1. Genetic Basis of Psychology

2. 3.4 What Is the Genetic Basis of Psychological Science?
Explain how genes are transmitted from parent to offspring
Discuss the goals and methods of behavioral genetics
Explain how both environmental factors and experience influence genetic expression
3.4 What Is the Genetic Basis of Psychological Science?
All of Human Development Has a Genetic Basis
Heredity Involves Passing Along Genes through Reproduction
Genotype and Phenotype
Polygenic Effects
Genetic Variation Is Created by Sexual Reproduction
Genes Affect Behavior
Behavioral Genetics Methods
Understanding Heritability
Social and Environmental Contexts Influence Genetic Expression
Genetic Expression Can Be Modified
Critical Think Skill: Seeking Disconfirming Evidence
Summing Up: What Is the Genetic Basis of Psychological Science?
Measuring Up

3. What Is the Genetic Basis of Psychological Science?
The term genetics is typically used to describe how characteristics are passed along to offspring and to the processes involved in turning genes “on” and “off”
Genetic predispositions are important in determining the environments we select for ourselves
Biology and environment mutually influence each other
The idea that genotype may influence environment may be new to students. A good example of this is temperament, which is primarily determined by heredity. For example, a temperamentally “difficult” baby may evoke different responses than an “easy” baby. The two types of temperaments will create two different environments.

4. All of Human Development Has a Genetic Basis
The genome is the master blueprint for making an entire organism
“The genome provides the option, and the environment determines which option is taken” (Marcus, 2004)
Chromosomes: made of deoxyribonucleic acid (DNA), consisting of two intertwined strands of molecules in a double helix shape
Genes: segments of DNA strands
Human Genome Project: mapped the entire structure of human DNA

5. FIGURE 3.29 The Human Body Down to Its Genes
Each cell in the human body includes pairs of chromosomes, which consist of DNA strands. DNA has a double helix shape and is composed of genes.

6. FIGURE 3.30 Human Genome Project
A map of human genes is presented by J. Craig Venter, president of the research company Celera Genomics, at a news conference in Washington on February 12, This map is one part of the international effort by hundreds of scientists to map the entire structure of human genetic material.

7. Heredity Involves Passing Along Genes through Reproduction
Mendel (ca. 1866): cross-pollinated different colored pea plants to see which color flowers the plants would produce
Discovered clues to the mechanisms responsible for heredity
Dominant gene:expressed whenever it is present in either parent
Recessive gene:expressed only when it is matched with a similar gene from the other parent

8. FIGURE 3.31 Genotypes and Phenotypes
Mendel’s experiments with crossbreeding pea plants resulted in purple flowers 75 percent of the time and white flowers 25 percent of the time.

9. Genotype and Phenotype
Genotype: an organism’s genetic makeup; never changes
Phenotype: an organism’s observable physical characteristics; always changing
Genetics (nature) and environment (nurture) both influence phenotype

10. Polygenic Effects
Polygenic trait: a trait that is influenced by many genes
The range of skin tones among Americans shows that human skin color is not inherited the same way as flower color was in Mendel’s research
Skin tone is not the end product of a single dominant/recessive gene pairing (genotype) but rather shows the effects of multiple genes
In addition to physical traits, psychological and behavioral traits, such as IQ and altruism, are polygenic.

11. Genetic Variation Is Created by Sexual Reproduction
From any two parents, 8 million different combinations of the 23 chromosomes are possible
The human zygote grows through cell division; errors sometimes occur during cell division and lead to mutations
Mutations produce an ability or behavior that may be advantageous/disadvantageous to the organism

12. FIGURE 3.32 Sex Chromosomes
(a) In females, the 23rd pair of chromosomes consists of two X chromosomes. (b) In males, the 23rd pair consists of one X and one Y chromosome. The Y chromosome is much smaller than the X chromosome.

13. FIGURE 3.34a Mutations
(a) These moths illustrate industrial melanism at work. As shown here, it is easier to spot light-colored insects against dark backgrounds. Because predators have an easier time catching insects they can spot, darker moths and darker butterflies are better able to survive in morepolluted areas.

