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CHAPTER 3 GENES, ENVIRONMENT AND DEVELOPMENT

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Title: SR6e Chapter 3 Author: Suzanne Krinsky Last modified by: Julie B. Hanauer Created Date: 9/13/2004 11:16:45 PM Document presentation format – PowerPoint PPT presentation

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Title: CHAPTER 3 GENES, ENVIRONMENT AND DEVELOPMENT


1
CHAPTER 3 GENES, ENVIRONMENT AND DEVELOPMENT
2
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

3
Individual Heredity The Genetic Code
  • Meiosis process producing sperm, ova
  • Mitosis cell-division process creating all other
    cells throughout life

4
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

5
Genetic Uniqueness and Relatedness
  • Monozygotic (MZ) twins 100 related
  • Single zygote divides
  • 2 genetically identical individuals
  • Dizygotic (DZ) twins 50 on average
  • 2 ova fertilized by 2 sperm
  • Siblings 50 on average
  • Parent Child 50 related, shared
  • Males XY Females XX

6
Translation of the Genetic Code
  • Genes instructions for development
  • Characteristics like eye color, height, IQ
  • Genotype genetic makeup a person inherits
    (potential) e.g., genes for tallness
  • Phenotype actual/expressed trait (height)
  • 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

7
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

8
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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10
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

11
  • X-Linked Inheritance

12
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

13
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

14
Chromosomal Abnormalities
  • Errors in chromosome division during meiosis
  • Too many or too few chromosomes result
  • Most spontaneously aborted

15
Chromosomal Abnormalities
  • Down Syndrome Trisomy 21
  • Physical characteristics
  • Mental retardation
  • Related to age of both parents
  • Often develop Alzheimers in middle age

16
  • The rate of Down syndrome births increases
    steeply as the mothers age increases.

17
Sex chromosome Abnormalities
  • Turners syndrome 1/3000 females
  • Single X chromosome (XO) small, unable to
    reproduce, stubby fingers, webbed neck

18
Sex chromosome Abnormalities
  • Klinefelter syndrome 1/200 males
  • XXY Sterility, feminine traits

19
Sex chromosome Abnormalities
  • Fragile X syndrome one arm on X is fragile (Leg
    of X barely connected)
  • Usually males (sex-linked inheritance)
  • Most common heredity cause of MR

20
Genetic Diagnosis and Counseling
  • Helps people understand and adapt
  • Prenatal diagnosis techniques include
  • Amniocentisis, preimplantation
  • Human genome project yielded much info

21
Genetic Diagnosis and Counseling
  • Tay-Sachs disease
  • Cause recessive gene pair (European Jews/French
    Canadians)
  • Huntingtons disease
  • Deterioration of nervous system
  • Single dominant gene
  • One affected parent 50 chance in offspring

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23
Behavioral Genetics
  • Genetic/environmental cause of traits
  • Heritibility estimates proportion of phenotypic
    variation in a population that is attributable to
    genetic variation among individuals.
  • Experimental and selective breeding
  • Tryons maze-bright rats
  • Twin, adoption, family studies
  • Reared together or apart
  • Concordance rates--twins are concordant if they
    both display a trait of interest

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25
Estimating Influences
  • Genetic similarity
  • Degree of trait similarity
  • Shared environmental influence
  • Living in the same home
  • Non-shared environmental influences
  • Unique experiences
  • Genetic similarity
  • Degree of trait similarity
  • Shared environmental influence
  • Living in the same home
  • Non-shared environmental influences
  • Unique experiences
  • Genetic similarity
  • Degree of trait similarity
  • Shared environmental influence
  • Living in the same home
  • Non-shared environmental influences
  • Unique experiences

26
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

27
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

28
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29
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

30
  • Correlations between the traits of identical
    twins raised apart in Minnesota Twin Study.

31
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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