Chapter 4: Genetics, Evolution, Development & Plasticity

Question 1

Suppose you have high sensitivity to tasting PTC. If your mother can also taste it easily, what (if anything) can you predict about your father’s ability to taste it?

Answer 1

If your mother has high sensitivity to the taste of PTC, we can make no predictions about your father. You may have inherited a high-sensitivity gene from your mother, and because the gene is dominant, you need only one copy of the gene to taste PTC

Question 2

Suppose you have high sensitivity to the taste of PTC. If your mother has low sensitivity, what (if anything) can you predict about your father’s taste sensitivity?

Answer 2

If your mother has low sensitivity, you must have inherited your high-sensitivity gene from your father, so he must have high sensitivity.

Question 3

Suppose someone identifies a “gene for” certain aspects of development. How might that statement be misleading?

Answer 3

Almost any characteristic depends on more than one gene, as well as influences from the environment.

Question 4

How does a sex-linked gene differ from a sex-limited gene?

Answer 4

A sex-linked gene is on the X or Y chromosome. A sex-limited gene is on an autosomal chromosome, but activated in one sex more than the other.

Question 5

How does an epigenetic change differ from a mutation?

Answer 5

A mutation is a permanent change in part of a chromosome. An epigenetic change is an increase or decrease in the activity of a gene or group of genes.

Question 6

How does adding a methyl or acetyl group to a histone protein alter gene activity?

Answer 6

Adding a methyl group turns genes off. An acetyl group loosens histone’s grip and increases gene activation.

Question 7

What are the main types of evidence to estimate the heritability of some behavior?

Answer 7

One type of evidence is greater similarity between monozygotic twins than dizygotic twins. Another is resemblance between adopted children and their biological parents. A third is a demonstration that a particular gene is more common than average among people who show a particular behavior.

Question 8

Suppose someone determines the heritability of IQ scores for a given population. Then society changes in a way that provides the best possible opportunity for everyone within that population. Will heritability of IQ increase, decrease, or stay the same?

Answer 8

Heritability will increase. Heritability estimates how much of the variation is due to differences in genes. If everyone has the same environment, then differences in environment cannot account for much of the remaining differences in IQ scores. Therefore, the relative role of genetic differences will be greater.

Question 9

What example illustrates the point that even if some characteristic is highly heritable, a change in the environment can alter it?

Answer 9

Keeping a child with the PKU gene on a strict low-phenylalanine diet prevents the mental retardation that the gene ordinarily causes. The general point is that sometimes a highly heritable condition can be modified environmentally.

Question 10

Many people believe the human appendix is useless. Will it become smaller and smaller with each generation?

Answer 10

No. Failure to need a structure does not make it smaller in the next generation. The appendix will shrink only if people with a gene for a smaller appendix reproduce more successfully than other people do

Question 11

What are plausible ways for possible altruistic genes to spread in a population?

Answer 11

Altruistic genes could spread because they facilitate care for one’s kin or because they facilitate exchanges of favors with others (reciprocal altruism). Group selection may also work under some circumstances, especially if the cooperative group has a way to punish or expel an uncooperative individual.

Question 12

What is a sex-linked gene?
A. A gene that influences sexual behavior
B. A gene that has greater effects on one sex than the other
C. A gene on either the X or Y chromosome
D. A gene that becomes activated during sexual behavior

Answer 12

A gene on either the X or Y chromosome

Question 13

What is a sex-limited gene?
A. A gene that influences sexual behavior
B. A gene that has greater effects on one sex than the other
C. A gene on either the X or Y chromosome
D. A gene that becomes activated during sexual behavior

Answer 13

A gene that has greater effects on one sex than the other

Question 14

What does a microdeletion remove?
A. Part of a protein
B. Part of a brain wave
C. Part of a chromosome
D. Part of a neuron

Answer 14

Part of a chromosome

Question 15

How does an epigenetic change differ from a mutation?
A. An epigenetic change is a duplication or deletion of part of a gene.
B. An epigenetic change alters gene activity without replacing any gene.
C. An epigenetic change alters more than one gene at a time.
D. An epigenetic change is beneficial, whereas a mutation is harmful.