14. Genes Affect Behavior
A person’s abilities and psychological traits are influenced by the interaction of genes and environment
Behavioral genetics: the study of how genes and environment interact to influence psychological activity
People are born like “undeveloped photographs”: The image has been captured, but the way it eventually appears depends on the development process

15. Behavioral Genetics Methods
Behavioral geneticists use two methods to assess the degree to which traits are inherited:
Twin studies: compare similarities between monozygotic (identical) and dizygotic (fraternal) twins to determine the genetic basis of specific traits
Greater similarity of monozygotic twins (raised together or apart) is likely due to genetic influence
Adoption studies: compare biological relatives and adoptive relatives

16. FIGURE 3.35a Twins
(a) Fraternal twins, such as this pair pictured during their 13th birthday party, result when two separate eggs are fertilized at the same time.

17. FIGURE 3.35b Twins
(b) Identical twins result when one fertilized egg splits in two. Identical twins Gerald Levey and Mark Newman, participants in Dr. Bouchard’s study, were separated at birth. Reunited at age 31, they discovered they were both firefighters and had similar personality traits.
What other factors might account for the similarities between twins raised apart?

18. Understanding Heritability
Heritability: a statistical estimate of the genetic portion of the observed variation in some specific trait
Heritability refers to populations, not to individuals
Example: In a certain population, height has a heritability of .60, which means 60 percent of height variation among individuals in that population is genetic. It does not mean that any one individual gets 60 percent of his or her height from genetics and 40 percent from environment
Estimates of heritability are concerned only with the extent that people differ in terms of their genetic makeup within the group

19. Social and Environmental Contexts Influence Genetic Expression
Caspi et al. (2002) followed more than 1,000 New Zealanders from birth until adulthood
Every few years information was collected about the participants
When the participants were 26 years old, investigators examined which factors predicted who had become a violent criminal
Mistreatment at home + low MAO gene accounted for nearly 50 percent of criminality
Study is a good example of how genes and social context interact to affect behavior (phenotype)

20. FIGURE 3.36 Scientific Method: Caspi's Study of the Influence of Environment and Genes

21. Genetic Expression Can Be Modified
Gene manipulation techniques can enhance or reduce the expression of a particular gene; genes from one animal species can be inserted into the embryo of another
Changing a single gene can dramatically change behavior
Example: A gene from the highly social prairie vole was inserted into the developing embryos of normally antisocial mice. The resulting transgenic mice exhibited social behavior more typical of prairie voles (Insel& Young, 2001)
Changing one gene’s expression leads to the expression of other genes, which ultimately influences behavior

22. FIGURE 3.37 Genetic Modifications
The two white mice and three brown mice in this photo are genetically normal. The sixth mouse is hairless because it has been genetically modified. Specifically, this mouse has received two nu genes, which cause the “nude” mutation. These genes also cause the mouse to have no thymus and therefore no T cells (an important part of the immune system). The lack of T cells makes the mouse a good laboratory subject, as its body cannot reject tumors or transplants of cells from other animals.

23. 3.5 How Does the Brain Change?
Explain how environmental factors and experience influence brain organization.
Describe sex differences in brain structure and function.
3.5 How Does the Brain Change?
The Interplay of Genes and Environment Wires the Brain
Cell Identity Becomes Fixed Over Time
Experience Fine-Tunes Neural Connections
Culture Affects the Brain
The Brain Rewires Itself throughout Life
Change in the Strength of Connections Underlies Learning
Changes in the Brain
The Puzzles of Synthesia
Critical Thinking Skill: Recognizing Unstated Assumptions
Females’ and Males’ Brains Are Similar and Different
The Brain Can Recover from Injury
Summing Up: How Does the Brain Change?
Measuring Up
Psychology: Knowledge You Can Use—Will My Learning Disability Prevent Me from Succeeding in College?

