Chap 4 - Genetics and Evol of behavior Flashcards Preview

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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


Mendelian Genetics

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


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



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

deoxyribonucleic acid (DNA)


DNA serves as a model for the synthesis of:

ribonucleic acid (RNA)



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


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



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



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


Genes are either dominant, recessive, or intermediate

Examples: eye color, ability to taste PTC


dominate gene

shows a strong effect in either the homozygous or heterozygous condition


recessive gene

shows its effect only in the homozygous condition


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


Some genes are only expressed partly:

in some cells and not others or only under certain circumstances


Autosomal genes

all other genes except for sex- linked genes


sex-linked genes

genes located on the sex chromosomes


In mammals, the sex chromosomes are designated X & Y

- Females have two X chromosomes (XX)

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


durin reproduction:

- females contribute an X chromosome

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


female offspring



male offspring



human Y chromosome has genes for

27 proteins


human X chromosome has genes for approx

1500 proteins


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

e.g., red-green color deficiency


sex-limited genes

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


genes change in several ways:

- mutation
- microduplication/ microdeletion



heritable change in a DNA molecule


microduplication/ microdeletion

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



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


Epigenetic differences are a likely explanation for differences between:

monozygotic “identical” twins


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


Almost all behaviors have both:

a genetic component and an environmental component


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

- monozygotic
- fraternal



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


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


Genes do not directly produce:


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


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



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


Evolution attempts to answer two questions:

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


How species did evolve involves the tentative construction of:

“evolutionary trees”


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


artificial selection

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


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



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.”


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


Some behaviors are more debatable regarding the influence of natural selection

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


Altruistic behavior

a behavior that benefits someone other than the actor

- Altruism is hard to find outside of humans


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


group selection

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


kin selection

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


reciprocal altruism

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


brain development depends upon:

- maturation
- learning


we can refine this understanding by learning how:

- neurons develop
- their axons connect
- experience modifies development


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


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


development of neurons in the brain involves the following processes:

- proliferation
- migration
- differentiation
- myelination
- synaptogenesis



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



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



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



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



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


Originally believed that ____ new neurons were formed after early development



Later research suggests otherwise for neuron development:

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


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


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


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


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



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


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


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


Fetal Alcohol Syndrome

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


Fetal alcohol syndrome marker by:

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


Exposure to alcohol in the fetus brain:

suppresses glutamate and enhances the release of GABA


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



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


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

prefrontal cortex


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


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


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


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

new branching of axons and dendrites


Possible causes of brain damage:

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


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


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

Common cause of brain damage in elderly


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



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


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


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


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


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