Answer 15

An epigenetic change alters gene activity without replacing any gene

Question 16

How does adding a methyl or acetyl group to a histone protein alter gene activity?
A. A methyl group turns genes off. An acetyl group loosens histone’s grip and increases gene activation.
B. A methyl group turns genes on. An acetyl group tightens histone’s grip and decreases gene activation.
C. A methyl group increases the probability of a mutation, whereas an acetyl group decreases the probability.
D. A methyl group decreases the probability of a mutation, whereas an acetyl group increases the probability.

Answer 16

A methyl group turns genes off. An acetyl group loosens histone’s grip and increases gene activation.

Question 17

Most estimates of heritability of human behavior use what type(s) of evidence?
A. Studies of changes in behavior as people grow older
B. Studies of similarities between parents and children
C. Comparisons of twins and studies of adopted children
D. Comparisons of people living in different cultures

Answer 17

Comparisons of twins and studies of adopted children

Question 18

What is the difference between monozygotic (MZ) and dizygotic (DZ) twins?
A. MZ twins develop from two eggs, whereas DZ twins develop from a single egg.
B. MZ twins develop from a single egg, whereas DZ twins develop from two eggs.
C. MZ twins are one male and one female, whereas DZ twins are of the same gender.
D. MZ twins are of the same gender, whereas DZ twins are one male and one female.

Answer 18

MZ twins develop from a single egg, whereas DZ twins develop from two eggs.

Question 19

Which of the following offers strong evidence that environmental changes can largely counteract the effect of a gene?
A. The effects of temperature on children with autism spectrum disorder
B. The effects of diet on children with phenylketonuria (PKU)
C. The effects of muscle training on children who have suffered a concussion
D. The effects of sleep on children with malaria

Answer 19

The effects of diet on children with phenylketonuria (PKU)

Question 20

Which of these is responsible for evolutionary changes in a species?
A. Using or failing to use part of the body increases or decreases its size for the next generation.
B. A gene that has long-term benefits to the species will become more common.
C. Individuals with certain genes reproduce more than average.
D. Evolutionary changes anticipate the adaptations that will be advantageous in the future.

Answer 20

Individuals with certain genes reproduce more than average.

Question 21

What, if anything, can we predict about the future of human evolution?
A. People will get smarter, wiser, and more cooperative.
B. People will not change, because evolution no longer affects humans.
C. People will become more like whichever people tend to have the most children.
D. We cannot make any of these predictions.
11.

Answer 21

People will become more like whichever people tend to have the most children.

Question 22

Why do human infants show a grasp reflex?
A. The reflex is an accidental by-product of brain development.
B. The reflex is an imitation of actions the infant sees adults doing.
C. The reflex helps the infant develop motor skills that will be helpful later.
D. The reflex was advantageous to infants of our remote ancestors.

Answer 22

The reflex was advantageous to infants of our remote ancestors.

Question 23

Donella and Hershel are having a baby. Donella is a heterozygous high-taster for phenylthiocarbamide (PTC). Hershel is a homozygous low-taster for PTC. What is the chance their offspring will be a low-taster?
a. 15 percent
b. 25 percent
c. 75 percent
d. 50 percent

Answer 23

50 percent

Donella would be Tt and Hershel would be tt. This means that the four possible Punnett square options would be Tt, Tt, tt, and tt. This means that there is a 50 percent chance that the offspring will be a low-taster (tt).

Question 24

The field of _____ deals with changes in organisms due to changes in gene expression rather than changes in the genetic code.
a. homogenetics
b. Mendelian genetics
c. epigenetics
d. heterogenetics

Answer 24

Epigenetics

Epigenetics studies how numerous factors such as life experience alter gene expression. For instance, epigeneticists would study the effect of alcohol consumption or other drug use on the offspring of that parent.

Question 25

Which of the following is the best evidence against the idea that “use or disuse of some structure or behavior [results in] an evolutionary increase or decrease in that feature”?
a. The idea of little toes getting smaller because we don’t use them
b. A parent exercising his/her arm muscles but having children with normal-size muscles
c. A drug-using mother giving birth to an addicted baby
d. Lamarckian evolution

Answer 25

A parent exercising his/her arm muscles but having children with normal-size muscles

The flawed logic that the prevalence of a feature or behavior will automatically increase that feature evolutionarily is best demonstrated by the idea that using a structure (for example, muscles used by a parent) does NOT result in the child having greater than average muscles. Similarly, just because we don’t “use our little toes” does not mean that they are going away (despite rumors suggesting they are).

