The Human Heritage: Genes and the Environment

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The Human HeritageGenes and the Environment
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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

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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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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

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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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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

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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

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Not Exactly Identical
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Mendels Laws of Inheritance

• Definitions of terms
• locus
• homozygous
• heterozygous
• allele
• dominant
• recessive
• intermediate expression of trait

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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

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Codominance Result is distinct characteristics
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Genetic Sex also Source of Variability
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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

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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

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Range of Reaction charting the change in
phenotype as environment changes
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Canalization some characteristics restricted to
narrow range despite wide variation in environment
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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?

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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

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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.

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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

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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

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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

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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

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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

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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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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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PKU

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

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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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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

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Cultural and Survival

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

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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

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