CHAPTER 4: HEREDITY AND EVOLUTION
Questions included in web quizzing are marked in bold
Chapter Outline
I. Introduction
A. It was not until the 20th century that scientists understood how selective breeding could increase
the frequency of desirable characteristics.
B. The genetic principles described by Mendel form the basis of modern genetics.
2. The predominant belief centered on the blending of parental traits in the offspring, starting
with the Greek philosophers and even Darwin held this belief.
1. Mendel used these terms to account for the fact that the expression of one (recessive) trait in
the F1 generation was masked by the expression of the other (dominant) trait. These
1. Mendel also demonstrated that different characteristics aren’t necessarily inherited together
(ii) Genes that control plant height and seed color are located on different, non partner
2. Genetic disorders result from harmful alleles inherited in Mendelian fashion.
3. Traits may be inherited either as dominant or recessive alleles.
a. Dominant alleles cause a number of genetic disorders.
b. Recessive conditions are typically associated with the lack of a substance, usually an
enzyme. For a person to have a recessive disorder, he/she must have two copies of the
recessive allele that causes it.
(i) Individuals who have one copy of the harmful recessive allele are unaffected, but can
pass that allele onto offspring. They are termed carriers.
c. Blood groups provide one of the best examples of Mendelian traits.
(i). Alleles determine a person’s blood type by coding for the production of antigens.
d. Codominance exists where two different alleles are present and both are expressed.
2. Dominant alleles are not “stronger,” “better,” or more common than recessive alleles.
1. The alleles coding for melanin production have additive effects.
2. The effect of multiple alleles at several loci produces continuous variation in skin tone.
1. Most polygenic traits can be measured on a scale, hence are continuous traits.
2. Many Mendelian traits have known loci. However, polygenic traits cannot yet be traced to
specific loci.
VI. Genetic and Environmental Factors
A. For polygenic traits, many aspects of the phenotype are influenced by genetic-environmental
interactions. For many characteristics, it’s not possible to identify the specific environmental
components that influence the phenotype.
B. Mendelian traits are less likely to be influenced by the environment; yet even for polygenic
characteristics, Mendelian principles still apply at individual loci.
VII. Mitochondrial Inheritance
A. mtDNA is transmitted to the offspring only from the mother.
B. Because mtDNA is inherited from only one parent, meiosis and recombination do not occur.
C. This means that all the variation in mtDNA among individuals is caused by mutation, which
makes mtDNA extremely useful for studying genetic change over time.
D. All the variation in mtDNA among individuals is caused by mutation (mtDNA mutation rates
have been used to construct evolutionary relationships between primate species and between
living human populations.
VIII. Modern Evolutionary Theory
A. Modern evolutionary theory has its roots in the principles of natural selection formulated by
Darwin and Wallace, plus the rediscovery of Mendelian principles of inheritance. The competing
explanations of evolution offered by mutationists and selectionists were synthesized into a single
theory in the mid-1930s.
1. The production and redistribution of variation.
2. The process of natural selection acting on this variation.
1. Allele frequencies are indicators of the genetic makeup of a population, the members of
which share a gene pool.
B. Short-term evolutionary changes, such as allele frequency changes from one generation to the
next, are termed microevolution.
C. Long-term evolutionary effects that are evident in the fossil record are termed speciation, or
macroevolution.
1. Mutations must occur in the gametes (sperm or egg) to have evolutionary consequences.
2. Mutation rates tend to be low, and mutations alone tend to have little impact on changes in
1. Population movements (and the resulting exchange of genes) have been very high during the
2. Founder effect is a particular kind of drift that may occur when a small founding population
a. The loss of genetic diversity is termed a genetic bottleneck.
3. Both gene flow and genetic drift can produce some evolutionary changes, yet usually
1. This does not cause evolution, but it provides genetic combinations upon which natural
selection can act.
1. Directional changes in allele frequencies are a function of the environmental context.
2. If the environment changes, selection pressures change, and ultimately, allele frequencies
1. The HbS mutation occurs at a low frequency in all human populations.
2. In some populations, especially in western and central Africa, the HbS allele occurs in
frequencies approaching 20 percent.
a. The geographical correlation between the distribution of malaria and high frequencies of
the HbS allele indicates a biological relationship between the two.
b. Sickle-cell anemia trait results from inheriting two copies of the Hbs allele.
c. Sickle-cell anemia has numerous manifestations, but basically, the abnormal hemoglobin
S reduces the ability of red blood cells to transport oxygen throughout the body.
