life span 3
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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
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