CHAPTER 3 GENES, ENVIRONMENT AND DEVELOPMENT

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CHAPTER 3GENES, ENVIRONMENT AND DEVELOPMENT
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Learning Objective

• What do evolution and species heredity contribute
  to our understanding of universal patterns of
  development?

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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

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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

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Kettlewells Moths

• An interaction
• Genetic variability (color of wings)
• Adaptation to a specific environment (country
  vs.city)
• Survival
• Requires adaptation
• Adaptation
• Genetic variability

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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

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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.

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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

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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

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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

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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

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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?

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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

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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

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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

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• X-Linked Inheritance

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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

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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?

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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

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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 Alzheimers in middle age

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• The rate of Down syndrome births increases
  steeply as the mothers age increases.

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Sex chromosome Abnormalities

• Turners 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

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Genetic Diagnosis and Counseling

• Helps people understand and adapt
• Prenatal diagnosis techniques include
• Amniocentisis, preimplantation genetic diagnosis
• Human genome project yielded much info
• Eg., Huntingtons disease
• Deterioration of nervous system
• Single dominant gene
• One affected parent 50 chance in offspring

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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?

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Behavioral Genetics

• Genetic/environmental cause of traits
• Heritibility estimates
• Experimental and selective breeding
• Tryons maze-bright rats
• Twin, adoption, family studies
• Reared together or apart
• Concordance rates

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Estimating Influences

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

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Molecular Genetics

• Analysis of genes and their effects
• May compare humans with other animals
• Eg. Alzheimers 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

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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?

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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

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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

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

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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

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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?

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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