PSYC1003 Study Guide - Final Guide: Twin, Xyy Syndrome, Chromosome Abnormality
Biology and Developmental Psychology
Genetic Foundations
• There’s natural variation in the human population – physical, cognitive (eg: IQ) and
behavioural.
• Genetics is the 'nature' side of the Nature-Nurture debate.
• Psychology interfaces with genetics: genotype + environment = phenotype.
Genetics: Basics
• Humans have 46 chromosomes - 22 pairs of autosomes, 2 sex chromosomes.
• On each chromosome there are a set of genes, which code for organism functions either in
isolation or through interaction with other genes.
• We inherit traits from our familial group - half from mother and half from father.
Genetic Disorders:
• There are some 7000 known genetic disorders.
• Disorders caused by dominant genes, eg: Huntington's Disease - nervous system deterioration
after the age of 40.
• Disorders caused by recessive genes, eg: Phenylketonuria - inability to metabolise
phenylalanine (an amino acid found in food).
o Phenylalanine accumulates in blood, causing severe cognitive deficits and other
abnormalities → death by 30.
o Newborns can be screened at birth - avoid phenylalanine by special diet = genetic-
environment interaction.
• Chromosomal abnormalities - errors in cell division during gamete formation (sperm and
ovum) resulting in genetic abnormalities, eg: Down Syndrome (Trisomy 21 - 3 copies of
chromosome 21) → low IQ, memory and speech problems, limited vocab, motor problems
and congenital eye, ear, heart and intestinal defects.
• Polygenic Inheritance - variables of interest to developmental psychologists are not typically
determined by singular genetic abnormalities, eg: no "IQ gene".
• Abnormalities of Sex Chromosomes:
Syndrome
Characteristics
Incidence
Turer’s sydroe XO
Female, short, webbed neck, heavy build, infertile, poor
memory.
1/5000
Poly-X Syndrome (XXX)
Female, tall, fertile, impaired verbal intelligence.
1/1000
Kliefelter’s XXY
Male, very tall, sterile, female body type with low male
hormone level, impaired verbal intelligence.
1/900
XYY Syndrome
Male, tall, fertile, near-normal intelligence.
1/1000
Behavioural Genetics
• Behavioural genetics - aims to determine the contributions of nature and nurture to
behavioural diversity.
• Heritability - the proportion of a given behaviour that is due to genetics rather than
environmental factors.
• Two types of natural experiments allow us to tease apart genetics from environment:
1. Twin Studies:
• Identical (monozygotic) twins - splitting of single fertilised egg. Same DNA/same environment.
• Fraternal (dizygotic twins) - separate fertilisation of two eggs. Different DNA/same
environment.
• Logic of twin studies: identical twins - fraternal twins = (genetic + environment) - environment.
• What is left is the genetic contribution to the trait.
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