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Summary IBP Introduction to Psychology Focus questions chapters 3 and 4
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IBP Introduction to Psychology Focus questions chapters 3 and 4
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• Animal welfare → The animals need to be taken care of properly, and unnecessary suffering must not beimplied. This also indicates the researchers’ responsibility of ensuring that the benefits of the study would
outweigh or at least balance the harm or deprivation caused to the animals.
Chapter 3:
1. How can genes affect behavioral traits through their role in protein synthesis?
• All the effects that genes have on behavior occur through their role in building and modifying the physical
structures of the body.
• Those structures, interacting with the environment, produce behavior
2. What does it mean to say that genes can influence behavioral traits only through interaction with the environment?
How are genes involved in long-term behavioral changes that derive from experience?
• Environment, as used in this context, refers to every aspect of an individual and his or her surroundings except
the genes themselves.
• the internal chemical environment of the individual
3. How can the same genotype produce various phenotypes?
• The same genes can have different effects, depending on the environment and the mix of other genes.
• Two individuals with the same genotype can be quite different in phenotype as a result of differences in their
environments
4. How does meiosis produce egg or sperm cells that are all genetically different from one another?
• During meiosis, each chromosome replicates itself once, but then the cell divides twice.
• Before the first cell division, the chromosomes of each pair line up next to one another and exchange genetic
material in a random manner
• egg or sperm cell produced is genetically different from any other egg or sperm cell and contains only half of
the full number of chromosomes
5. What is the advantage of producing genetically diverse offspring?
• By producing diverse offspring, parents are reducing the chance that all of their offspring will die as a result of
some unforeseen change in the environment.
6. What is the difference between a dominant and a recessive gene (or allele)?
• A dominant gene (or allele) is one that will produce its observable effects in either the homozygous or the
heterozygous condition
• A recessive gene (or allele) is one that will produce its effects in the homozygous condition only
7. Why do three-fourths of the offspring of two heterozygous parents show the dominant trait and one-fourth show
the recessive trait?
8. Why might a disease caused by two recessive genes persist in the gene pool?
• Although having two recessive genes for sickled cells was often a death sentence before the advent of modern
medicine, having just one recessive gene and one normal, dominant gene provided some benefit.
• The genes associated with sickle-cell anemia originated in areas of the globe
• People who have one recessive gene (carriers) living in these areas are thus more likely to live to reproduce
than noncarriers
9. How did Scott and Fuller show that the difference in fearfulness between cocker spaniels and basenji hounds is
controlled by a single gene locus, with the “fear” allele dominant over the “nonfear” allele?
, • conducted an experiment involving breeding the dogs and observing their behaviour towards humans. Basenjis
were afraid of humans, cocker spaniels were not intimidated. Researchers interbred the 2 species and found that
all the cocker spaniel – basenji hybrids (F1) showed fear towards humans thus concluded that fear in these
species was determined by a single dominant gene locus. They cross-breed the F1 hybrids and found that three
quarters would show fear and one quarter wouldn’t (F2).
10. Why would it be a mistake to conclude, from Scott and Fuller’s work, that fear in dogs is caused just by one gene
or that it is caused just by genes and not by the environment?
• Many different genes must contribute to building the complex neural structure needed to experience fear and
express it in behavior.
• Scott and Fuller’s work demonstrates only that the difference between cocker spaniels and basenji hounds in a
particular test of fear is controlled by a single gene
11. How do genes and the environment interact to affect individuals with PKU?
• phenylketonuria, or PKU, infants inherit two recessive genes involved in the processing of the amino acid
phenylalanine
• However, PKU only has its detrimental effects if the person consumes foods that contain phenylalanine.
• genetic disease, genes and environment clearly interact
12. How does the distribution of scores for a polygenic trait differ from that usually obtained for a single-gene trait?
• single-gene traits→ can be placed into one of two groups – there is either the genes’ possible effects, or not. It
is easy to detect the frequency; it depends on the genetic structure of the parents, the individual and the chances
of these single genes being passed on to the offspring is easy to calculate
• polygenic traits→, many more than one gene is responsible for a trait so the severity of the trait can be placed
on a spectrum. A normal distribution of this trait would form a scale with the most scores in the middle with
the prevalence decreasing towards the two extremes.
13. How are the characteristics of animals shaped through selective breeding?
• mating of individuals that lie toward the same extreme on the measure in question. For single-gene
characteristics the effects of selective breeding are immediate, but for polygenic characteristics the effects are
gradual and cumulative over generations.
• The members of each generation that best approximated the desired type were mated to produce the next
generation, resulting in a continuous genetic molding toward the varieties we see today.
14. How did Tryon produce “maze bright” and “maze dull” strains of rats? How did he show that the difference was
the result of genes, not rearing?
• he mated the males and females that had made the fewest errors in the maze to begin what he called the “maze
bright” strain and those that had made the most errors to begin the “maze dull” strain
15. Why is the strain difference produced by Tryon not properly characterized in terms of “brightness” or “dullness”?
• Tryon referred to his two strains of rats as “bright” and “dull,” but all he had measured was their performance
in a particular type of maze.
• Tryon’s “dull” rats could simply have been those that had less acute vision, or were less interested in the variety
of food used as a reward, or were more interested in exploring the maze’s blind alleys
16. How might a better understanding of epigenetics change the way we view genetic inheritance?
• to shed light on the biological basis of inheritance, including ways in which experiences during a person’s
lifetime might influence the phenotype of his or her grandchildren, as well as defining a bit more clearly the
nature of gene– environment interactions
17. What insight led Darwin to his theory of evolution? How is natural selection similar to and different from artificial
selection?
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