Question 26

Which comes first: migration, synaptogenesis, or myelination?

Answer 26

Migration occurs first

Question 27

New receptor neurons form in which sensory system?

Answer 27

Olfaction

Question 28

What evidence indicates that new neurons form in the human hippocampus and basal ganglia?

Answer 28

The mean C14 concentration of the DNA of human neurons in the hippocampus and basal ganglia corresponds to a level slightly more recent than the year the person was born, indicating that some of those neurons formed after birth

Question 29

What was Sperry’s evidence that axons grow to a specific target instead of attaching at random?

Answer 29

If he cut a newt’s eye and inverted it, axons grew back to their original targets, even though the connections were inappropriate to their new positions on the eye

Question 30

If axons from the retina were prevented from showing spontaneous activity during early development, what would be the probable effect on development of the thalamus?

Answer 30

The axons would attach based on a chemical gradient but could not fine-tune their adjustment based on experience. Therefore, the connections would be less precise.

Question 31

What process assures that the spinal cord has the right number of axons to innervate all the muscle cells?

Answer 31

The nervous system builds more neurons than it needs and discards through apoptosis those that do not make lasting synapses

Question 32

What class of chemicals prevents apoptosis in the sympathetic nervous system?

Answer 32

Neurotrophins, such as nerve growth factor

Question 33

At what age does a person have the greatest number of neurons—early in life, during adolescence, or during adulthood?

Answer 33

The neuron number is greatest early in life.

Question 34

Anesthetic drugs and anxiety-reducing drugs increase activity of GABA, decreasing brain excitation. Why would we predict that exposure to these drugs might be dangerous to the brain of a fetus?

Answer 34

Prolonged exposure to anesthetics or anxiety-reducing drugs might increase apoptosis of developing neurons. Increased GABA activity decreases excitation, and developing neurons undergo apoptosis if they do not receive enough excitation.

Question 35

In the ferret study, how did the experimenters determine that visual input to the auditory portions of the brain actually produced a visual sensation?

Answer 35

They trained the ferrets to respond to stimuli on the normal side, turning one direction in response to sounds and the other direction to lights. Then they presented light to the rewired side and saw that the ferret again turned in the direction it had associated with lights.

Question 36

An enriched environment promotes growth of axons and dendrites in laboratory rodents. What is known to be one important reason for this effect?

Answer 36

Animals in an enriched environment are more active, and their exercise enhances growth of axons and dendrites

Question 37

Name two kinds of evidence indicating that touch information from the fingers activates the occipital cortex of people blind since birth.

Answer 37

First, brain scans indicate increased activity in the occipital cortex while blind people perform tasks such as feeling two objects and saying whether they are the same or different. Second, temporary inactivation of the occipital cortex blocks blind people’s ability to perform that task, without affecting the ability of sighted people.

Question 38

Which brain area shows expanded representation of the left hand in people who began practicing stringed instruments in childhood and continued for many years?

Answer 38

Somatosensory cortex (postcentral gyrus) of the right hemisphere.

Question 39

What change in the brain is responsible for musician’s cramp?

Answer 39

Extensive practice of violin, piano, or other instruments causes expanded representation of the fingers in the somatosensory cortex, as well as displacement of representation of one or more fingers in the motor cortex. If the sensory representation of two fingers overlaps too much, the person cannot feel them separately or move them separately.

Question 40

Why is immaturity of the prefrontal cortex not a satisfactory explanation for risky behaviors in adolescents?

Answer 40

As the teenage years progress, risky behavior tends to increase, even though the prefrontal cortex is becoming more mature.

Question 41

What is one way in which older adults compensate for less efficient brain functioning?

Answer 41

Many of them compensate by activating additional brain areas.

Question 42

In early brain development, what is the relationship between the sensory systems and muscle movements?
A. The sensory systems develop before the first muscle movements.
B. The first muscle movements occur at the same time as when the sensory systems develop.
C. The first muscle movements occur before the sensory systems develop.
D. First vision develops, then movements, and then the other sensory systems.

