Chap 4 - Genetics and Evol of behavior Flashcards Preview

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1

Genetics and behavior

- review of genetics provides a springboard for evaluating this controversial question

- Both genes and enviro interact to shape human behavior

- fundamental issue is how much a role each factor plays in shaping human behaviors

Ex: psychological disorders, weight gain, personality, sexual orientation

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Mendelian Genetics

19th century monk Gregor Mendel demonstrated that inheritance occurs through GENES

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Genes are aligned along ________ (strands of genes) and come in pairs

chromosomes

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A gene is a portion of a chromosome and is composed of:

deoxyribonucleic acid (DNA)

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DNA serves as a model for the synthesis of:

ribonucleic acid (RNA)

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RNA

single strand chemical that can serve as a template/ model for the synthesis of proteins

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Proteins determine the development of the body by:

- Forming part of the structure of the body

- Serving as enzymes, biological catalysts that regulate chemical reactions in the body

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homozygous

a person has an identical pair of genes on the two chromosomes

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heterozygous

a person has an unmatched pair of genes on the two chromosomes

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Genes are either dominant, recessive, or intermediate

Examples: eye color, ability to taste PTC

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dominate gene

shows a strong effect in either the homozygous or heterozygous condition

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recessive gene

shows its effect only in the homozygous condition

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Examples such as PTC and hair color can be misleading

Implies that a single gene combination completely controls a characteristic, but this is not true

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Some genes are only expressed partly:

in some cells and not others or only under certain circumstances

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Autosomal genes

all other genes except for sex- linked genes

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sex-linked genes

genes located on the sex chromosomes

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In mammals, the sex chromosomes are designated X & Y

- Females have two X chromosomes (XX)

- Males have an X and a Y chromosome (XY)

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durin reproduction:

- females contribute an X chromosome

- Males contribute either X or Y = determines the sex of the child

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female offspring

XX

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male offspring

XY

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human Y chromosome has genes for

27 proteins

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human X chromosome has genes for approx

1500 proteins

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sex-linked genes usually refer to X-linked genes:

e.g., red-green color deficiency

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sex-limited genes

genes that are present in both sexes but mainly have an effect on one sex (chest hair, breast size, etc.)

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genes change in several ways:

- mutation
- microduplication/ microdeletion

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mutation

heritable change in a DNA molecule

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microduplication/ microdeletion

part of a chromosome that might appear once might appear twice or not at all

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Epigenetics

a field that is concerned with changes in gene expression without the modification of the DNA sequence

- Some genes are active only at a certain point in one’s life, a certain time of day, etc.

- Changes in gene expression are central to learning and memory

- Experiences alter the activity of genes

- What you do at any moment not only affects you now, but produces epigenetic effects that alter gene expressions for a longer period of time

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Epigenetic differences are a likely explanation for differences between:

monozygotic “identical” twins

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heredity and environment

Refers to how much characteristics depend on genetic differences

- Researchers have found evidence for heritability in almost every behavior they have tested

- Heritability of a certain trait is specific to a given population

- Strong environmental influences may cause genetic influences to have less of an effect

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Almost all behaviors have both:

a genetic component and an environmental component

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Researchers study ______ (“from one egg”) and ________ (“from two eggs”) twins to infer contributions of heredity and environment

- monozygotic
- fraternal

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Heritability

refers to how much characteristics depend on genetic differences

- certain trait is specific to a given population

- Strong environmental influences may cause genetic influences to have less of an effect

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Traits with a strong hereditary influence can by modified by:

environmental intervention

e.g., PKU: a genetic inability to metabolize the amino acid phenylketonuria

- Environmental interventions can modify PKU

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Genes do not directly produce:

behaviors

- Genes produce proteins that increase the probability that a behavior will develop under certain circumstances

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Genes can also have an indirect affect

Genes can alter your environment by producing behaviors or traits that alter how people in your environment react to you

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evolution

refers to a change in the frequency of various genes in a population over generations

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Evolution attempts to answer two questions:

1. how did some species evolve
2. how do species evolve

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How species did evolve involves the tentative construction of:

“evolutionary trees”

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How species do evolve rests upon some assumptions:

- Offspring generally resemble their parents for genetic reasons

- Mutations, recombination, and microduplications of genes introduce new heritable variations

- Certain individuals successfully reproduce more than others do

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artificial selection

refers to choosing individuals with desired traits and making them parents of the next generation

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According to _______, nature also selects, and successful individuals’ genes will be prevalent in later generations

Darwin

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Common misconceptions about evolution include the following:

- Lamarckian evolution: “The use or disuse of some structure or behavior causes an increase or decrease in that behavior.”

