Genetics, evolution, development and plasticity

Question 1

Mendelian Genetics

Answer 1

During the nineteenth century, Gregor Mendel demonstrated that inheritance occurs through genes (units of heredity that maintain their identity from one generation to the next).

• As a rule, genes come in pairs, as they are aligned along chromosomes (strands of genes). One exception to this rule is male sex chromosomes, which do not come in pairs.
• A gene is a portion of a chromosome, which is composed of a double-stranded chemical called deoxyribonucleic acid (DNA).
• A strand of DNA serves as a template (model) for the synthesis of ribonucleic acid (RNA).

Question 2

Homozygous and heterozygous

Answer 2

If individuals have an identical pair of genes on the two chromosomes, they are homozygous for that gene; if they instead have an unmatched pair of genes, they are heterozygous for that gene (e.g., a gene for black hair on one chromosome and a gene for brown hair on the other).

Question 3

Dominant genes:

Answer 3

Dominant genes show a strong effect in either homozygous or heterozygous conditions

Question 4

Recessive genes:

Answer 4

show their effects only in homozygous conditions (e.g., a carrier for both a dominant black hair gene and a recessive brown hair gene will have black hair).

Question 5

sex-linked genes

Answer 5

Genes located on sex chromosomes
- All other chromosomes are referred to as autosomal chromosomes. Genes located on autosomal chromosomes are autosomal genes.

Question 6

Sex-limited genes:

Answer 6

Genes present in both sexes but active mainly in one sex (that affect chest hair growth, or breast development).

Question 7

Mutation:

Answer 7

A heritable change in a DNA molecule.

- Mutations are rarely advantageous. One rare example: FOXP2 gene, which facilitates language development.

Question 8

Epigenetics:

Answer 8

Changes in gene expression without modification of the DNA sequence (e.g., brain changes resulting from drug addiction).
- Experiences act by altering the activity of genes.

Question 9

high heritability:

Answer 9

when the variations in some characteristic depend largely on genetic differences

Question 10

Heritability in humans is studied in three ways:

Answer 10

1. Comparing monozygotic (identical) twins and dizygotic (fraternal) twins (virtual twins are children from different biological families who are the same age and are raised in the same household at the same time)
2. Studying adopted children and their biological parents
3. Identifying specific genes linked to some behaviour
   - Using these methods, researchers have found significant heritability of almost every behaviour they have tested except for religious affiliation

Question 11

Phenylketonuria, or PKU:

Even a trait with high heritability can be modified by environmental interventions

Answer 11

A genetic inability to metabolize the amino acid phenylalanine. If PKU is not treated, phenylalanine accumulates to toxic levels, impairing brain development and leaving a child mentally retarded, restless, and irritable. Although PKU is a hereditary condition, environmental interventions can modify it.
c. By having a strict diet low in phenylalanine

Question 12

Evolution:

Answer 12

Change over generations in the frequencies of various genes in a population.

Question 13

Artificial selection:

Answer 13

Breeding animals for desirable individual characteristics (this causes changes in various genetic frequencies in a population).

Question 14

fitness:

Answer 14

operationally defined as the number of copies of one’s genes that endure in later generations.

Question 15

Evolutionary psychology:

Answer 15

Concerns how behaviors evolved.

Question 16

Altruistic behavior:

Answer 16

Behaviors that benefit others rather than the individual committing the behavior.

Question 17

kin selection:

Answer 17

selection for a gene that benefits the individual’s relatives. A gene spreads if it causes you to risk your life to protect your children, who share many of your genes, including perhaps a gene for altruism.

Question 18

reciprocal altruism:

Answer 18

the idea that individuals help those who will return the favor.

Question 19

Growth and Development of Neurons The five steps of neuron development:

Answer 19

a. Proliferation: Production of new cells; cells along the ventricles of the brain divide. Some cells remain where they are as stem cells, continuing to divide.
i. Nearly all neurons form within the first 28 weeks of gestation, premature birth before that times inhibits neuron formation
b. Others become primitive neurons and glia that migrate to other locations.
c. Early in development, the primitive neurons begin to migrate (move). Chemicals known as immunoglobins and chemokines guide the new cells to their eventual destination in the brain.
d. At first, a primitive neuron looks like any other cell. Gradually, the neuron differentiates, forming its axon and dendrites; the axon grows before the dendrites.
e. A later and slower stage of neuronal development is myelination, the process by which glia produce the insulating fatty sheaths that accelerate transmission in many vertebrate axons. Myelin forms first in the spinal cord and then in the hindbrain, midbrain, and forebrain. Experiencing social isolation impairs formation of myelin
f. The final stage is synaptogenesis, or the formation of synapses. Although this process begins before birth, it continues throughout life, as neurons form new synapses and discard old ones.