Answer 42

The first muscle movements occur at the same time as when the sensory systems develop.

Question 43

Which parts of the cerebral cortex are most likely to deteriorate in Alzheimer’s disease and other conditions?
A. The areas that mature at the earliest ages, such as the primary visual cortex.
B. The areas most distant from the heart, such as the parietal cortex.
C. The areas responsible for emotional processing, such as the amygdala.
D. The areas that mature at the latest age, such as the prefrontal cortex.

Answer 43

The areas that mature at the latest age, such as the prefrontal cortex.

Question 44

In which areas of the human brain do some new neurons develop during adulthood?
A. The primary visual cortex and the primary auditory cortex
B. The hippocampus and the basal ganglia
C. The olfactory bulbs and the areas responsible for speech
D. The corpus callosum and the cerebellum

Answer 44

The hippocampus and the basal ganglia

Question 45

When Sperry cut a newt’s optic nerve and turned the eye upside down, what happened?
A. Axons of the optic nerve grew randomly and attached diffusely to target cells.
B. Axons of the optic nerve grew back to their original targets.
C. Axons of the optic nerve grew back to targets appropriate to their new location in the eye.
D. At first the axons grew back randomly, but then they established appropriate connections by learning.

Answer 45

Axons of the optic nerve grew back to their original targets.

Question 46

In the sympathetic nervous system, which of the following prevents apoptosis?
A. Steroid hormones
B. Nerve growth factor
C. Physical exercise
D. Myelination

Answer 46

Nerve growth factor

Question 47

Why does the spinal cord have the right number of axons to innervate all the muscle cells?
A. Each muscle cell sends a chemical message telling the spinal cord to make a neuron.
B. The genes cause a certain number of neurons to form and the same number of muscles to form.
C. Immature cells divide, with one daughter cell becoming a neuron and the other becoming a muscle.
D. The spinal cord makes an excess of neurons, but those that fail to innervate a muscle die.

Answer 47

The spinal cord makes an excess of neurons, but those that fail to innervate a muscle die.

Question 48

At what age does a person have the largest number of neurons?
A. Before or shortly after birth
B. Equally at all times of life
C. Adolescence
D. Adulthood

Answer 48

Before of shortly after birth

Question 49

If a pregnant woman drinks alcohol, alcohol harms the brain of the fetus not only while it is in the system, but also while it is washing away after drinking. What is the danger while alcohol is washing away?
A. Temperature in the brain may decrease.
B. Blood pressure in the brain may decrease.
C. Excess inhibition at GABA synapses can lead to apoptosis.
D. Overstimulation at glutamate synapses can poison the mitochondria.

Answer 49

Overstimulation at glutamate synapses can poison the mitochondria.

Question 50

In the ferret study, what evidence indicated that visual input to the auditory portions of the brain actually produced a visual sensation?
A. Bright flashes of light to the rewired eye caused the ferrets to blink both eyes.
B. Recordings from individual cells of the rewired temporal cortex showed the same patterns usually seen in cells of the occipital cortex.
C. Ferrets could find their way around an unfamiliar room even with the normal eye closed.
D. Ferrets that learned to turn one way in response to light in the normal eye turned the same way to light in the rewired eye.

Answer 50

Ferrets that learned to turn one way in response to light in the normal eye turned the same way to light in the rewired eye.

Question 51

An enriched environment including social interactions promotes growth of axons and dendrites in laboratory rodents. What else can produce the same effect?
A. Improved diet
B. Physical activity
C. Exposure to music
D. Extra sleep

Answer 51

Physical activity

Question 52

According to most research, what are the effects of computerized programs to practice memory skills?
A. Temporary improvement of the skills that were practiced
B. Temporary improvement of both the practiced skills and general intelligence (“far transfer”)
C. Long-term improvement of both the practiced skills and general intelligence (“far transfer”)
D. No benefits, not even temporarily

Answer 52

Temporary improvement of the skills that were practiced

Question 53

If a person is born blind, what happens to the occipital (“visual”) cortex?
A. Its cells shrink and gradually die.
B. Its cells remain intact but forever inactive.
C. Its cells become responsive to touch or hearing.
D. Its cells become spontaneously active, producing hallucinations.

