Transcript Genetics and Behavior Principles of Gene Action and Heredity

The Human Heritage:
Genes and the Environment
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
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
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
Cell Division: Somatic Cells
• Mitosis
– for somatic (body) cells
– each cell replicates itself, then divides
– result is two cells identical to original
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
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
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
Not Exactly Identical
Mendel’s Laws of Inheritance
• Definitions of terms
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locus
homozygous
heterozygous
allele
dominant
recessive
intermediate expression of trait
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
Codominance:
Result is distinct characteristics
Genetic Sex also Source of
Variability
Sex Linked Genetic Effects:
Red/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
Gene-Environment Interactions
• Behavioral geneticists study how genes and
environment combine to influence organism’s
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
Range of Reaction:
charting the change in phenotype as environment changes
Canalization:
some characteristics restricted to narrow range despite wide
variation in environment
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?
Heritability, cont’d
• 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 h2=0
• h2=1- variance accounted for by environment
• heritability increases as genetic diversity
increases and decreases as genetic diversity
decreases
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.
Heritability of Intelligence: History
• Francis Galton’s 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: Darwin’s cousin
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
Intelligence: The Findings
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Identical twins raised apart
Identical twins raised together
Same sex twins raised together
Diff sex twins raised together
Siblings
Unrelated siblings
.72
.86
.62
.57
.47
.30
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
Heritablity of Schizophrenia
• Twin Studies
– High concordance for identical twins, this
concordance deceases as genetic relatedness
decreases
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Identical twins
Fraternal twins
Siblings
Half-sibling
Fisrt cousin
Child of two sch. Parents
Child of one sch. Parent
48% concordance
17%
9%
6%
2%
46%
13%
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)
Chromosomal Errors
• Most incompatible with survival
• Variations in number sex chromosomes
– Turner’s XO
– Klinefelter’s XXY
– XYY
• Variations in number of other chromosomes
– Down’s Syndrome, Trisomy 21
– Edward’s Syndrome; Trisomy 17
PKU
• Recessive gene disorder
• causes excessive buildup of
phenylalaline causing brain damage
• environmental intervention (diet) can
reduce effects
Huntington’s 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
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
Cultural and Survival
• Some cultural tools may ensure survival
– Hunting, gathering methods
– Language
– Child rearing practices (Quechuan babies)
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