1 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Chapter 3 Nature-Nurture

2 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Species Heredity Genetic endowment -Species have in common -Govern maturation and aging processes. Examples in humans -2 eyes, mature sexually at age 12 to 14 Evolved through natural selection -Genes allowing species to adapt passed on

3 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Evolution Charles Darwin ( ) -How characteristics of a species change over time -How new species can evolve from earlier ones Main arguments -There is genetic variation in a species -Some genes aid in adaptation more than others Kettlewell’s moths (1959): Genetic variability allows adaptation

4 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Modern Evolutionary Perspectives How what we do today was adaptive for ancestors. -Ethology: Evolution of behavior in natural environments -Developmental psychobiology: Biology & environment Example: Mothers (~all mammals) invest more than fathers in childrearing - maternity certain -Adaptive mammalian male reproductive strategies -Invest energy in few offspring – paternity certain -Multiple partners/small investment – paternity uncertain

5 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Individual Heredity – The Genetic Code Zygote: Union of sperm and ovum at conception -Contains 23 pairs of chromosomes, one from each parent -Both members of each pair influence same characteristic -Chromosomes: Thousands of genes containing DNA The Human Genome Project: Human genetic code Meiosis: Process producing sperm and ova Mitosis: Cell-division process creating new cells throughout life

6 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Genetic Uniqueness and Relatedness 2 chromosomes in a sperm or ovum during meiosis -64 trillion potential genetically unique babies per couple Identical Twins: A zygote divides forming two genetically identical individuals -Parent and child are 50% genetically related because they share half their genes -Siblings are on average 50% genetically related -Fraternal Twins: Two ova are released and fertilized by two sperm -Males: XY, Females: XX

7 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Translation of the Genetic Code Genes provide instructions for development of various characteristics. -Example: Eye color, or the development of neurons Specific gene pairs turned on or off by regulator genes at different times. -Regulator genes responsible for adolescent growth -Same genes shut down the action in adulthood Genotype: Inherited genetic makeup (genetic potential for tallness) Phenotype: The characteristic/trait expressed (actual height)

8 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Mechanisms of Inheritance Single Gene-Pair Inheritance -Dominant Genes: Dominant trait -Recessive Genes: -Recessive trait if paired with a similar gene -Trait not produced if paired with a dominant gene -Recessive Traits: Homozygous recessive genes. -Dominant Traits: Dominant hetero-or homozygous gene pair

9 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Single Gene-Pair Inheritance: Sickle-Cell Disease About 9% of Americans affected -Homozygous recessive Heterozygous: Carriers -Can transmit gene to offspring -If both parents carriers: 25% chance

10 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Mechanisms of Inheritance: Sex-Linked Inheritance Single genes located on sex chromosomes Actually X-linked Males have no counterpart on Y chromosome Females have counterpart on second X chromosome -Requires gene on both X’s for trait Hemophilia, Colorblindness, Duchene MD

11 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Mechanisms of Inheritance: Polygenic Inheritance Most important human characteristics -Height, weight, intelligence, temperament, personality, sexual orientation, etc. Multiple (100s, 1000s) pairs of genes -~infinite combinations of genes leads to… Normally distribution of these characteristics

12 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Alternative Mechanisms of Inheritance : Mutations A change in structure/arrangement Produces a new phenotype Sperm more likely than ova May be harmful or beneficial -Sickle-cell gene prevents malaria

13 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Chromosome Abnormalities Errors in chromosome division during meiosis -Too many or too few chromosomes Most spontaneously aborted Down Syndrome: Trisomy 21 -Physical deformities -Mental retardation -Related to age of parents

14 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Behavioral Genetics Genetic/environmental cause of traits Heritability estimates (population estimates) -% of variability in characteristic due to genetic var Experimental and selective breeding -Tryon’s maze-bright rats Twin, adoption, family studies -Reared together or apart -Concordance rates

15 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Behavioral Genetics Studies reveal substantial heritability for many physiological, psychological and behavioral traits -MZ correlations higher than DZ correlations -Similar for reared together & apart -Correlations higher for biological relatives than for (adopted) family members

16 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Figure 3.4

17 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Behavioral Genetics DZ correlations typically less than 1.0 Identical twins more alike with age Correlations higher if twins reared together -Suggests that environment also plays a role -Multiple types of environmental influence possible

18 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Estimating Influences Genetic similarity -Degree of genotype similarity Shared environmental influences -Living in the same home, same parents, etc. Non-shared environmental influences -Unique experiences -Youngest v. oldest child, Parental favorite, etc.

19 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Estimating Influences Similar environments & experiences have little impact & do not make us more alike -Shared genes (NOT shared environ) make us similar -Non-shared environment makes us different

20 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Individual Differences in Personality 40% genetic 40% environment (+ 20% error) -Shared: 5% -Non-shared: 35%

21 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Temperament and Personality Temperament correlations -Identical Twins: Fraternal Twins: 0 Personality correlations similar -Shared environment unimportant -Non shared environment and genes important

22 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Nature & Nurture Reciprocal determinism -Heritability < 1.0 revealing environmental influence -Environmental influence interacts w/ genes in development -Genes -> environment -> genes & development -Ex: genetic potential for intelligence interacts w/ enriched environment -Genotype v. phenotype

23 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Figure 3.5

24 of 23 Carol K. Sigelman, Elizabeth A. Rider Life-Span Human Development, 4th Edition Chapter 3: Genes, Environment, and Development Ex: Sociable genes Passive: -Inherited genes + parents create social environment Evocative -Smiley baby gets more social stimulation -Non-shared Active -Sociable child seeks social activities -Non-shared Gene/Environment Interactions (correlations) Passive: -Inherited genes + parents create environ consistent w/ genes Evocative -Genetically influenced temperament evokes different responses Active -Seek experiences consistent with genes