- “Humans have stopped evolving.”

- “Evolution means improvement.”

- “Evolution acts to benefit the individual or the species.”

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Evolutionary psychology

focuses upon functional and evolutionary explanations of how behaviors evolved

Assumes that behaviors characteristic of a species have arisen through natural selection and provide a survival advantage

Ex: differences in peripheral/color vision, sleep mechanisms in the brain, eating habits, temperature regulation

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Some behaviors are more debatable regarding the influence of natural selection

Ex include:
- Life span length
- Gender differences in sexual promiscuity
- Altruistic behavior

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Altruistic behavior

a behavior that benefits someone other than the actor

- Altruism is hard to find outside of humans

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A gene

- only spreads if individuals with it reproduce more than individuals w/o it

- that benefits the species but not the individual dies out w/ that individual

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group selection

is a controversial hypothesis that states that altruistic groups survive better than less cooperative ones

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kin selection

selection is the favored explanation: selection for a gene that benefit’s the individual’s relatives

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reciprocal altruism

is the idea that individuals help those that will return the favor

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brain development depends upon:

- maturation
- learning

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we can refine this understanding by learning how:

- neurons develop
- their axons connect
- experience modifies development

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The human central nervous system begins to form when the embryo is approximately 2 weeks old

- dorsal surface thickens, forming a neural tube surrounding a fluid filled cavity

- forward end enlarges and differentiates into the hindbrain, midbrain, and forebrain

- rest of the neural tube becomes the spinal cord

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development of the brain

The fluid-filled cavity becomes the central canal of the spinal cord and the four ventricles of the brain

at birth - 350 g
1st yr - 1000 g
adult - 1200-1400 g

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development of neurons in the brain involves the following processes:

- proliferation
- migration
- differentiation
- myelination
- synaptogenesis

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proliferation

production of new cells/ neurons in the brain primarily occurring early in life

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migration

movement of the newly formed neurons and glia to their eventual locations

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differentiation

forming of the axon and dendrites that gives the neuron its distinctive shape

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myelination

process by which glia produce the fatty sheath that covers the axons of some neurons

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synaptogenesis

final stage of neural development – the formation of the synapses between neurons

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Originally believed that ____ new neurons were formed after early development

No

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Later research suggests otherwise for neuron development:

- stem cells
- New olfactory receptors also continually replace dying ones

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stem cells

undifferentiated cells found in the interior of the brain that generate “daughter cells” that can transform into glia or neurons

- Stem cells differentiate into new neurons in the adult hippocampus of mammals and facilitate learning

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Development of new neurons also occurs in other brain regions

Ex: songbirds have a steady replacement of new neurons in the singing area of the brain

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pathfinding by axons

Axons must travel great distances across the brain to form the correct connections

- Growing axons reach their target area by following a gradient of chemicals in which they are attracted by some chemicals and repelled by others

- When axons initially reach their targets, they form synapses with several cells

- Postsynaptic cells strengthen connection with some cells and eliminate connections with others
The formation or elimination of these connections depends on the pattern of input from incoming axons

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Some theorists refer to the idea of the selection process of neural connections as:

neural Darwinism

- In this competition among synaptic connections, we initially form more connections than we need

- most successful axon connections and combinations survive while the others fail to sustain active synapses

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Levi-Montalcini

discovered that muscles do not determine how many axons form; they determine how many survive

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Nerve growth factor (NGF)

is a type of protein released by muscles that promotes the survival and growth of axons

