HEREDITARY INFLUENCES ON DEVELOPMENT

Transcription

1 HEREDITARY INFLUENCES ON DEVELOPMENT

2 HEREDITARY INFLUENCES ON DEVELOPMENT Genotype: genes that one inherits Phenotype: how one s genotype is expressed in observable or measurable characteristics

3 PRINCIPLES OF HEREDITARY TRANSMISSION Development begins at conception Sperm cell penetrates ovum Zygote is formed 46 chromosomes (23 from each parent) Genes, stretches of DNA» Provides biological basis for development

4 PRINCIPLES OF HEREDITARY TRANSMISSION Growth of Zygote, Production of Body Cells Zygote replicates through mitosis Each division duplicates chromosomes Each new cell contains the 46 we inherited at conception

5 Figure 2.1 Mitosis: the way that cells replicate themselves.

6 PRINCIPLES OF HEREDITARY TRANSMISSION The Germ Cells (produce sperm and ova) Production of Gametes through Meiosis Duplication of 46 chromosomes Crossing-over: adjacent chromosomes break and exchange segments of genes Pairs of duplicated chromosomes segregate into two new cells Cells divide, 23 single chromosomes

7 Figure 2.2 Diagram of the meiosis of a male germ cell.

8 PRINCIPLES OF HEREDITARY TRANSMISSION The Germ Cells Hereditary Uniqueness Independent assortment each chromosome pair segregates independently, resulting in genetic uniqueness

9 PRINCIPLES OF HEREDITARY TRANSMISSION Multiple Births Monozygotic twins: single zygote divides, are genetically identical Dizygotic (fraternal) twins: two ova released and fertilized by different sperm, are as genetically similar as any sibling pair

10 PRINCIPLES OF HEREDITARY TRANSMISSION Male or Female Karyotypes chromosomal portraits 22 pairs (autosomes) are similar in males and females 23 rd pair are the sex chromosomes Males X and Y (typically), Females 2 X s (typically) Ova contain X s, sperm an X or a Y Males determine sex of children

11 FOCUS ON RESEARH: CROSSING-OVER AND CHROMOSOME SEGREGATION DURING MEIOSIS During Meiosis Chromosomes duplicate Chromosomes swap genetic material at a chiasma 42 events during meiosis for females 27 events for males More likely at certain spots (hotspots) Increases genetic variability Chiasma reduces likelihood of aneuploidy:

12 FOCUS ON RESEARH: CROSSING-OVER AND CHROMOSOME SEGREGATION DURING MEIOSIS Meiosis Benefits Increases genetic variability Chiasma reduces likelihood of aneuploidy: incorrect number of chromosomes

13 Figure 2.3 A chromosome that had duplicated in preparation for meiosis. Used by permission of Julia Cline.

14 Figure 2.4 Recombination via crossing-over between homologous grandparent genes during meiosis and four of the 16 possible zygote combinations. Used by permission of Julia Cline.

15 PRINCIPLES OF HEREDITARY TRANSMISSION What Do Genes Do? Produce amino acids which produce enzymes and proteins necessary for creation and functioning of cells Guide cell differentiation Regulate the pace/timing of development Environmental factors (internal and external) influence how genes function

16 Table 2.1 Different Levels of Gene-Environment Interaction That Influence Genetic Expression Source: Adapted from Johnson, 2005.

17 PRINCIPLES OF HEREDITARY TRANSMISSION How are Genes Expressed? Single-Gene Inheritance Patterns Simple Dominant-Recessive Inheritance one pair of genes (alleles), one from each parent Either dominant or recessive Homozygous same alleles Heterozygous different alleles» Will then be a carrier for the recessive trait

18 Figure 2.5 Possible genotypes (and phenotypes) resulting from a mating of two heterozygotes for normal vision.

19 PRINCIPLES OF HEREDITARY TRANSMISSION How are Genes Expressed? Codominance Phenotype is a compromise between the dominant and recessive alleles Examples:» Blood Type» Sickle-cell trait

20 Figure 2.6 Normal (round) and sickled (elongated) red blood cells from a person with sickle -cell anemia.

21 PRINCIPLES OF HEREDITARY TRANSMISSION How are Genes Expressed? Sex-Linked Inheritance Genes located on sex chromosomes Most from recessive genes found only on X chromosomes (common in males) More than 100 sex-linked characteristics

22 Figure 3.7 Sex-linked inheritance of red/green color blindness. In the example here, the mother can distinguish reds from greens but is a carrier because one of her X chromosomes contains a color-blind allele. Notice that her sons have a 50 percent chance of inheriting the color-blind allele and being color-blind, whereas none of her daughters would display the trait. A girl can be color-blind only if her father is color blind and her mother is at least a carrier of the color-blind gene.

