1. AP Psychology
2.2 Behavioral Genetics

2. 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)

3. 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)

4. Evolutionary Psychologists
Behavioral Geneticists
Study how natural selection favored behaviors that contributed to survival and spread of our ancestors genes
Look at universal behaviors shared by all people
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

5. 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

7. 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)

8. 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

9. 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 **

12. 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

14. 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

16. 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

18. 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

20. 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

22. 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

24. Recessive trait with ONE carrier

25. Recessive trait with TWO carriers

26. Dominant with ONE carrier

27. Dominant with TWO carriers

28. Genetic Disorders
Tay-Sachs syndrome – recessive trait that produces progressive loss of nervous function and death in a baby

29. 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

30. 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

32. Genetic Disorders
Huntington’s disease – dominant gene defect that involves degeneration of the nervous system, characterized by tremors, jerky motions, blindness, and death

34. 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

36. 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!