Genetics
The Nature/Nurture Debate
How great is the influence of
genes or environment on our
behavior, personality, biology,
etc.?
The Nature Nurture Debate
Make two columns on a sheet
of paper - 1) nature; 2) nurture
Write characteristics you
believe are mostly nature or
mostly nurture in the
appropriate column
If the characteristic was
nurture, what seemed to be
the influences?
The Simple View
Behavior = genes + environment
The Realistic View
Behavior = genes + prenatal
environment + parental influence
+ nutrition + family income +
education + culture + traumas +
chance …
Genetics and
Behavior
Nucleus
Cell
Chromosome
Gene
DNA
Genotype & Phenotype
Genes: Essential
Definitions
Chromosomes
– threadlike structures made of DNA that
contain the genes
DNA (deoxyribonucleic acid)
– complex molecule containing the
genetic information that makes up the
chromosomes
– has two strands-forming a “double
helix”- held together by bonds between
pairs of nucleotides
Genes: Essential
Definitions
Genes
– biochemical units of heredity that make up
the chromosomes
– a segment of DNA capable of synthesizing a
protein
– The paradox 30,000 genes for 300,000
proteins
Genome
– the complete instructions for making an
organism
– consisting of all the genetic material in its
chromosomes
Genes: Essential
Definitions
Genotype
-The genetic constitution of an individual.
Depending on context, this may refer to
the alleles at a single locus or to the
complete set of genes.
Phenotype
-Any measurable trait of an individual.
Phenotype results from an interaction
between genotype and environment.
Genotypic Variation Is Created
by Sexual Reproduction
What determines the genetic uniqueness
of individuals?
– Gametes
– Zygote
Mutations are experiments in selective
advantage
– Industrial melanism
– Sickle-cell disease
Sickle Cell Disease and
Malaria
- homozygotes
- anemia, joint pain, swollen
spleen, frequent severe infections,
high rate of childhood death
- heterozygotes
- basically normal blood function
- resistant to malaria
Price for malarial resistance
- homozygous sickle cell children
Sexual Reproduction
Combines gametes thereby creating
new genotype
May have evolved to outcompete
parasites
Genes Affect Behavior
Behavioral Genetics Methods:
– Twin Studies Compare MZ and DZ Twins:
– Adoption Studies:
Behavior Genetics
Identical
twins
Fraternal
twins
Identical Twins
– develop from a single
zygote (fertilized egg)
that splits in two,
creating two genetic
replicas
Fraternal Twins
Same
sex only
Same or
opposite sex
– develop from separate
zygotes
– genetically no closer
than brothers and
sisters, but they share
the fetal environment
Nature v Nurture: Twin Studies
Identical (monozygotic twins)
Non-identical, fraternal (dizygotic twins)
Identical twins reared together
same genes (relatedness of 1.0)
same environment
Identical twins reared apart
sane genes (relatedness of 1.0)
different environment
Fraternal twins reared together
half genes the same (relatedness 0.5)
same environment
Fraternal twins reared apart
half genes the same (relatedness 0.5)
different environment
Nature v Nurture: Twin Studies
Jack Yufe:
raised by
Jewish father
in Caribbean
Oskar Stoh
raised by catholi
grandmother i
Nazi German
If we had identical twins reared apart could we separate the effects of
phenotype, of genotype, and of the environment. In some cases this has
happened.
Nature v Nurture: Twin Studies
Both like sweet liqueurs
Store rubber bands on their wrists
Read magazines from back to front
Dip buttered toast in their coffee
Have very similar personalities
MZ and DZ concordance
rates
Separated Twins
Twins Studies
Comparing identical twins
separated at birth
Twins studies movie
Environmental Influences
Prenatal environment
Social and Environmental
Contexts Influence Genetic
Expression
African Americans and
Hypertension: a controversial
theory
Gene expression as concerns child
maltreatment and criminality is
reflected in next slide.
Child Maltreatment, Criminality,
and Gene Expression
Temperament and genetics
Suomi genetic studies on
rhesus monkeys
– Two alleles of one gene:
the “short” version causes
neurobehavioral deficits ONLY IF
the infant monkey is raised with
peers but without its mother
The “long” version causes no
neurobehavioral deficits,
regardless of rearing
– Maternal buffering?
Behavior Genetics
Adoption studies
– Are adopted kids more like their
biological relatives or their
adopted relatives?
– General findings: adoptees more
like biological parents than
adopted parents in intelligence
and personality/temperament