds that this offspring will have cystic fibrosis? 100% 75% 50% 25%

50. This Punnett square illustrates the likelihood that a woman who carries the cystic fibrosis allele would have a child with cystic fibrosis if the sperm donor were also a carrier. What are the odds that this offspring will have cystic fibrosis? 100% 75% 50% 25%