24. How Does the Brain Change?
Despite the great precision and the specificity of its connections, the brain is extremely malleable
Plasticity: a property of the brain that allows it to change as a result of experience, drugs, or injury

25. The Interplay of Genes and Environment Wires the Brain
Nature and nurture constantly interact to affect DNA’s activity and the products of that activity
Brain plasticity reflects the interactive nature of our biological and environmental influences

26. Cell Identity Becomes Fixed Over Time
As an embryo develops, each cell becomes more and more committed to its identity
Tissue transplanted early enough completely transforms into whatever type is appropriate for its new location; transplanting cells too late may disfigure the organism
Many people are excited about the possibility of transplanting fetal cells because they are undeveloped enough to become any type of tissue

27. Experience Fine-Tunes Neural Connections
Experience is important for normal brain development and maybe even more so for superior development
Example:
One group of rats was raised in a “normal” lab environment (featureless boxes with bedding at the bottom, plus dishes for food and water); another group was raised in an enriched environment
The “enriched” group developed bigger, heavier brains than the first group (Rosenzweig, Bennett, & Diamond, 1972)

28. Culture Affects the Brain
Our cultural experiences contribute to different patterns of brain activity
Example:
One group of participants in Japan and another group in the United States were shown pictures of both neutral and fearful facial expressions portrayed by Japanese and American faces.
Activity in the amygdala was greatest when participants viewed fearful expressions within their own cultural group (Chiao et al., 2008)

29. FIGURE 3.39 Scientific Method: Chiao's Study of How Culture Affects the Brain

30. The Brain Rewires Itself throughout Life
Although brain plasticity decreases with age, the brain can grow new connections among neurons and even grow new neurons into very old age
The rewiring and growth within the brain represents the biological basis of learning

31. Change in the Strength of Connections Underlies Learning
Changes in the brain due to experience are mainly in the strength of existing connections
Hebb’s “fire together, wire together” catchphrase: When two neurons fire simultaneously, the synaptic connection between them strengthens
Entirely new connections can grow between neurons.
Neurogenesis: New neurons are produced in some brain regions (e.g., the hippocampus)
Neurogenesis may underlie neural plasticity

32. Changes in the Brain
Wiring in the brain is affected by amount of use (e.g., recall the London taxi drivers)
Phantom limb: the intense sensation that an amputated body part still exists
Phenomenon suggests that the brain has not reorganized in response to the injury and that the missing limb’s cortical representation remains intact
An amputee who has lost a hand may, when his or her eyes are closed, perceive a touch on the cheek as if it were on the missing hand (Ramachandran&Hirstein, 1998)

33. FIGURE 3.40 Cortical Remapping Following Amputation
The participant felt a cotton swab touching his cheek as touching his missing hand.
What is the apparent reason for this effect?

34. The Puzzles of Synesthesia
Synesthesia: For synesthetes, sensory experiences are crossed
One man reported the he hates driving because the sight of road signs tastes to him like a mixture of pistachio ice cream and ear wax (McNeil, 2006)
The brain area involved in seeing colors is physically close to the brain area involved in understanding numbers, thus people with color/number synesthesia, may have some connections or cross- wiring between brain areas (Ramachandran& Hubbard, 2001)

35. Females’ and Males’ Brains Are Similar and Different
Females and males differ in their life experiences and hormonal makeup, which leads to differences between their brains
Males tend to have larger brains
Females and males may solve some complex problems differently, with females using language-related brain regions and males using spatial- related brain regions (Haier et al., 2005)
Brain areas important in processing language are more likely to be found in both halves of females’ brains than in males’ brains

36. FIGURE 3.43 Male versus Female Brains
A considerable body of evidence indicates that female brains are more bilaterally organized for language. For example, researchers studied men and women listening to someone reading aloud. As these fMRI images show, (a) the men listened with one side of their brains, whereas (b) the women tended to listen with both sides.

37. The Brain Can Recover from Injury
Following an injury in the cortex, the surrounding gray matter assumes the function of the damaged area
Radical hemispherectomy: After the surgical removal of an entire cerebral hemisphere, the remaining hemisphere eventually takes on most of the lost hemisphere’s functions
One of the most exciting (and controversial) areas of neurological research is the transplantation of human fetal tissue (stem cells) into the brain to repair damage
Instead of using fetal stem cells, new methods are emerging that allow researchers to create stem cells by reprogramming adult cells