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Introductory Psychology Concepts
Genetics
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© 2011 The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Genetics
Chromosomal Abnormalities,
a few examples:
Down Syndrome:
A cause of mental retardation resulting
from the presence of an extra chromosome.
Klinefelter’s Syndrome,
or XXY syndrome:
Males inherit an extra X chromosome. Associated with taller than
average stature and impaired language skills.
Turner Syndrome:
Females have a missing X chromosome resulting in short stature
and impaired spatial intelligence.
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© 2011 The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Genetics
Genetics:
Dominant
If a gene in the pair received by mother and
father is dominant, the characteristic that it
controls will be displayed.
Recessive
If a gene received from one parent is
recessive, the characteristic will not show up
unless the partner gene from the other
parent is also recessive.
Polygenic Effects
When a number of gene pairs combine their
influences to create a single phenotypic trait,
this is known as polygenic transmission.
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© 2011 The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Genetics
Behavior Genetics
Heredity
The transfer of characteristics from parent to
offspring through their genes.
Interaction of Nature
Considering an individual’s innate qualities
(nature) in determining individual differences
in physical and behavioral traits.
Nurture
Considering environmental causes and
personal experiences in the determination of
physical and behavioral traits. Includes the
influence of parents, siblings, family, friends,
schooling, nutrition, and all other
experiences to which a child is exposed
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© 2011 The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Genetics
Twin Studies
Understanding behavior based on the amount of shared
genetic material
Two kinds of twins.
Identical (monozygotic) twins come from a single egg and sperm as a
result of a division of the zygote. They have all of their genes in common.
Sperm
Egg
One sperm and
one egg
Zygote divides
Two zygotes with
identical chromosomes
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© 2011 The McGraw-Hill Companies, Inc.
Identical twins (1 in 250 births)
Introductory Psychology Concepts: Genetics
Twin Studies
Understanding behavior based on the the amount of shared
genetic material
Two kinds of twins.
Fraternal (dizygotic) twins result from two eggs fertilized by two sperm.
They share only half of their genes.
Two eggs and
two sperm
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Two zygotes with
different chromosomes
© 2011 The McGraw-Hill Companies, Inc.
Fraternal twins (1 in 150 births)
Introductory Psychology Concepts: Genetics
Genetics
Heritability: Estimating the impact of genetic influence
Heritability Estimates for Various Human Characteristics
Trait
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Heritability Estimate
Height
.80
Weight
.60
Intelligence
.70
School Achievement
.40
© 2011 The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Genetics
Genetics
Heritability: Estimating the impact of genetic influence
Heritability Estimates for Various Human Characteristics
Personality
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Heritability Estimate
Extraversion
.36
Conscientiousness
.28
Agreeableness
.28
Neuroticism
.31
© 2011 The McGraw-Hill Companies, Inc.
Introductory Psychology Concepts: Genetics
Genetics
Heritability: Estimating the impact of genetic influence
Heritability Estimates for Various Human Characteristics
Temperament
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Heritability Estimate
Emotional reactivity
.40
Activity level
.25
Sociability
.25
Impulsivity
.45
© 2011 The McGraw-Hill Companies, Inc.