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 –What species members have in common –Govern maturation and aging processes Examples in humans –Two eyes, sexually mature at ages Evolved through natural selection –Genes passed on which allow species to adapt

Evolution Evolution: Charles Darwin ( ) –Specie characteristics change over time –New species can evolve from earlier ones Main arguments –There is genetic variation in a species –Natural selection Adaptive genes passed on more frequently

Kettlewell’s Moths An interaction –Genetic variability (color of wings) –Adaptation to a specific environment (country vs.city) Survival –Requires adaptation Adaptation –Genetic variability

Modern Evolutionary Perspectives What we do today was adaptive for our ancestors Species heredity based on natural selection Genetic make-up gradually changes New or modified species arise Cultural evolution based on learning –Better ways of adapting learned –Shared through language

Learning Objectives What are the basic workings of individual heredity, including the contributions of genes, chromosomes, the zygote, and the processes of mitosis and meiosis? Note the difference between genotype and phenotype.

Individual Heredity – The Genetic Code Zygote: Union of sperm & ovum at conception –Contains 23 pairs of chromosomes One pair from each parent Each pair influences a characteristic Chromosomes: thousands of genes containing DNA Meiosis: process producing sperm, ova Mitosis: cell-division process creating all other cells –Throughout life

The Human Genome Project Massive genome analysis projects 999/1000 human base chemicals: identical 1/1000 accounts for differences between us Humans/Chimps share 96% genetic material Gene variants evolved in recent centuries –Adaptations to food sources, diseases,etc. Findings also useful to identify genes associated with disease, drug treatments

Genetic Uniqueness and Relatedness ID twins: zygote divides forms 2 individuals 64 trillion genetically unique babies per any couple –2 chromosomes in sperm or ovum –Males: XY, Females: XX Parent/Child: 50% related genetically Siblings: on average 50% related genetically Fraternal twins: 2 ova released, fertilized by 2 sperm

Translation of the Genetic Code Genotype: genetic makeup a person inherits Phenotype: expressed traits of the person Genes: instructions for development –Characteristics like eye color Regulator genes turn gene pairs on/off at different times –Turned on for adolescent growth spurt –Turned off in adulthood Always influenced by environmental factors also

Learning Objectives How are traits passed from parents to offspring? What is an example of how a child could inherit a trait through each of the three mechanisms described in the text?

Mechanisms of Inheritance Single gene-pair inheritance –Dominant gene = dominant trait –Recessive genes Trait expressed if paired with a similar gene (Homozygous) Trait not expressed if paired with dissimilar gene (Heterozygous) –Recessive traits: homozygous recessive –Dominant traits: hetero or homozygous gene pair

Example: Sickle-Cell Disease About 9% affected in US –Homozygous recessive Heterozygous are “carriers” –Can transmit gene to offspring –If both parents carriers: 25% chance Example of incomplete dominance –Offspring may have sickling episodes

Sex-Linked Inheritance Single genes located on sex chromosomes Actually X-linked Males - no counterpart on Y chromosome –Only needs one to be color-blind Females - counterpart on 2 nd X chromosome –Usually for normal color-vision (dominant) –Must inherit on both to be color-blind Also Hemophilia, Duchene MS, others

X-Linked Inheritance

Polygenic Inheritance For most important human characteristics –Height, intelligence, temperament, etc. Trait influenced by multiple pairs of genes These traits are normally distributed –I.e., found in the same proportion in all populations

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?

Mutations A change in gene structure/arrangement Produces a new phenotype More likely in sperm than in ova May be harmful or beneficial Can be inherited by offspring

Chromosomal Abnormalities Errors in chromosome division during meiosis –Too many or too few chromosomes result –Most spontaneously aborted Down Syndrome: Trisomy 21 –Physical characteristics –Mental retardation –Related to age of both parents –Often develop Alzheimer’s in middle age

The rate of Down syndrome births increases steeply as the mother’s age increases.

Sex chromosome Abnormalities Turner’s syndrome: 1/3000 females –Single X chromosome: small, unable to reproduce Klinefelter syndrome: 1/200 males –XXY: Sterility, feminine traits Fragile X syndrome: one arm on X is fragile –Usually males (sex-linked inheritance) –Most common heredity cause of MR

Genetic Diagnosis and Counseling Helps people understand and adapt Prenatal diagnosis: techniques include –Amniocentisis, preimplantation genetic diagnosis Human genome project yielded much info Eg., Huntington’s disease –Deterioration of nervous system –Single dominant gene –One affected parent = 50% chance in offspring

Learning Objectives How do scientists study the contributions of heredity and environment to behavioral characteristics? Describe the logic of the methods, as well as strengths and weaknesses of each method How can concordance rates help researchers estimate the influences of heredity and environment? How do genes, shared environment, and nonshared environment contribute to individual differences in traits?

Behavioral Genetics Genetic/environmental cause of traits Heritibility estimates Experimental and selective breeding –Tryon’s maze-bright rats Twin, adoption, family studies –Reared together or apart –Concordance rates

Estimating Influences Genetic similarity –Degree of trait similarity Shared environmental influence –Living in the same home Non-shared environmental influences –Unique experiences

Molecular Genetics Analysis of genes and their effects –May compare humans with other animals Eg. Alzheimer’s disease –Most common form of old age dementia –Twin studies show heritability –Possible genetic links being tested –Environmental factors also being tested High cholesterol, head injury

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 heritibility of traits? Which traits are more strongly heritable than others?

IQ: Accounting for Individual Differences Correlations highest in identical twins –Genetic factors determine trait Correlations higher if twins reared together –Environmental factors –Non-shared experiences influential Identical twins more alike with age

Temperament & Personality Temperament Correlations –Identical twins =.50 to.60 –Fraternal twins = 0 (even reared together!) Personality Correlations Similar –Shared environment unimportant –Genetic inheritance important –Non-shared experiences important for differences

Correlations between the traits of identical twins raised apart in Minnesota Twin Study.

Psychological Disorders Schizophrenia concordance rates –ID twins: 48% –Fraternal twins: 17% –Affected parent increases risk even if adopted at birth Inherited predisposition –Environmental factors (triggers) –Prenatal exposure to infection suspected

Learning Objectives What is an example that illustrates the concept of a gene-environment interaction? What are three ways that genes and environments correlate to influence behavior? What are the major controversies surrounding genetic research?

Gene-Environment Interactions Based on correlations Eg., Sociable genes –Passive interaction Create social home environment –Evocative interaction Smiley baby gets more social stimulation –Active interaction Shy child seeks solitary activities