Question 20

Proliferation:

Answer 20

Production of new cells

Question 21

myelination:

Answer 21

the process by which glia produce the insulating fatty sheaths that accelerate transmission in many vertebrate axons.

Question 22

synaptogenesis:

Answer 22

or the formation of synapses

Question 23

Neural Darwinism:

Answer 23

During development of the nervous system, synapses form randomly before a selection process keeps some and rejects others (this is only partly accurate since synapse formation is also influenced by chemical guidance and neurotrophic factors).

Question 24

nerve growth factor (NGF):

Answer 24

Levi-Montalcini discovered that muscles produce NGF, which promotes the survival and growth of axons.

Question 25

apoptosis:

Answer 25

Programmed cell death where axons that don’t receive enough NGF degenerate and their cell bodies die. All neurons are born with this suicide program and will automatically die if the right synaptic connection is not made

Question 26

Neurotrophin:

Answer 26

a chemical (like NGF) that promotes the survival and activity of neurons. In addition to NGF, the brain also uses brain-derived neurotrophic factor (BDNF) as a neurotrophin.

Question 27

brain-derived neurotrophic factor (BDNF):

Answer 27

BDNF is the most abundant neurotrophin in the adult mammalian cortex.

Question 28

homeobox genes

Answer 28

A series of genes found in vertebrates, insects, plants, even fungi and yeast—regulate the expression of other genes and control the start of anatomical development

Question 29

Fetal alcohol syndrome (FAS):

Answer 29

Caused by alcoholic consumption during pregnancy. Symptoms include decreased alertness, hyperactivity, facial abnormalities, mental retardation, motor problems, and heart defects.
- Infant brains are especially sensitive to alcohol because it suppresses the release of glutamate, the brain’s main excitatory transmitter. Thus, neurons receive less excitation and undergo apoptosis

Question 30

Focal hand dystonia (musician’s cramp):

Answer 30

this happens in musicians who practice extensively when the expanded representation of each finger overlaps its neighbor. The fingers become clumsy, fatigue easily, and make involuntary movements that interfere with the desired task. A similar condition called “writer’s cramp” can happen to people who spend all day writing.

Question 31

Closed head injury:

Answer 31

A sharp blow to the head that does not actually puncture the brain. The most common cause of brain damage in young people. Closed head injuries damage the brain because of rotational forces (whiplash) that drive the brain tissue against the inside of the skull.

Question 32

Stroke (cerebrovascular accident):

Answer 32

A temporary loss of blood flow to the brain. This is a common cause of brain damage, especially in the elderly.

Question 33

Ischemia:

Answer 33

The most common type of stroke; loss of blood flow caused by a blood clot or other obstruction of an artery.

Question 34

Hemorrhage:

Answer 34

A less common type of stroke; bleeding due to the rupture of an artery.

Question 35

edema:

Answer 35

fluid accumulation

Question 36

tissue plasminogen activator (tPA) clot-busting drugs:

Answer 36

clot-busting drugs, which restore blood flow following ischemia, or by using drugs that antagonize glutamate activity.

• Can be used within 3 hours of initial stroke
• Appropriate treatment for ischemic stroke but would kill people with a haemorrhage

Question 37

Immediate Treatments for strokes

Answer 37

i. Decreasing cell death after a stroke can be accomplished by administering tissue plasminogen activator (tPA) clot-busting drugs, which restore blood flow following ischemia, or by using drugs that antagonize glutamate activity.
ii. The most effective known method of preventing brain damage after strokes in laboratory animals is to cool the brain. Cooling protects the brain after ischemia by reducing overstimulation, apoptosis, and inflammation.
iii. Exposure to cannabinoids (the chemicals found in marijuana) minimizes the damage caused by strokes in laboratory animals (found to be most effective if given before a stroke)

Question 38

Diaschisis:

Answer 38

Decreased activity of surviving neurons after other neurons are destroyed. Behavioral deficits due to diaschisis can sometimes be improved with the use of stimulant drugs.

Question 39

denervation supersensitivity or receptor super sensitivity:

Answer 39

If a certain set of synapses becomes inactive—perhaps because of damage elsewhere in the brain—the remaining synapses become more responsive, more easily stimulated.
- Denervation supersensitivity is a way of compensating for decreased input. However, the increased sensitivity can lead to intense responses in normal inputs, which can result in prolonged pain.

Question 40

collateral sprouts

Answer 40

After a cell loses input from an axon, it secretes neurotrophins that induce other axons to form new branches, or collateral sprouts, which take over the vacant synapses.