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CHAPTER 3 GENES, ENVIRONMENT, AND DEVELOPMENT

CHAPTER 3 GENES, ENVIRONMENT, AND DEVELOPMENT. Learning Objective. What do evolution and species heredity contribute to our understanding of universal patterns of development?. Species Heredity. Genetic endowment that members of a species have in common

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CHAPTER 3 GENES, ENVIRONMENT, AND DEVELOPMENT

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  1. CHAPTER 3 GENES, ENVIRONMENT, AND DEVELOPMENT

  2. Learning Objective • What do evolution and species heredity contribute to our understanding of universal patterns of development?

  3. Species Heredity • Genetic endowment that members of a species have in common • Reason that certain patterns of development and aging are universal • Examples • Walk and talk around 1 year of age • Sexual maturation from 12-14 • Wrinkling of skin in 40s and 50s

  4. Darwin’s Theory of Evolution • Species heredity explained by evolutionary theory • Main arguments of Darwin’s theory • There is genetic variation in a species • Some genes aid adaptation more than others do • Adaptive genes passed on more frequently • Evolution is about the interaction between genes and environment

  5. Modern Evolutionary Perspectives • Human development influenced by a shared species heredity that evolved through natural selection • Human development also influenced by cultural evolution • Humans inherit a characteristically human environment and learn methods of adapting to the environment • Cultural evolution is based on learning and socialization

  6. Learning Objectives • What are the basic elements and processes of individual heredity, including genes, chromosomes, formation of a zygote, mitosis, and meiosis? • What has the Human Genome Project contributed to our understanding of human development?

  7. Individual Heredity –The Genetic Code • Conception – new cell nucleus formed from genetic material of ovum and genetic material of sperm • New cell is the zygote • Each parent contributes 23 chromosomes, 46 total, organized into 23 pairs • Chromosomes - threadlike bodies in nucleus of each cell made up of genes

  8. Individual Heredity –The Genetic Code • Sperm and ova each have only 23 chromosomes because they are produced through the cell division process of meiosis • A reproductive cell (in ovary or in testis) splits to form two 46-chromosome cells • The two cells split again to form a total of four cells, each of which receives 23 chromosomes • In the female, results in three nonfunctional cells and one ovum • In the male, results in four sperm

  9. Individual Heredity –The Genetic Code • The single-cell zygote becomes a multiple-cell organism through the process of mitosis • A cell (and each of its 46 chromosomes) divides to produce two identical cells, each containing the same 46 chromosomes • Following conception, through mitosis, the zygote divides into two cells, then into four cells, then into eight cells, etc. • Mitosis continues throughout life

  10. Individual Heredity –The Genetic Code • Except for ova and sperm, all normal human cells contain copies of the 46 chromosomes received at conception • Both members of a chromosome pair influence the same characteristics • Chromosomes are strands of DNA • Deoxyribonucleic acid made up of sequences of adenine, cytosine, guanine, and thymine (A, C, G, and T) • Sequences are functional units - genes

  11. The Human Genome Project • Researchers mapped the sequence of the chemical units (A,C,G, and T) that make up the strands of DNA in a full set of human chromosomes • Human genome consists of genes that serve as a template for the production of particular proteins and DNA that regulates the activity of the protein-producing genes • 999 of 1,000 base chemicals are identical; only 1 of 1,000 accounts for human differences

  12. Learning Objectives • What factors account for genetic uniqueness? • How genetically similar are twins? • How is sex determined?

  13. Genetic Uniqueness and Relatedness • Genetic uniqueness of children of same parents due to crossing over, an aspect of meiosis • Before separation, pairs of chromosomes line up; when they cross each other, parts are exchanged • Crossing over increases the number of distinct sperm or ova an individual can produce

  14. Genetic Uniqueness and Relatedness • Genetic similarity of parent and child • An individual receives half her chromosomes and genes from her mother and half from her father • Genetic similarity of siblings • Siblings receive half their genes from the same mother and half from the same father, but meiosis determines the genes actually received • Siblings share half their genes, on average

  15. Genetic Uniqueness and Relatedness • Identical twins or monozygotic twins (or identical triplets, etc.) • Genetically the same • Result when one fertilized ovum divides to form two or more genetically identical individuals • Fraternal twins or dizygotic twins • Result from release of two ova and fertilization by two sperm • As genetically alike as siblings

