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• Next session: studying heritability– Reading– Preparation Qs

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Evolution

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 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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Evolution of phobia

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Today you will…

Learn about• The role and influence of

genes in humans

Learn how to• Describe biological

structures• Distinguish between

biological and psychological concepts

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How many can you define?

• Gene• Genetics• Heredity• Genotype• Phenotype• Dominant gene• Recessive gene

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What are genes?

• Genes are bits of DNA which make proteins– These proteins cause physiological responses in

the body• An organism’s genes convey information

about how to construct that organism from one generation to the next

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Genetics and heredity

• 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?

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Genotype vs Phenotype• 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?

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• How does this example illustrate the concepts of phenotype and genotype?– 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.

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Remember...

• Just because it’s in the genotype that doesn’t necessarily mean it’ll be expressed in the phenotype:– 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?

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• Genes are organised in chromosomes, these come in pairs – you inherit one half of each pair from each parent– Dominant genes are always expressed – Recessive genes are expressed only in the absence

of a dominant gene

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Which genes are expressed?

• Consider eye colour:B = brown eyes (dominant)b = blue eyes (recessive)

• So what colour eyes would a person have with the following gene pairs?– BB– Bb– bb

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Dominant vs Recessive

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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Explain why…

• 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.

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Heritability

O 1

100 % down to genes

100 % down to environment

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)

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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What about psychology?

• Where would you place these traits?

• Memory, extraversion, academic achievement, verbal reasoning, intelligence, spatial reasoning

O 1

100 % down to genes

100 % down to environment

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