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Heredity: Our Genetic
• Heredity is transmission of characteristics
from parents to offspring
- Physical traits – height, hair, & eye color
- Psychological traits like – shyness,
leadership, & aggressiveness; interested
in arts & crafts
• Disorders such as anxiety, depression,
schizophrenia, bipolar disorders, &
alcoholism
Genes & Chromosomes
• Genes are the basic building blocks of heredity
- Traits are pairs of genes, with one gene in each
pair inherited from each parent
* Blood type (single pair of genes); Intelligence
(combinations of genes)
• Chromosomes found in DNA
- Most normal human beings have 46
chromosomes (organized into 23 pairs)
- Psychologists try to find clues of psychological
traits in how genes are paired
* Without 46, physical & behavioral disorders
result
Nature-Nurture Debate
• Nature refers to what people inherit – biological
groundwork that prepares a person to develop in
certain ways.
• Nurture refers to environmental factors – what a
person is exposed to in life; family, education,
culture, living conditions, & everyday individual
experiences
• How much of who we are is found in our genes
(nature) verses how we are raised & environmental
conditions (nurture)?
How Much Do You Have In
Common With Your Relatives?
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Identical Twins: 100% of their genes
Parents & Children: 50% of their genes
Brother & Sisters: 50% of their genes
Your Aunts & Uncles: 25% of their genes
Your 1st Cousins: 12.5% of their genes
Human Behavior Genetics
• Family Studies based on the assumptions that if
genes influence a trait, close relatives should share
that trait more often than distant relatives because
close relatives have more genes in common.
- For example, schizophrenia occurs in only 1 to
2% of the population. Siblings of schizophrenia
are about 8 times more likely, & the children
are about 10 times more likely, to develop the
disorder.
* However, families also share environments.
Twin Studies & Fraternal Twin
Studies
• Twin studies & fraternal twin studies have provided
evidence for the habitability of a # of behaviors,
ranging from verbal skills to aggressiveness, to
mannerism such as the strength of a handshake to
depression & anxiety.
- For example, when one identical twin develops
schizophrenia, the chances that the other twin
will develop the disorder are about 50%. For
fraternal twins, the chances are about 15%.
* The higher rate exhibited by twins,
particularly identical twins, suggests that
heredity plays a crucial role in schizophrenia.
Adoptive Studies
• Adoptive studies focus on children who were
adopted at birth & brought up by parents not
genetically related to them, & evidence for the
habitability of intelligence & some forms of mental
illness & in behavior thought to be solely
determined by environmental influences.
- For example, of the 47 people whose adopted
mother suffered from schizophrenia, 5 adoptees
subsequently suffered as well.
* With a control group, however, there was
not a single case.
Record both psychological & physical traits that you share
with members of your family! Identify if the traits are
nature or nurture.
Psychological & Physical Traits
Heredity: Nature
1. Color of my eyes
2. Work ethic
3. Height
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4. Personality
5. Sense of Humor
6. Hair Color
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7. Athleticism
Environmental: Nurture
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8. Physical Make-up
9. Intelligence
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10. Determination
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