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Biological Bases of Behaviour.
Lecture 2: Genetics and Behaviour.
Learning Outcomes.
 At the end of this lecture you should be able to:
 1. Describe what is meant by 'genetics'.
 2. Outline (using appropriate examples) the laws of genetic
inheritance.
 3. Describe the ways in which genes influence human
development and behaviour.
 4. Explain, using experimental examples, what is meant by
'heritability'.
Genetics.
 Genetics has been defined as " the study of the structure
and function of genes and the way in which genes are
passed from one generation to another" (Russell, 1992).
 How do genes affect behaviour?
 1. Genes determine how amino acids construct proteins and
enzymes which then form the cells of the body and nervous
system.
 2. Genes interact with their immediate physical
environment and control the development of the foetus.
 3. Behaviour is determined by the nervous system
interacting with its environment.
 Carlson et al., (1997): it is incorrect to speak of particular
genes for specific behaviours. There are only genes for
determining the physical structures and physiological
processes that underlie behaviour.
Laws of Genetic Inheritance.
 Before the 1860's, it was thought that acquired
characteristics could be inherited (e.g. a blacksmith with a
strong right arm may have a son with a strong right arm).
 This was called 'Lamarckism' after its proposer JeanBaptiste Lamarck.
 Darwin called this 'pangenesis’ but realised it had a key
problem, (e.g. circumcision is not inherited). He argued
that all units of the body produce 'gemmules' which can be
passed on to the next generation.
 Inheritance was seen as a photocopier producing an exact
copy each time (aside from mutations).
 However, children are not an exact copy of their parents,
some features are identifiable as coming from one parent
but others appear to be blends of both parents.
The Father of Genetics.
 In carefully conducted breeding experiments
with peas, Mendel found that if he crossed a
plant with purple flowers with one that
produced white flowers, the offspring would
all be purple.
 However, if these purple offspring were then
bred with one another, their offspring would
show the pattern of one with white flowers
to 3 with purple flowers.
 He realised that certain characteristics were
inherited on an all-or-nothing basis, and that
blending was not taking place.
 He established that inheritance occurs in a
predictable way, and that certain traits are
passed down through the generations (not
always being expressed however).
Gregor
Mendel
Mendelian Genetics.
 In the simplest form of hereditary transmission, a single
pair of genes, one from each parent, determines a
particular inherited characteristic.
 Genes that control a particular trait can have alternative
forms called alleles; e.g. the gene that controls blood type
has three alleles A, B, and O.
 When the corresponding genes inherited from the parents
are the same, then the individual is 'homozygous' for the
trait. They will express that characteristic.
 When the alleles are different, the individual is said to be
'heterozygous'. There are then one of three outcomes :
Outcomes of Heterozygosity
 1. They will display the characteristic described by the
dominant allele, a characteristic from a recessive allele is
not expressed (e.g. blue eyes).
 2. The offspring will show the effects of both alleles and
will display a characteristic that is intermediate between
those of offspring who are homozygous for either allele.
E.g. skin colour.
 3. The offspring will display a characteristic that is
contributed to by both alleles, but rather than being
intermediate, it is distinctly different from that specified by
either allele, this is called co-dominance.
 E.g. a parent with type A blood and a parent with type B
blood will produce an offspring with type AB blood which is
different from either A or B types.
Mendelian Inheritance.
Badcock, (2000), p47
Chromosomes.
 The 80-100,000 genes found in each cell nucleus of the human body
are housed in 46 chromosomes (23 pairs).
Sex Chromosomes.
 Humans possess 44
'autosomal chromosomes',
and 2 'sex-linked
chromosomes’, designated
as X and Y.
 Females possess 2 X's
while males posses an X
and a Y.
 The X chromosome carries
many genes, but the Y
chromosome only carries a
few genes that ensure the
developing male foetus
becomes ‘male’.
Carlson et al., (2000), p74
Sex Chromosome-Linked Disorders.
 Because females receive two X chromosomes they get two
doses of sex-linked genes, but males only receive one dose,
which always comes from the mother.
 This asymmetry leaves males susceptible to a number of
genetic defects that do not affect females.
 This is because if a female has a harmful recessive gene on
one chromosome, she usually has a dominant 'normal' gene
on the other chromosome to counteract it, so the recessive
gene is not expressed.
Examples of Sex-Linked Genetic
Disorders.
 1. Colour Blindness: Red/green colour blindness is rare in
females as they would need both their father and mother to
carry the gene. It is fairly common in men as they only
need a mother to carry the gene.
 2. Haemophilia: This blood clotting disorder was common in
the European Royal families. The originator was Queen
Victoria who carried a recessive gene on one of her X
chromosomes.
 She and all her female descendants did not show the
disease because the defective gene was paired with a
dominant non-defective gene.
 Her male descendants who inherited the defective X
chromosome suffered from the disease, and passed it on to
their daughters, who in turn then passed it down to their
sons.
DNA
(Deoxoribonucleic acid).
 Crick & Watson (1953) showed that DNA consisted of 2
helical spirals linked by 4 chemical bases (adenine,
cytosine, guanine and thymine).
 These chemical bases are linked in a particular fashion (A
with T; G with C).
 Genetic information is copied and transmitted when the
strands separate and join with new complementary bases.
 The genetic code is written in triplets of DNA bases.
 The triplet sequence describes the types of proteins that
will be synthesised, and how they will become assembled.
 The total complement of human DNA (genome) consists of
individual genes, thousands or millions of base-pairs long
DNA Structure.
From Genes to Behaviour.
 Epigenesis describes the study of the ways in which genes
bring about their effects on growth and development.
 Badcock (2000): it is wrong to think of genes as forming a
'blueprint' for the body and mind as genes do not specify
every detail of an individual.