  16. Determination of Sex • Of the 23 pairs of chromosomes • 22 pairs - autosomes • 23rd pair - sex chromosomes • In males, the 23rd pair consists of a long chromosome (X) and a short chromosome with fewer genes (Y) • Females have two X chromosomes • Fathers determine a child’s sex • If a sperm carries a Y chromosome, the XY zygote is a genetic male • If a sperm carries an X chromosome, the XX zygote is a genetic female

  17. Caption: Chromosomes in each cell consist of strands of DNA

  18. Learning Objective • How are genes translated into physical and psychological characteristics?

  19. Translation and Expression of the Genetic Code • Environmental influences combine with genetic influences to determine how a genotype is translated into a phenotype • Genotype • The genetic makeup a person inherits • Phenotype • The characteristics or traits that are expressed • Gene expression • Activation of particular genes in particular cells at particular times; guided by genetic influences and affected by environmental factors

  20. Learning Objectives • What are the mechanisms by which traits are passed from parents to offspring? • What is an example of how a child could inherit a trait through each of these three mechanisms?

  21. Mechanisms of Inheritance:Single Gene-Pair Inheritance • Single gene-pair inheritance • Pattern described by Gregor Mendel • Human characteristics influenced by one pair of genes (one from mother, one from father) • A dominant gene trait will be expressed • A recessive gene trait will be expressed only when the gene is paired with another recessive gene for the trait

  22. Caption: Can you curl your tongue?

  23. Mechanisms of Inheritance:Sex-Linked Inheritance • Sex-linked characteristics are influenced by single genes located on sex chromosomes • Actually X-linked because most attributes are associated with genes on the X • Y chromosomes are smaller and have fewer genes to serve as counterpart or to dominate • Example: if a boy inherits a recessive color-blindness gene on the X, there is no color vision gene on the Y to dominate the color-blindness gene

  24. Mechanisms of Inheritance:Sex-Linked Inheritance • A female who inherits a color-blindness gene usually has a normal color-vision gene on her other X chromosome that can dominate the color-blindness gene • If a female is to be color-blind, she must inherit the gene on both Xs • Hemophilia is another condition that illustrates the principles of sex-linked inheritance

  25. Caption: X-linked inheritance

  26. Mechanisms of Inheritance:Polygenic Inheritance • Traits such as height, weight, intelligence, personality, and susceptibility to cancer and depression are polygenic • Influenced by multiple pairs of genes interaction with environmental factors • Many degrees of expression are possible in polygenic traits • Traits tend to be distributed in the population according to the normal curve

  27. Learning Objectives • How do genetic mutations occur? • How do mutations affect development? • What are the most common chromosomal abnormalities? • When chromosomal abnormalities occur, how do they affect development?

  28. Mutations • Mutation • A change in gene structure or arrangement that produces a new phenotype • May be harmful or beneficial depending on their nature and the environment • Example: sickle-cell disease • Can be inherited by offspring

  29. Chromosomal Abnormalities • Chromosomal abnormalities occur when there are errors in chromosome division during meiosis • The ovum or sperm will have too many or too few chromosomes • Chromosomal abnormalities are the main source of pregnancy loss

  30. Examples of Chromosomal Abnormalities • Down syndrome or trisomy 21 • 21st chromosomes = 3 • Children have distinctive physical characteristics and typically are classified as having some degree of mental retardation • Associated with older age of parents

  31. Examples of Chromosomal Abnormalities • Chromosomal abnormalities that involve a child receiving too few or too many sex chromosomes • Consequence of errors in meiosis or damage from environmental hazards • Turner syndrome – a female born with a single X chromosome (XO) • Klinefelter syndrome – a male born with one or more extra X chromosomes (XXY) • Fragile X – one arm of the X is only barely connected

  32. Caption: Photo of X chromosome with fragile X problem

  33. Learning Objectives • What methods are used to screen for genetic abnormalities? • What are the advantages and disadvantages of using such techniques to test for prenatal problems? • What are some abnormalities that can currently be detected with genetic screening?

