Life Span 3

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 12-14

• Evolved through natural selection– Genes passed on which allow species to

adapt

Evolution

• Evolution: Charles Darwin (1809-1882)– 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 2nd 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