1. Mutations of the DNA in the gametes (the molecular level).
3. The individual is subject to natural selection (the level of the individual).
4. Populations are composed of individuals, and evolution is said to occur when allele
Hybrids
p. 74
Sickle Cell Anemia
p. 90
1. You can illustrate Mendelian principles in your class by calculating the frequencies for various
2. Collecting information from students regarding ABO and Rh blood groups is another useful
3. Have students construct their own family pedigree for a particular Mendelian trait. Again, the ABO
4. Explore the advances in the field of genetics and genetic testing which permit more accurate
1. Go to http://www.appalachianhistory.net/2010/06/blue-fugates-of-kentucky.html
and read about the Fugates of Kentucky. What genetic condition is responsible for their remarkable skin
color?
3. Visit the PBS website for a list of various activities and learning tools on genetics.
www.pbs.evolution.org
1. Gregor Mendel is known for which of the following?
a. He developed theories of evolutionary change.
b. He discovered the structure of the DNA molecule.
c. He studied characteristics that are influenced by several genetic loci.
d. He discovered the fundamental principles of how traits are inherited.
2. How do the basic principles of inheritance, identified by Mendel in plants, differ from those in
humans?
a. They are simpler.
b. Plants don’t have alleles.
c. There are no differences since the basic principles are the same.
d. There are no Mendelian traits in humans.
e. The number of chromosomes is different; therefore the genetic principles are different.
3. When Mendel crossed true breeding tall and short parental plants, what was produced?
a. All the offspring were tall.
b. Half the offspring were tall, the other half were short.
c. All the offspring were short.
d. The offspring were intermediate in height relative to the two parent plants.
4. In Mendel’s experiments, what was the ratio of tall to short plants in the F2 generation?
a. 15 to 1
b. 3 to 1
c. ½ tall, ½ short
d. 4 to 1
5. Which statement concerning the F1 plants in Mendel’s experiments is false?
a. They were hybrids.
b. They were heterozygous for the traits in question.
c. Their parents were homozygous for the traits in question.
d. All F1s displayed the dominant trait in their phenotype.
6. A person who is homozygous recessive at a locus has which of the following?
a. two copies of the recessive allele
b. two copies of the dominant allele
c. an autosomal trisomy
d. a recessive allele on the X chromosome only
7. What is the term for the condition of two copies of the same allele being present in the genotype?
a. dominant
b. codominant
c. recessive
d. homozygous
8. In Mendel’s experiments, the tall parental (P) plants
a. were homozygous for the allele for tallness
b. were heterozygous at the locus controlling height
c. could NOT be crossed with short plants
d. were homozygous for the allele for shortness
9. What is an individual’s actual genetic make-up called?
a. phenotype
b. homozygosity
c. recessiveness
d. phenotypic ratio
10. According to the principle of independent assortment there is a __________chance that any tall
pea plant will produce either yellow or green peas.
a. 0 percent
b. 25 percent
c. 50 percent
d. 75 percent
11. What is the term used to refer to the observable, physical expression of genotypes?
a. genotype
b. phenotype
c. phenotypic ratio
d. genotypic ratio
12. Mendelian traits
a. are governed by more than one genetic locus
b. occur only in some people
c. are always dominant
d. are governed by one genetic locus
13. Gregor Mendel
a. published his results and won the Nobel Prize for his discoveries
b. was trained as a geneticist
c. did not know about chromosomes
d. was a professor at the University of Vienna
14. The ABO blood type system consists of ______ alleles.
a. 6
b. 4
c. 3
d. 2
15. Which of the following is not a polygenic trait?
a. stature
b. skin color
c. eye color
d. ABO blood type
16. What is it called when a person possesses two different alleles at the same locus, and both alleles are
expressed in the phenotype?
a. recessiveness
b. codominance
c. dominance
d. homozygosity
17. What is type AB blood an example of?
a. codominance
b. blending
c. recessiveness
d. dominance
18. How many ABO phenotypes (blood types) are there?
a. 4
b. 2
c. 3
d. 6
19. Mendelian traits are described as discrete, or discontinuous because
a. Their phenotypic expressions overlap
b. Their phenotypic expressions do not fall into clearly defined categories
c. Their genotypic expression overlap
d. Their genotypic expressions do not fall into clearly defined categories
20. In a hypothetical situation, B is the allele that causes brachydactyly. If a man who has normal fingers
(bb) and a woman with brachydactyly (Bb) have children, what proportion of these children would
you expect to have normal fingers? (Hint: Use a Punnett square).
a. None
b. All
c. 1/4
d. 3/4
21. At a hypothetical locus, a man’s genotype is Aa. What proportion of his gametes would be
expected to receive the A allele?
a. All
b. ½
c. ¾
d. ¼
22. Two people (both heterozygotes) are able to taste a chemical substance called PTC. The ability to
taste PTC is caused by a dominant allele (T). The inability to taste PTC is caused by a recessive allele
(t). What proportion of their children would be expected to have the ability to taste PTC?