- brain’s system of overproducing neurons and then applying apoptosis enables the exact matching of the number of incoming axons to the number of receiving cells

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vulnerability in brain development

- Early stages of brain development are critical for normal development later in life

- mutation on one gene can lead to many defects

- Chemical distortions in the brain during early development can cause sign impairment and developmental problems

- fetal alcohol syndrome

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Fetal Alcohol Syndrome

A condition that children are born with if the mother drinks heavily during pregnancy

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Fetal alcohol syndrome marker by:

- Hyperactivity and impulsiveness
- Difficulty maintaining attention
- Varying degrees of mental retardation
- Motor problems and heart defects
- Facial abnormalities

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Exposure to alcohol in the fetus brain:

suppresses glutamate and enhances the release of GABA

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Exposure to alcohol in the fetus brain:

suppresses glutamate and enhances the release of GABA

- Many neurons consequently receive less excitation and exposure to neurotrophins than usual and undergo apoptosis

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adolescents

tend to be more impulsive than adults

- Impulsivity can be a problem when it leads to drinking, risky driving, sex, etc

-tend to discount the future

- are not equally impulsive in all situations

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The _______ of adolescents is relatively inactive in certain situations, but this may or may not be the cause of impulsivity

prefrontal cortex

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old age

Some neurons lose their synapses, and the remaining synapses change more slowly than before in response to experiences

- brain structures begin to lose volume

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research underestimates older people:

- People vary in respect to intellectual decline

- Older people have a greater base of knowledge and experience, and many find ways to compensate for losses

78

brain plasticity

- Almost all survivors of brain damage show behavioral recovery to some degree

- Some recovery relies on the growth of new branches of axons and dendrites

- Understanding the processes of recovery will give us new and improved therapies

- Most survivors of brain damage show some degree of behavioral recovery

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Some of the mechanisms of recovery include those similar to the mechanisms of brain development such as the:

new branching of axons and dendrites

80

Possible causes of brain damage:

- Tumors
- Infections
- Exposure to toxic substances or radiation
- Degenerative diseases
- Closed head injuries

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A closed head injury refers to a sharp blow to the head that does not puncture the brain

- One of the main causes of brain injury in young adults

- After a severe injury, recovery can be slow and incomplete

82

A stroke or cerebrovascular accident is temporary loss of blood flow to the brain

Common cause of brain damage in elderly

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later mechanisms of recovery

Following brain damage, surviving brain areas increase or reorganize their activity

- Diaschisis

- Drugs (stimulants) may stimulate activity in healthy regions of the brain after a stroke

- Destroyed cell bodies cannot be replaced, but damaged axons do grow back under certain circumstances
= axon in the peripheral nervous system is crushed, it follows its myelin sheath back to the target and grows back toward the periphery at a rate of about 1 mm per day

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Diaschisis

decreased activity of surviving neurons after damage to other neurons

- Because activity in one area stimulates other areas, damage to the brain disrupts patterns of normal stimulation

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Damaged axons do not readily regenerate in a mature mammalian brain or spinal cord

- Scar tissue makes a mechanical barrier to axon growth

- Neurons on the two sides of the cut pull apart

- Glia cells that react to CNS damage release chemicals that inhibit axon growth

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regrowth of axons

- Research on building protein bridges may help

- Axon Sprouting

- Collateral sprouts are new branches formed by other non-damaged axons that attach to vacant receptors

- Cells that have lost their source of innervation release neurotrophins that induce axons to form collateral sprouts

- Over several months, the sprouts fill in most vacated synapses and can be useful, neutral, or harmful

87

Phantom limb:

the continuation of sensation of an amputated body part

- Cortex reorganizes itself after the amputation of a body part by becoming responsive to other parts of the body

- Original axons degenerate leaving vacant synapses into which others axons sprout

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The phantom limb can lead to the feeling of sensations in the amputated part of the body when other parts of the body are stimulated

e.g., a touch on the face can bring about the experience of a phantom arm

- Use of an artificial limb can reduce the likelihood of experiencing phantom limb