23 PRINCIPLES OF HEREDITARY TRANSMISSION How are Genes Expressed? Polygenic Inheritance Characteristics influenced by many pairs of alleles Most complex human attributes are polygenic

24 HEREDITARY DISORDERS Congenital defects present at birth (5%) Chromosomal Abnormalities too many or too few Sex Chromosome Abnormalities Abnormalities of the Autosome Down syndrome most common trisomy-21 (extra 21 st chromosome)

25 Figure 2.8 Sources of congenital defects.

26 Table 2.2 Four Common Sex Chromosome Abnormalities Sources: Robinson et al., 1992; Plomin et al., 1997; Shafer and Kuller, 1996.

27 HEREDITARY DISORDERS Genetic Abnormalities Many passed to children by parents who are carriers of recessive alleles Some are caused by dominant alleles Some result from mutations changes in structure of one or more genes Spontaneous Environmental hazards

28 Table 2.3 Brief Description of Major Recessive Hereditary Diseases. Sources: Kuller, Cheschier, & Cefalo, 1996; Strachan & Read, 1996.

29 HEREDITARY DISORDERS Predicting Hereditary Disorders Genetic counseling both chromosomal and genetic abnormalities Determine likelihood of transmitting disorder to children Obtain a pedigree family history DNA from parents blood Consider options based on risk

30 HEREDITARY DISORDERS Detecting Hereditary Disorders Amniocentesis withdrawal of a sample of amniotic fluid, tests fetal cells within fluid Risk of miscarriage higher than risk of birth defect in women younger than 35 Conducted 11 th - 14 th week of pregnancy Results two to three weeks later

31 Figure 2.9 In amniocentesis, a needle is inserted through the abdominal wall into the uterus. Fluid is withdrawn and fetal cells are cultured, a process that takes about 3 weeks. Adapted from Before We Are Born, 4 th ed., by K. L. Moore & T. V. N. Persaud, 1993, p. 89. Philadelphia: Saunders. Adapted with permission of the author and publisher.

32 HEREDITARY DISORDERS Detecting Hereditary Disorders Chorionic villus sampling collects cells from chorion Conducted 8 th - 9 th week of pregnancy Results in 24 hours Risk of miscarriage 1 in 50 Ultrasound sound waves provide outline of fetus useful after 14 th week, safe

33 Figure 2.10 Chorionic villus sampling can be performed much earlier in pregnancy, and results are available within 24 hours. Two approaches to obtaining a sample of chorionic villi are shown here: inserting a thin tube through the vagina into the uterus or a needle through the abdominal wall. In either of these methods, ultrasound is used for guidance. Adapted from Before We Are Born, 4 th ed., by K. L. Moore & T. V. N. Persaud, 1993, p. 89. Philadelphia: Saunders. Adapted with permission of the author and publisher.

34 HEREDITARY DISORDERS Treating Hereditary Disorders Special diets for metabolic disorders (PKU) Fetal surgery, hormone therapy Gene replacement therapy relieves symptoms, doesn t cure disorder Germline gene therapy replace harmful genes early in embryonic stage to cure defect; not yet used in humans (ethical issues?)

35 HEREDITARY INFLUENCES ON BEHAVIOR Behavioral genetics: study of how genotype interacts with environment to determine behavioral attributes Methods of studying hereditary influences Selective breeding animal studies Family studies examining kinship Twin design identical vs. fraternal Adoption design children similar to biological or adoptive parents?

36 Figure 2.11 Maze-running performance by inbred mazebright and mazedull over 18 generations. From Behavioral Genetics: A Primer, 3rd ed., by R. Plomin, J. C. DeFries, & G. E. McClearn, Copyright W. H. Freeman and Company.

37 HEREDITARY INFLUENCES ON BEHAVIOR Methods of studying hereditary influences Contribution of Genes and Environment Concordance rates - % of pairs of people who both display a trait if one member has it Gene Influences» Heritability coefficient = (r identical r fraternal) X 2 Nonshared Environmental Influences = 1-r(identical twins reared together) Shared Environmental Influences = 1 (H + NSE)

38 Figure 2.12 Concordance rates for homosexuality in 110 male twin pairs. From the higher concordance for the identical twin pairs, we can infer that genes influence one s sexual orientation. Based on A Genetic Study of the Male Sexual Orientation, by J. M. Bailey and R. C. Pillard, 1991, Archives of General Psychiatry, 48, Copyright 1991 by the Archives of General Psychiatry. Adapted by permission.

39 Figure 2.13 Concordance rates for identical and fraternal twins for several behavioral dimensions. From R. Plomin, M. J. Owen, and P. McGuffin, The genetic basis of complex human behaviors, Science, 264, Copyright 1994 by the American Association for the Advancement of Science. Reprinted by permission.

