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Introductory Psychology Concepts
Genetics
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© 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.
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.
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
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
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
Two zygotes with
different chromosomes
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
Heritability Estimate
Height
Weight
Intelligence
School Achievement
.80
.60
.70
.40
Introductory Psychology Concepts: Genetics
Genetics
Heritability: Estimating the impact of genetic influence
Heritability Estimates for Various Human Characteristics
Personality
Extraversion
Conscientiousness
Agreeableness
Neuroticism
Heritability Estimate
.36
.28
.28
.31
Introductory Psychology Concepts: Genetics
Genetics
Heritability: Estimating the impact of genetic influence
Heritability Estimates for Various Human Characteristics
Temperament
Emotional reactivity
Activity level
Sociability
Impulsivity
Heritability Estimate
.40
.25
.25
.45