The Human Heritage: Genes and the Environment - PowerPoint PPT Presentation

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The Human Heritage: Genes and the Environment

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Title: The Human Heritage: Genes and the Environment


1
The Human HeritageGenes and the Environment
2
Nature/Nurture
  • First coined by Richard Mulcaster (1582)
  • Refers to the twin forces on development
  • Biological and environmental influences
  • Nature
  • Inborn biological endowment
  • Nurture
  • environment within which development occurs
  • Interaction of Forces

3
Sexual Reproduction and Genetic Transmission
  • Chromosomes
  • Single molecule of DNA, thousands of genes
  • 23 23 zygote
  • Genes
  • segments of DNA, double helix, ladderlike
  • blueprint for synthesis of protein molecule
  • units of heredity

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5
Sexual Reproduction and Patterns of Heredity
  • The basics
  • somatic cells hold genetic info on copies of 46
    chromosomes inherited at conception
  • Chromosomes dispersed throughout the nucleus
  • 23 pairs of chromosomes
  • 22 autosomes, 1 sex chromosome
  • males xy
  • females xx

6
Cell Division Somatic Cells
  • Mitosis
  • for somatic (body) cells
  • each cell replicates itself, then divides
  • result is two cells identical to original

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Cell Division Germ Cells
  • Meiosis
  • for germ cells
  • replication with 3 processes to ensure resulting
    cell is nonidentical to germ cells (genetic
    diversity chances are 1/70 trillion)
  • 2 steps of division
  • crossing over
  • random pairing during 2nd division
  • monozygotic vs. dizygotic twins

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10
Genotype/Phenotype
  • Genotype
  • the set of genes you inherit, your unique
    blueprint
  • Phenotype
  • how that set of genes is expressed as a result of
    the environmental stresses
  • the observable characteristics

11
Environment
  • Genetic code is expressed in environments
  • Multi-levels of influence possible (egs.)
  • prenatal hormonal environment
  • chemical environment of the cell
  • nutrition of mother during pregnancy
  • stress of mother
  • opportunity for physical exercise
  • birth order as it relates to attention from parent

12
Not Exactly Identical
13
Mendels Laws of Inheritance
  • Definitions of terms
  • locus
  • homozygous
  • heterozygous
  • allele
  • dominant
  • recessive
  • intermediate expression of trait

14
Laws of Inheritance
  • Discrete traits inherited on the basis of allele
    information from a single locus
  • Chin cleft
  • Blood type
  • Polygenetic traits inherited as result of
    information from several genes
  • Verbal skill
  • shyness

15
Codominance Result is distinct characteristics
16
Genetic Sex also Source of Variability
17
Sex Linked Genetic EffectsRed/Green
Colorblindness
  • recessive trait
  • chances are 1/10 for males
  • chances are 1/100 for females
  • gene carried on x chrom, males have no
    complementary allele to compensate for the
    harmful effects

18
Gene-Environment Interactions
  • Behavioral geneticists study how genes and
    environment combine to influence organisms
    development
  • Variations in environment can have large effects
    on development of phenotype
  • Gene-environment interaction is a two-way process
  • Genetic factors play a role in the environments
    that individuals inhabit and how they shape their
    environments

19
Range of Reaction charting the change in
phenotype as environment changes
20
Canalization some characteristics restricted to
narrow range despite wide variation in environment
21
Heritability The study of genetic influences on
behavior
  • Attempt to assess the degree to which variation
    among individuals on a given trait can be
    attributed to genetic as compared to
    environmental differences
  • e.g., weight - a physical trait
  • e.g., intelligence - a psychological trait
  • can factors in the environment influence weight
    or intelligence?