Answer 53

Its cells become responsive to touch or hearing.

Question 54

In people who practice violin or other stringed instruments for many years, what changes in the cerebral cortex?
A. Both hemispheres begin controlling speech equally.
B. Parts of the occipital cortex stop responding to vision and switch to hearing.
C. A larger than average portion of the cortex responds to the passage of time.
D. A larger than average portion of the cortex responds to fingers of the left hand.

Answer 54

A larger than average portion of the cortex responds to fingers of the left hand.

Question 55

What causes musician’s cramp?
A. Changes in the muscles and tendons of the hand
B. Rewiring of the cerebral cortex
C. Loss of myelin on the motor nerves to the hand
D. Changes in the touch receptors of the hand

Answer 55

Rewiring of the cerebral cortex

Question 56

What is the most likely biological explanation for increased risky behavior among adolescents?
A. Immaturity of the prefrontal cortex
B. Increased activity in brain areas that anticipate reward
C. Increased activity in brain areas responsible for depressed mood
D. Immaturity of the corpus callosum

Answer 56

Increased activity in brain areas that anticipate reward

Question 57

Why do many older people continue to hold important jobs in spite of the declines in memory and brain function that are known to occur in old age?
A. Laws prevent them from being fired.
B. Most of their jobs don’t require much brain activity.
C. Old people take the credit for work that younger people actually do.
D. The declines on average do not apply to all people.

Answer 57

The declines on average do not apply to all people.

Question 58

What are the two kinds of stroke, and what causes each kind?

Answer 58

The more common form, ischemia, is the result of an occlusion of an artery. The other form, hemorrhage, is the result of a ruptured artery

Question 59

Why is tPA not helpful in cases of hemorrhage?

Answer 59

The drug tPA breaks up blood clots, and hemorrhage results from a ruptured blood vessel, not a blood clot.

Question 60

After someone has had a stroke, would it be best (if possible) to direct stimulant drugs to the cells that were damaged or somewhere else?

Answer 60

It is best to direct a stimulant drug to the cells that had been receiving input from the damaged cells. Presumably, the loss of input has produced diaschisis

Question 61

Is collateral sprouting a change in axons or dendritic receptors?

Answer 61

Axons

Question 62

Is denervation supersensitivity a change in axons or dendritic receptors?

Answer 62

Dendritic receptors

Question 63

What is responsible for the phantom limb experience?

Answer 63

Synapses that used to receive input from the now amputated part become vacant. Axons representing another part of the body take over those synapses. Now stimulation of this other part activates the synapses associated with the amputated area, but that stimulation feels like the amputated area.

Question 64

A monkey that loses sensation from one arm stops using it, but a monkey that loses sensation from both arms does use them. Why?

Answer 64

A monkey that lost sensation in one arm is capable of moving it, but finds it easier to walk with the three intact limbs. When both arms lose their sensations, the monkey is forced to rely on them.

Question 65

At birth an average human brain will weigh about _____ grams, whereas an adult brain is closer to_____ grams.
a. 350; 1,300
b. 1,300; 1,500
c. 500; 2,000
d. 350; 2,000

Answer 65

350; 1300
When a human is born, the brain weighs about 350 grams. During the first year of life, the brain will go from 350 grams to around 1,000 grams. By the time you are an adult, your brain should weigh between 1,200 and 1,400 grams (median 1,300).

Question 66

Dr. Weiss’s interpretation of his hypothesis about chemical pathfinding by axons was proven wrong. Instead, evidence showed that axons locate where they are going by ______.
a. following chemical trails
b. moving in sync with neighboring axons because each is in the presence of muscle tissue
c. receiving many signals but only responding to one
d. listening only to muscles

Answer 66

Following chemical trails

Although his experiments with salamanders worked, his interpretation of the results was incorrect. We now know that there are various chemicals that serve as a guide for axonal migration and growth. These chemicals seem to be region specific.

