• Next session: studying heritability
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– Reading
– Preparation Qs
Cars kill many more people than spiders. So
why are phobias of spiders much more
common than phobias of cars?
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Evolution
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Evolution of phobia
Evolution of phobia
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Evolution of phobia
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Evolution of phobia
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Evolution of phobia
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Evolution of phobia
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Evolution of phobia
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X
X
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Today you will…
Learn how to
• Describe biological
structures
• Distinguish between
biological and psychological
concepts
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Learn about
• The role and influence of
genes in humans
•
•
•
•
•
•
•
Gene
Genetics
Heredity
Genotype
Phenotype
Dominant gene
Recessive gene
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How many can you define?
What are genes?
• Genes are bits of DNA which make proteins
– These proteins cause physiological responses in
the body
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• An organism’s genes convey information
about how to construct that organism from
one generation to the next
Genetics and heredity
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• Genetics is the study of how genes influence
physical and behavioural characteristics
• Heredity refers to the traits, tendencies and
characteristics inherited from our
parents/ancestors
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• What’s the difference between genotype and
phenotype?
Genotype vs Phenotype
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• Genotype: the whole set of genetic information
carried by the organism
• Phenotype: the physical manifestation of the
genotype. Only some genes carried in the
genotype will be expressed in the phenotype.
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• Why might a characteristic encoded in the
genotype not be expressed in the phenotype?
• How does this example illustrate the concepts
of phenotype and genotype?
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– John and Alan are identical twins who were
separated at birth. Alan was raised in a very
impoverished environment. John is substantially
taller than Alan.
Remember...
• Just because it’s in the genotype that doesn’t
necessarily mean it’ll be expressed in the
phenotype:
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– The environment influences gene expression
– Some genes are recessive and some are dominant
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• What’s the difference between a dominant
and a recessive gene?
– Dominant genes are always expressed
– Recessive genes are expressed only in the absence
of a dominant gene
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• Genes are organised in chromosomes, these
come in pairs – you inherit one half of each
pair from each parent
Which genes are expressed?
• Consider eye colour:
B = brown eyes (dominant)
b = blue eyes (recessive)
– BB
– Bb
– bb
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• So what colour eyes would a person have with the
following gene pairs?
Brown eyes
Blue eyes
Dark hair
Blond/red hair
Curly hair
Straight hair
Colour vision
Colour blindness
Normal sight
Night blindness
Normal blood
Haemophilia
Hearing
Congenital Deafness
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Dominant vs Recessive
Explain why…
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• Doug and Amber both have blonde hair. They
have two children, Alex and Sam. Alex has red
hair while Sam’s hair is dark brown.
Heritability
The extent to which the variability found in a
characteristic or trait is hereditary is known as the
heritability coefficient (score from 0 to 1)
O
100 %
down to
genes
For example, eye colour is solely determined by genes so has a
heritability coefficient of 1. Height is slightly influenced by
environment and has a heritability coefficient of 0.9
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100 % down to
environment
1
What about psychology?
• Where would you place these traits?
100 % down to
environment
• Memory, extraversion, academic achievement,
verbal reasoning, intelligence, spatial reasoning
1
100 %
down to
genes
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O
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