40 Table 2.4 Average Correlation Coefficients for Intelligence-Test Scores from Family Studies Involving Persons at Four Levels of Kinship. Source: Based on Family studies of Intelligence: A Review, by T. J. Bouchard Jr., & M. McGue, Science, 212, pp

41 HEREDITARY INFLUENCES ON BEHAVIOR Myths about Heritability Estimates Cannot tell us if we have inherited a trait Does not apply to individuals Differences among individuals due to differences in inherited genes Only apply to populations under particular environmental circumstances Clearly heritable traits CAN be modified by environmental influences

42 HEREDITARY INFLUENCES ON BEHAVIOR Hereditary Influences on Intellectual Performance As children age Role of genes increases Nonshared environment increases Shared environment decreases

43 Figure 2.12 Changes in the correlation between the IQ scores of identical and fraternal twins over childhood. From The Louisville Twin Study: Developmental Synchronies in Behavior, by R. S. Wilson, 1983, Child Development, 54, pp Copyright 1983 by The Society for Research in Child Development, Inc. Reprinted by permission.

44 HEREDITARY INFLUENCES ON BEHAVIOR Hereditary Contributions to Personality Introversion/extraversion and empathetic concern are both genetically influenced Moderate heritability (+.40) Nonshared environmental influences are most important

45 Table 2.5 Personality Resemblances among Family Members at Three Levels of Kinship. Sources: Loehlin, 1985, Loehlin & Nichols, 1976.

46 HEREDITARY INFLUENCES ON BEHAVIOR Aspects of Environment Influencing Personality Nonshared environmental influences Differing parental treatment Sibling interaction

47 HEREDITARY INFLUENCES ON BEHAVIOR Hereditary Contributions to Behavior Disorders and Mental Illness Schizophrenia, alcoholism, criminality, depression, hyperactivity, bipolar disorder, neurotic disorders all genetically influenced Inherit a predisposition, not the disorder

48 THEORIES OF HEREDITARY AND ENVIRONMENTAL INTERACTIONS IN DEVELOPMENT Canalization genetic restriction of phenotype to small number of outcomes The Canalization Principle Multiple pathways individuals may develop Nature and nurture combine to determine pathway Either genes or environment may limit the extent the other can influence development

49 THEORIES OF HEREDITARY AND ENVIRONMENTAL INTERACTIONS IN DEVELOPMENT The Range-of-Reaction Principle Genotype sets a range of possible outcomes Environment largely influences where within the range an attribute will fall

50 Figure 2.13 Hypothetical reaction ranges for the intellectual performances of three children in restricted, average, and intellectually-enriching environments. Adapted from Heritability of Personality: A Demonstration, by I. Gottsman, 1963, Psychological Monographs, 11 (Whole No. 572). Copyright 1963 by the American Psychological Association.

51 THEORIES OF HEREDITARY AND ENVIRONMENTAL INTERACTIONS IN DEVELOPMENT Genotype-Environment Correlations Passive home environment is influenced by parents genotypes Evocative genetically influenced attributes affects behavior of others toward the child Active environments children seek will be compatible with genetic predispositions

52 THEORIES OF HEREDITARY AND ENVIRONMENTAL INTERACTIONS IN DEVELOPMENT How Do Genotype-Environment Correlations Influence Development? Passive important when young Evocative remain important throughout development Active important as a child matures

53 Figure 2.14 Relative influence of passive, evocative, and active (niche-picking) genotype/environment correlations as a function of age.

54 CONTRIBUTIONS AND CRITICISMS OF THE BEHAVIORAL GENETICS APPROACH Contributions Many attributes thought to be environmentally determined are influenced by genes Genetics and environment interact Criticisms Describes, does not explain development Environmental forces are unspecified

55 THE ETHOLOGICAL AND EVOLUTIONARY VIEWPOINTS Ethology: scientific study of evolutionary basis of behavior and the contributions of evolved responses to survival and development Assumptions of Classical Ethology: Born with biologically programmed behaviors (through natural selection) Products of evolution Adaptive to survival

56 THE ETHOLOGICAL AND EVOLUTIONARY VIEWPOINTS Assumptions of Ethology Focus on instinctual responses that All members of species share May steer individuals along similar developmental paths Study subjects in natural environment

57 THE ETHOLOGICAL AND EVOLUTIONARY VIEWPOINTS Ethology and Human Development Crying (for example) Ensures infant s basic needs are met Ensures sufficient contact to form primary emotional attachments Critical periods: limited time span when organisms are biologically prepared to display adaptive patterns of development, given right input

58 THE ETHOLOGICAL AND EVOLUTIONARY VIEWPOINTS Ethology and Human Development Sensitive periods: Optimal time for emergence of behaviors Particularly sensitive to environmental influences Development can occur outside a sensitive period, but is more difficult

59 THE ETHOLOGICAL AND EVOLUTIONARY VIEWPOINTS Modern Evolutionary Theory Adaptive motives and behaviors ensure survival and spread of an individual s genes Individual can die if family member survives, as they carry his or her genes

60 THE ETHOLOGICAL AND EVOLUTIONARY VIEWPOINTS Contributions Children have adaptive, genetically preprogrammed characteristics that influence development. Value of studying human development in normal, everyday settings Value of comparing human development with that of other species

61 THE ETHOLOGICAL AND EVOLUTIONARY VIEWPOINTS Criticisms Difficult to test Learning tends to modify most biological predispositions