Question 67

We know that as people grow older, their behavior changes. Related, we know that one of the changes that occurs as people age is that they become less impulsive and have less trouble deciding future choices. Out of these individuals and knowing what we know, who would have the MOST trouble with future choices?
a. Zoë, 9-year-old female
b. LeeFredrick, a 28-year-old male
c. Mary, a 28-year-old female
d. Terrance, a 60-year-old male

Answer 67

Zoe, 9-year old female

The child would have the most trouble given that she is only 9. The prefrontal cortex, which is responsible for those behaviors, tends to finish developing in a person’s late teens/early 20s. Also, females tend to develop a little sooner than males.

Question 68

Which of the following is the most common cause of brain damage in older individuals?
a. Infection
b. Alzheimer’s disease
c. Closed head injury
d. Stroke

Answer 68

Stroke

Many older individuals are at risk for cardiovascular issues, including stroke. There are several types of stroke, but all result in disrupted blood supply to portions of the brain.

Question 69

Recently, Jonah and his friend, Landon, were in a car accident. Jonah had been studying neuroscience at school. As such, he had the time and presence of mind to _____ right before the cars collided to prevent excessive brain injury.
a. tuck his chin to his chest and hold his neck muscles stiff
b. lean his head back
c. brace with his legs and keep his neck loose
d. aim his head away from the air bags and keep his neck loose

Answer 69

Tuck his chin to his chest and hold his neck muscles stiff

Often, brain injury in a car accident occurs when the brain hits up against your skull during the movement of your head in the crash. If you have time, you can prevent this by tucking your head down and trying to brace your neck instead of leaving your neck muscles loose. Although you will still have whiplash, the impact on your brain will be lessened.

Question 70

Recent studies have shown that exposure to the active chemical in marijuana can reduce some of the effects of a stroke in laboratory animals. It is hypothesized that this is because the drug reduces the release of _____ following the stroke.
a. serotonin
b. GABA
c. glutamate
d. dopamine

Answer 70

Glutamate

Although it is a neurotransmitter, excessive exposure to glutamate is toxic to neurons. Glutamate is also released following stroke and other brain injuries, which further causes damage. The THC in marijuana is thought to prevent the excessive glutamate release following stroke.

Question 71

Tissue plasminogen activator (tPA) is helpful in reducing the effect of a stroke only under which of these conditions?
A. It is helpful only if the stroke was due to a hemorrhage.
B. It is helpful only if administered within the first hours after a stroke.
C. It is helpful only if the patient practices relevant movements while taking the drug.
D. It is effective only for laboratory animals, not for humans.

Answer 71

It is helpful only if administered within the first hours after a stroke.

Question 72

What would be the purpose of giving a drug that stimulates dopamine receptors to a stroke patient?
A. To break up blood clots in the nervous system
B. To increase collateral sprouting
C. To combat diaschisis
D. To stimulate regrowth of axons

Answer 72

to combat diaschisis

Question 73

Name two procedures that decrease the damage caused by strokes in laboratory animals, although physicians so far have seldom tried them with people.
A. Dehydration and lithium
B. Increased blood flow and antidepressants
C. Decreased body temperature and cannabinoids
D. Increased body temperature and tranquilizers

Answer 73

Decreased body temperature and cannabinoids

Question 74

In which species, if any, can axons regrow in the spinal cord?
A. In humans only
B. In fish
C. In birds
D. In no species

Answer 74

In Fish

Question 75

Where does collateral sprouting take place?
A. In the cell body
B. In the axon
C. In the dendrites
D. In both the axons and the dendrites

Answer 75

In the axon

Question 76

Where does denervation supersensitivity take place?
A. In the blood flow to the brain
B. In glia cells
C. At synapses
D. In axon membranes

Answer 76

At synapses

Question 77

What causes the phantom limb experience?
A. Irritation of receptors at the stump where the amputation occurred
B. Spontaneous activity of receptors at the stump where the amputation occurred
C. Reorganization of the sensory cortex
D. A psychiatric reaction based on denial of the amputation

Answer 77

Reorganization of the sensory cortex

Question 78

Suppose a patient uses only the right arm following injury that blocked all sensation from the left arm. Of the following, which is the most promising therapy?
A. Electrically stimulate the skin of the left arm.
B. Tie the right arm behind the person’s back.
C. Blindfold the person.
D. Increase visual stimulation on the right side of the body.

Answer 78

Tie the right arm behind the person’s back.