22
Heritability, contd
  • Degree to which variation among individuals on a
    particular trait can be attributed to genetic
    differences
  • h2 variation due to genes
  • total variation
  • applies to groups and not to individuals
  • for clones, any variation has to be due to
    environment, thus h20
  • h21- variance accounted for by environment
  • heritability increases as genetic diversity
    increases and decreases as genetic diversity
    decreases

23
Heritability Infant Temperament
  • This video from the laboratory of Hill Goldsmith
    shows part of a study about infant temperament.
    An object of desire is set in motion, first for
    each infant in a pair of fraternal twins and then
    for each infant in a pair of identical twins.
    Note how the twins react when prevented from
    reaching the desired object.

24
Heritability of Intelligence History
  • Francis Galtons Eminent Persons Study
  • tested idea that differences in intellectual
    achievement was due to genetic differences
  • basic flaw in logic is that eminent people also
    shared similar environment as well as gene pool
  • first to use adoptive method in study of boys
    adopted by RC Popes found little evidence that
    environment affected eminence
  • Recommendations made for selective breeding, as
    they were to be made later by Hitler
  • Interesting aside Darwins cousin

25
Heritability of Intelligence Kinship Studies
  • Twin Methods
  • correlations among IQs of pairs of people related
    to different degrees, e.g., identical twins,
    dizygotic twins, siblings,
  • Adoptive Methods
  • correlations among pairs of people who share an
    environment but not genes, e.g., adopted child
    and biological child

26
Intelligence The Findings
  • Identical twins raised apart .72
  • Identical twins raised together .86
  • Same sex twins raised together .62
  • Diff sex twins raised together .57
  • Siblings .47
  • Unrelated siblings .30

27
Heritability of Schizophrenia
  • Adoption Studies
  • e.g., Kety et al (1976) found strong evidence of
    heritability
  • only biological relatives of adoptee who is
    schizophrenic show high incidence of schizophrenia

28
Heritablity of Schizophrenia
  • Twin Studies
  • High concordance for identical twins, this
    concordance deceases as genetic relatedness
    decreases
  • Identical twins 48 concordance
  • Fraternal twins 17
  • Siblings 9
  • Half-sibling 6
  • Fisrt cousin 2
  • Child of two sch. Parents 46
  • Child of one sch. Parent 13

29
Mutations and Genetic Abnormalities
  • Mutations are errors in the process of gene
    replication can be positive but usually negative
  • Down Syndrome (chromosomal error)
  • Phenylketonuria (PKU- defective recessive gene)
  • Klinefelter syndrome (sex-linked chromosomal
    abnormality)
  • Sickle-cell anemia (recessive gene)

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31
Chromosomal Errors
  • Most incompatible with survival
  • Variations in number sex chromosomes
  • Turners XO
  • Klinefelters XXY
  • XYY
  • Variations in number of other chromosomes
  • Downs Syndrome, Trisomy 21
  • Edwards Syndrome Trisomy 17

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33
PKU
  • Recessive gene disorder
  • causes excessive buildup of phenylalaline
    causing brain damage
  • environmental intervention (diet) can reduce
    effects

34
Huntingtons Disease
  • dominant gene disorder
  • 50 chance of offspring inherit the disorder
  • 1/15,000 incidence
  • charcterized by severe mental and physical
    disorder
  • lag in onset of symptoms (35-45 yrs) accounts for
    continued occurrence
  • can be detected through genetic testing

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36
Biology and Culture
  • Cultural evolution can also account for existence
    of skills in a population
  • Innovations passed onto succeeding generations
  • Through processes of direct instruction,
    language, and demonstration
  • Little evidence of cultural evolution in other
    species
  • Meme basic unit of cultural evolution

37
Cultural and Survival
  • Some cultural tools may ensure survival
  • Hunting, gathering methods
  • Language
  • Child rearing practices (Quechuan babies)

38
Coevolution
  • Two forms of evolution (cultural and biological)
    influence each other
  • Evidence that culture has influenced biology
    through the impact it has on reproductive
    advantage (e.g., tool use)
  • The problems of sorting out the nature-nurture
    influence

39
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