a. 3/4
b. 1/2
c. All
d. 1/4
23. Two people (both heterozygotes) are able to taste a chemical substance called PTC. The ability
to taste PTC is caused by a dominant allele (T). The inability to taste PTC is caused by a
recessive allele (t). What proportion of their children would be expected not to be able to taste
PTC?
a. 3/4
b. All
c. 1/4
d. 2/3
24. Two people (both heterozygotes) are able to taste a chemical substance called PTC. The ability
to taste PTC is caused by a dominant allele (T). The inability to taste PTC is caused by a
recessive allele (t). What proportion of their offspring would be expected to be heterozygous?
a. 3/4
b. 1/2
c. All
d. 1/4
25. Which of the following is not inherited in a Mendelian fashion?
a. Huntington Disease
b. albinism
c. cleft chin
d. Tay-Sachs disease
26. Which of the following types of traits are governed by more than one genetic locus?
a. polygenic
b. dominant
c. Mendelian
d. recessive
27. Which statement concerning polygenic traits is not true?
a. They are governed by more than one genetic locus.
b. Their expression is often influenced by genetic/environmental interactions.
c. The alleles have an additive effect on the phenotype.
d. They are continuous traits
28. Polygenic traits
a. are discrete
b. have a continuous range of expression
c. are controlled by only one genetic locus
d. include the ABO blood type system and cystic fibrosis
29. What does each mitochondrion contain?
a. nuclear DNA
b. 46 chromosomes
c. an X but never a Y chromosome
d. several copies of a ring-shaped DNA molecule, or chromosome
30. Evolution can be described as a two-stage process that includes which of the following?
a. genetic drift followed by migration
b. natural selection followed by migration
c. recombination followed by mutation
d. production of variation followed by natural selection acting on this variation
31. Evolution can be most succinctly defined as
a. the appearance of new species
b. the change from one species to another in one generation
c. the change in allele frequency from one generation to the next
d. any type of genetic mutation
32. What is the only source of new genetic material in any population?
a. mutation
b. genetic drift
c. founder effect
d. migration
33. What produces new alleles at a locus?
a. natural selection
b. recombination
c. mutation
d. migration
34. In order for a mutation to be passed on to offspring, the mutation must
a. occur in a gamete
b. be beneficial
c. occur in a somatic cell
d. result in additional chromosomes
35. What is gene flow defined as?
a. production of new alleles
b. production of new genetic material
c. chance loss of alleles in a population
d. exchange of genes between populations
36. Genetic drift is
a. the change in allele frequencies produced by random factors
b. the result of large populations
c. the opposite of founder effect
d. not evolutionary change
37. Which of the statements below is false regarding the relationship between malaria and the HbS
allele?
a. There is no geographic correlation between the distribution of the HbS allele and malaria.
b. Heterozygotes have greater resistance to malaria than homozygous individuals.
c. The malarial parasite does not reproduce very well in the red blood cells of heterozygotes.
d. Malaria is caused by the Plasmodium parasite.
38. The HbS allele increased in frequency in West African populations due to which of the following?
a. sickle-cell anemia
b. genetic drift
c. migration
d. increased mutation rates
3. Dominance and recessiveness are all-or-nothing situations because the recessive allele has no
5. Polygenic traits account for few, if any, of the readily observable phenotypic variation seen in
6. The genotype sets limits and potentials for development and interacts with the environment to
7. Mitochondrial DNA (mtDNA) is extremely useful for studying genetic change over time.
8. New alleles are the results of mutations.
9. Genetic drift is the random factor in evolution.
10. The relationship between malaria and the HbS allele is an example of natural selection as a factor that
11. A manifestation of sickle-cell anemia is the abnormal hemoglobin S reduces the ability of red blood
12. In regions where malaria is present, it acts as a selective agent that favors the heterozygous
phenotype, because people with sickle-cell trait produce more offspring than those with only normal
2. Explain Mendel’s principle of independent assortment.
3. What are the typical Mendelian phenotypic and genotypic ratios in the F2 generation for a cross of
5. Explain why a woman with type O blood and a man with type A blood could potentially have
6. Explain how two parents who do NOT express a particular trait in their phenotype can nevertheless
produce children who express the trait. Give an example of a specific trait or disease where this could
7. Define genetic drift. How are founder effect and genetic drift related?
9. What is meant by the statement, “natural selection is the one factor that can cause directional change
1. Why is mutation an important element in accounting for the variation in mtDNA? What are the
factors that redistribute genetic variation?
2. Using the HbS allele to illustrate, describe why fitness levels are a function of the environment.
3. Discuss the differences between Mendelian and polygenic modes of inheritance. Provide an example
of a Mendelian and a polygenic trait.
4. Allele frequencies are indicators of the genetic makeup of a population. Use the example of ABO