Transcript AP Psychology - Coshocton High School

AP Psychology
2.2 Behavioral Genetics
Genetics
Besides the functioning of the endocrine and
nervous system, genetics is another biological
factor that affects human behavior and thought
• Behavioral Genetics – Genetic and
environmental contributions to personality
and behavior
• Human traits are usually caused by genes
acting together (not usually one gene)
Nature vs. Nurture
• Influence on behavior (ex…body shape,
introversion, temper)
• Gene-Environment Interaction (sometimes
hard to determine because genes cause
someone to chooser their enviroment)
– Nature – heredity (genes determine)
– Nurture – environment or life history (begins in
prenatal period)
Evolutionary Psychologists
• Study how natural selection
favored behaviors that
contributed to survival and
spread of our ancestors
genes
• Look at universal behaviors
shared by all people
Behavioral Geneticists
• Study the role played by our
genes and our environment
in personality
characteristics and behavior
(mental ability, emotional
stability, temperament,
personality, interests, etc.)
• Look at the cause of our
individual differences
• Gene-environment
Interaction – choose
environ because of genes
Twin Studies
• Help separate the contributions of heredity
and environment
• Zygote – fertilized egg
• Identical (monozygotic) twins
– Two individuals who share all of the same
genes/heredity because they develop from the
same zygote
• Fraternal (dizygotic) twins
– Siblings that share about half of the same genes
because they develop from two different zygotes
Twin Studies
• Heritability – variation among individuals that is
due to genetic causes (genes)
• When twins grow up in the same environment,
the extent to which identical twins are
behaviorally more similar than fraternal twins
reveal the contribution of heredity
• If fraternal twins are separated at birth and raised
in different environments (adoption
studies)…behavioral differences may reveal the
contribution of environment to behavior;
similarities reveal the contribution of heredity
• Adoption studies – kids resemble biological
(nature), resemble adoptive family (nurture)
Thomas Bouchard study
• Found 100 identical twins given up for adoption
and raised in different families
• Studied hundreds of traits and determined the
influence on them (nature vs nurture)
• Example – IQ
• Correlation coefficient of .69 for identical twins
living apart
• .88 for identical twins living together
• Showed environment has some effect
• Living apart was still a moderate-strong
correlation – showed IQ heavily influenced by
genetics
Genetic Concepts
• Genome - the entirety of an organism's
hereditary information (book)
• Chromosome – structure in the nucleus of
cells that contains genes determined by DNA
sequences. (chapters of the book)
• Gene – each DNA segment of a chromosome
that determines a trait (words/paragraphs)
• DNA (deoxyribonucleic acid) – genetic
material that makes up chromosomes (letters)
• ** Traits are usually influenced by genes
acting together **
Human Cells
• 46 chromosomes in 23 pairs
– 23 from the sperm of the father
– 23 from the egg of the mother
• Father contributes a Y sex chromosome (23rd
pair), the baby is male; otherwise the baby is
female
– Males have 44 chromosomes plus X and Y
– Females have 44 chromosomes plus X and X
• All of the cells of the embryo/baby have the
same 23 pairs of chromosomes which carry
the genes for the same traits
Chromosomal Abnormalities
• Occasionally, chromosomes will combine (or
fail to) in an unusual way (errors in
fertilization) called mutations
• Turner’s Syndrome – females with only one X
sex chromosome
– Shortness, webbed necks, lack ovaries, fail to
develop secondary sex characteristics at puberty
– Usually normal intelligence – although cognitive
deficits in arithmetic, spatial organization, visual
perception
Chromosomal Abnormalities
• Klinefelter’s Syndrome – males with XXY
chromosomes
• At puberty, male secondary sex characteristics
fail to develop, but breast tissue does
(minimal sexual development)
• Tend to be passive / introversion
Chromosomal Abnormalities
• Down syndrome – three copies of
chromosome-21
• Typically mentally retarded
• Have a round head, flat nasal bridge,
protruding tongue, small round ears, a fold in
the eye lid (far apart), poor muscle tone and
coordination, short fingers and toes
Genetic Disorders
• Genotype – genetic make-up of an individual
• Phenotype – the expression of the genes
• Gene-environment interaction - term used to
describe any phenotypic effects that are due
to interactions between the environment and
genes
Genetic Disorders
• Homozygous – Possessing two identical forms of a
particular gene, one inherited from each parent (both)
/ individuals express that phenotypic characteristic
• Heterozygous – Possessing two different forms of a
particular gene, one inherited from each parent (aka
hybrid)
• Dominant gene – gene expressed when the genes for a
trait are different
• Recessive gene – the gene that is hidden or not
expressed when the genes for a trait are different
• Allele (uh-leel) – a dominant or recessive variant of a
particular gene (usually through mutation)
• Mutation – random error in gene replication
Recessive trait with ONE carrier
Recessive trait with TWO carriers
Dominant with ONE carrier
Dominant with TWO carriers
Genetic Disorders
• Tay-Sachs syndrome – recessive trait that
produces progressive loss of nervous function
and death in a baby
Genetic Disorders
• Albinism – recessive trait that produces a lack
of pigment and involves abnormal nerve
pathways to the brain resulting in quivering
eyes and inability to perceive depth (3D) with
both eyes
Genetic Disorders
• Phenylketonuria (PKU) – recessive trait that
results in severe, irreversible brain damage unless
the baby is fed a special diet low in phenylalanine
within 30 days of birth
• Individuals must regulate intake of phenylalanine
(artificial sweeteners – aspartame – NutraSweet /
Equal)
• The infant lacks the enzyme to process this amino
acid which can build up and poison the nervous
system
• Gene-environment interaction
Genetic Disorders
• Huntington’s disease – dominant gene defect
that involves degeneration of the nervous
system, characterized by tremors, jerky
motions, blindness, and death
Genetic Disorders
• Sex-linked traits – recessive genes located on
the X chromosome with no corresponding
gene on the Y chromosome, which results in
expression of recessive trait, more frequently
in males
– Color-blindness – individual cannot see certain
colors, most often red and green
– Baldness
• 25 percent of men begin balding by age 30; two-thirds
begin balding by age 60
• There is a 4 in 7 chance of receiving the baldness gene
– Hemophilia – long time for blood to clot
Genetic Disorders
• Alzheimer’s disease – most common form of
dementia (loss of cognitive functioning)
• A form has been attributed to a gene on
chromosome 21, but not in all cases!