  34. Genetic Diagnosis and Counseling • Genetic counseling • A service that helps people understand and adapt to the implications of genetic contributions to disease • Carriers do not have the disease but can transmit the gene for it to their children

  35. Issues in Genetic Diagnosis and Counseling • Sickle-cell disease • Sickle-shaped blood cells cluster together and distribute less oxygen through the circulatory system • If parents are carriers of the recessive gene for sickle-cell disease • Have 25% chance of having a child with sickle-cell disease • Have a 50% chance of having a child who will be a carrier

  36. Issues in Genetic Diagnosis and Counseling • Huntington’s disease • Associated with a single dominant gene • Strikes in middle age and disrupts the nervous system • Child of a parent with Huntington’s disease has a 50% chance of developing the disease • Discovery of gene for Huntington’s on chromosome 4 led to a test that can reveal if a person has inherited the gene

  37. Learning Objectives • What methods do scientists use to discern the contributions of heredity and environment to physical and psychological traits? • What are the strengths and weaknesses of these methods? • How do scientists estimate the influences of heredity and environment to individual differences in traits? • How do genes, shared environment, and nonshared environment contribute to individual differences in traits?

  38. Genetic and Environmental Influences: Behavioral Genetics • Behavioral genetics • Study of the extent to which genetic and environmental differences contribute to differences in traits • Use heritability estimates • The proportion of all the variability in the trait within a large sample that can be linked to genetic differences among individuals • Variability that is not associated with genetic differences is associated with environmental and experiential differences

  39. Studying Genetic and Environmental Influences: Experimental Breeding • Selective breeding • Attempting to breed animals for a particular trait to determine whether the trait is heritable • Tryon bred maze-bright rats to demonstrate the influence of genetics upon maze-learning ability • Other animal breeding studies showed genetic contributions to activity level, emotionality, aggressiveness, etc.

  40. Studying Genetic and Environmental Influences: Twin, Adoption, and Family Studies • Twin studies • Studies of twins, both identical and fraternal, reared apart and together • Adoption studies • Are adopted children more similar to biological parents or to adoptive parents? • Family studies • Studies of siblings with different degrees of genetic similarity and varying environments

  41. Estimating Influences • Concordance rates • Statistical calculations to estimate the degree to which heredity and environment account for individual differences in a trait of interest • A trait is heritable if the concordance rates are higher for more genetically related than for less genetically related pairs of people • Correlation coefficients • Used when a trait (e.g., intelligence) can be present in varying degrees

  42. Estimating Influences • From correlations reflecting the degree of similarity between twins, behavioral geneticists can estimate the contributions to individual differences in emotionality from • Genes • Shared environmental influences • Common experiences • Nonshared environmental influences • Experiences unique to the individual

  43. Molecular Genetics • Analysis of genes and their effects • Useful in identifying the multiple genes that contribute to polygenic traits • Example: Alzheimer’s disease • Twin studies show heritability but the roles of specific genes have not been clarified

  44. Learning Objectives • How do genes and environments contribute to individual differences in intellectual abilities, personality and temperament, and psychological disorders? • What do researchers mean when they talk about the heritability of traits? • Which traits are more strongly heritable than others?

  45. Findings from Behavioral Genetics Research – IQ • Correlations highest in identical twins • Heritability of IQ is about .50 • Genetic differences account for 50% of variation in IQ and environmental differences for 50% • Genetic endowment appears to gain importance from infancy to adulthood as a source of individual differences in IQ • Shared environmental differences become less significant with age

  46. Findings from Behavioral Genetics Research – Temperament and Personality • Temperament • Tendencies to respond in predictable ways that serve as the building blocks of personality • Buss and Plomin (1984) reported average correlations of .50 - .60 between temperament scores of identical twins but scores for fraternal twins not much greater than zero • Conclusion: living in the same home does not generally make children more similar in personality • Shared environment influences are important but nonshared influences are more important

  47. Findings from Behavioral Genetics Research – Psychological Disorders • Schizophrenia • Concordance rate for schizophrenia in identical twin pairs is 48% and for fraternal twins the rate is 17% • 90% of children who have one parent with schizophrenia do not develop schizophrenia • This means that environmental factors contribute significantly • People inherit predispositions to develop disorders, not the disorder per se

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