Transcript SR6e Chapter 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
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– 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)
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– 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
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– 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
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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
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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
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– 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
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– 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
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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
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– 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
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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
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– 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
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– 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
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X-Linked Inheritance
Polygenic Inheritance
• For most important human characteristics
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– 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
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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
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– 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
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The rate of Down syndrome births increases steeply as the mother’s age increases.
Sex chromosome Abnormalities
• Turner’s syndrome: 1/3000 females
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– 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
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– 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
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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
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– Tryon’s maze-bright rats
Twin, adoption, family studies
– Reared together or apart
– Concordance rates
Estimating Influences
• Genetic similarity
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– 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
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– 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
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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
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– 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
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– 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
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Correlations between the traits of identical twins raised apart in Minnesota Twin Study.
Psychological Disorders
• Schizophrenia concordance rates
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– 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
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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