 Genes initiate a particular developmental pattern that is
then left free to run in the face of many possible
environmental and physiological changes.
 In order to determine the relative contributions made by
genes or the environment we need to distinguish between:
 Genotype: particular alleles inherited by the individual.
 Phenotype: observable characteristics that develop through
interactions between the genotype and the environment.
Gene / Environment Interactions.
Environment
Developmental
history
Genes
Proteins
Adapted from Toates, (2001), p34
Structure
of nervous
system
stimuli
Behaviour
Genotype/Phenotype Interactions
 E.g Siamese cats have dark fur on their tails, paws and ears;
this raises the following questions:
 Is there a gene for colouring the corners of a cat?
 If such a gene exists, how does it 'know' where the 'corners'
are, and how to colour them?
 Siamese cats have a gene for producing an enzyme
responsible for coloration, but is only expressed at certain
temperatures. As the extremities are cooler, the gene is
expressed and they become dark.
 For complex human behaviours it is nearly impossible to
isolate genetic from environmental variables.
Genetic Influence.
 Determining genetic influence on the phenotype is complicated by
the fact that many traits are polygenic. Modifier genes can also alter
the actions of other genes. E.g. there are two alleles for eye colour
(blue and brown) but eyes are not always blue or brown. Genes give
a probabilistic bias towards a certain behaviour emerging (or not) in
the face of a particular environmental influence occurring (or not).
good soil
Toates (2001), p34
poor soil
Types of Genetic Determination.
 According to Cartwright (2000) there exists a spectrum in
the 'genetic determination' of behaviour:
 1. Innate behaviours displayed irrespective of environment
(e.g. male sticklebacks attack anything red in any
situation).
 2. Innate behaviours modified by learning (e.g. pecking
behaviour in chicks becomes more discriminating through
experience).
 3. Selectively learnt, or expressed (e.g. Male chaffinches
pick out characteristic sounds of their own species when
learning to sing).
 4. Learnt behaviour (e.g. blue tits peeling back milk bottle
tops). Much of human behaviour falls into this category, it
is unlikely that there are genes for playing the violin.
Heredity and Behaviour Genetics.
 Kalat (2001): people ask 'which is more important, heredity or
environment?' This is impossible to answer as no behaviour
can develop without both.
 The following is more meaningful: 'do the observed
differences among individuals depend more on differences in
heredity or differences in environment?'
 The degree to which differences in a characteristic are due to
genetic differences is called heritability.
 This always takes a value between 0 and 1: eye colour has a
heritability of 1, i.e. the environment plays no role.
 The scientific study of heritability (the effects of genes on
behaviour) is called behaviour genetics.
 There are several methods in behaviour genetics:
1. Artificial Selection.
 E.g. Tryon (1940) trained rats to find their way through a maze.
He selectively bred the 'fastest' and the 'slowest'. Over many
generations two clear groups emerged:
Carlson et al., (2000), p 81
2. Family Studies.
 We can take a specific family member (proband) and
compare their behaviours with people of differing genetic
relatedness.
 If a characteristic is more common in closely related
individuals then we may conclude that it has a genetic
component.
 However, family members are typically raised in similar
environments.
 Some studies have compared identical (monozygotic or MZ)
twins with non-identical (dizygotic or DZ ) twins.
 Because MZ twins are genetically identical they should
show greater similarities (concordance) in their behaviours
than non-identical twins.
Concordance Studies.
 Some studies have shown that MZ twins show high concordance
for many physical and behavioural characteristics.
Vasta et al., (1999), p 106.
Behaviours Across the Life-Span.
 Plomin & DeFries (1998) showed that verbal ability and spatial
ability remained highly correlated between MZ twins.
Carlson et al., (2000), p371
Identical Twins Raised Apart.
 Twins are reared in the same environments, and are often
dressed in the same way, parents expect them to behave in
the same way.
 Such expectations can influence how they do behave.
 If genes play a role in certain behaviours then identical
twins raised apart should still be more similar than nonidentical twins raised apart.
 The best know study of this type was the 'Minnesota Study
of Twins Reared Apart' (Bouchard et al., 1990).
 This study did indeed reveal that MZ twins showed greater
similarities than DZ twins even when reared apart.
 However, in many cases the twins were reared with
relatives.
References and Bibliography.
 Badcock, C. (2000). Evolutionary Psychology: a Critical Introduction.
Polity Press.
 Bouchard, T.J.Jnr., Lykken, D.T., McGue, M., Segal, N.L., & Tellegen, A.
(1990). Sources of human psychological differences: the Minnesota
Study of Twins Reared Apart. Science, 250: 223-228.
 Carlson, N.R., Buskist, W., & Martin, G.N. (1997). Psychology the
Science of Behaviour. Allyn & Bacon.
 Cartwright, J. (2000). Evolution and Human Behaviour, Macmillan
Press, chapter 3.
 Henin, R.M. (2000). A Monk and Two Peas. Phoenix.
 Kalat, J.W. (2001). Biological Psychology. Wadsworth.
 Plomin, R., & DeFries, J.C. (1998). The genetics of cognitive abilities
and disabilities. Scientific American, 278: 40-47.
References continued.
 Plomin, R., & Rutter, M. (1998). Child development, molecular
genetics and what to do with genes once they are found. Child
Development, 69: 1223-1242.
 Russell, P.J. (1992). Genetics. Harper Collins.
 Toates, F. (2000). Biological Psychology: an Integrative Approach.
Prentice Hall.
 Tryon, R. (1940). Genetic differences in maze-learning ability in
rats. Yearbook of the National Society for the Study of Education,
39: 111-119.
 Vasta, R., Haith, M.M., & Miller, S.A. (1999). Child Psychology: the
Modern Science. John Wiley & Sons.