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Essentials of Genetics

William S. Klug, Michael R. Cummings, Charlotte A. Spencer

Chapter 21

Population and Evolutionary Genetics - all with Video Answers

Educators

Chapter Questions

00:54

Problem 1

HOW DO WE KNOW? Population geneticists study changes in the nature and amount of genetic variation in populations, the distribution of different genotypes, and how forces such as selection and drift act on genetic variation to bring about evolutionary change in populations and the formation of new species. From the explanation given in the chapter, what answers would you propose to the following fundamental questions?
(a) How do we know how much genetic variation is in a population?
(b) How do geneticists detect the presence of genetic variation as different alleles in a population?
(c) How do we know whether the genetic structure of a population is static or dynamic?
(d) How do we know when populations have diverged to the point that they form two different species?
(e) How do we know the age of the last common ancestor shared by two species?

Grant Castaneda
Grant Castaneda
Numerade Educator
03:38

Problem 2

CONCEPT QUESTION Read the Chapter Concepts liston page 412 All these pertain to the principles of population genetics and the evolution of species. Write a short essay describing the roles of mutation, migration, and selection in bringing about speciation.

Bryan Lynn
Bryan Lynn
Numerade Educator
06:16

Problem 3

Price et al. $[(1999) . \text { J. Bacteriol. } 181: 2358-2362]$ conducted a genetic study of the toxin transport protein (PA) of Bacillus anthracis, the bacterium that causes anthrax in humans. Within
the 2294 -nucleotide gene in 26 strains they identified five point mutations-two missense and three synonyms-among different isolates. Necropsy samples from an anthrax outbreak in 1979
revealed a novel missense mutation and five unique nucleotide changes among ten victims. The authors concluded that these data indicate little or no horizontal transfer between different
B. anthracis strains.
(a) Which types of nucleotide changes (missense or synonyms) cause amino acid changes?
(b) What is meant by "horizontal transfer"?
(c) On what basis did the authors conclude that evidence of
horizontal transfer is absent from their data?

Sana Riaz
Sana Riaz
Numerade Educator
00:49

Problem 4

The genetic difference between two Drosophila species, $D$. heteroneura and $D$. silvestris, as measured by nucleotide diversity, is about 1.8 percent. The difference between chimpanzees $($Pan troglodytes ) and humans (H. sapiens) is about the same, yet the latter species is classified in a different genera. In your opinion, is this valid? Explain why.

Joanna Quigley
Joanna Quigley
Numerade Educator
03:09

Problem 5

The use of nucleotide sequence data to measure genetic variability is complicated by the fact that the genes of many eukaryotes are complex in organization and contain $5^{\prime}$ and $3^{\prime}$ flanking regions as well as introns. Researchers have compared the nucleotidesequenceoftwoclonedallelesofthe $\gamma$ -globingenefroma single individual and found a variation of 1 percent. Those differences include 13 substitutions of one nucleotide for another and three short DNA segments that have been inserted in one allele or deleted in the other. None of the changes takes place in the gene's exons (coding regions). Why do you think this is so, and should it change our concept of genetic variation?

Khalida Dawar
Khalida Dawar
Numerade Educator
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Problem 6

Consider rare disorders in a population caused by an autosomal recessive mutation. From the frequencies of the disorder in the population given, calculate the percentage of heterozygous carriers:
(a) 0.0064
(b) 0.000081
(c) 0.09
(d) 0.01
(e) 0.10

Ronald Prasad
Ronald Prasad
Numerade Educator
02:23

Problem 7

What must be assumed in order to validate the answers in Problem $6 ?$

Jacquelyn Trost
Jacquelyn Trost
Numerade Educator
02:19

Problem 8

In a population where only the total number of individuals wit the dominant phenotype is known, how can you calculate th percentage of carriers and homozygous recessives?

Khalida Dawar
Khalida Dawar
Numerade Educator
01:18

Problem 9

If 4 percent of a population in equilibrium expresses a recessive trait, what is the probability that the offspring of two individuals who do not express the trait will express it?

Anand Jangid
Anand Jangid
Numerade Educator
05:16

Problem 10

ConsiderapopulationinwhichthefrequencyofalleleAisp $=0.7$ and thefrequencyofalleleais $q=0.3$, andwheretheallelesarecodominant. What will be the allele frequencies after one generation if the following occurs?
(a) $w_{A A}=1, w_{A a}=0.9, w_{a a}=0.8$
(b) $w_{A A}=1, w_{A a}=0.95, w_{a a}=0.9$
(c) $w_{A A}=1, w_{A a}=0.99, w_{a a}=0.98$
(d) $w_{A A}=0.8, w_{A a}=1, w_{a a}=0.8$

John Barone
John Barone
Numerade Educator
02:06

Problem 11

Iftheinitialallelefrequenciesarep $=0.5$ and $q=0.5$ andallelecisalethal recessive, what will be the frequencies after $1,5,10,25,100,$ and 1000 generations?

Hailey Tomashek
Hailey Tomashek
Numerade Educator
01:47

Problem 12

Under what circumstances might a lethal dominant allele persist in a population? Assume that a recessive autosomal disorder occurs in 1 of 10,000

Danielle Ashley
Danielle Ashley
Numerade Educator
01:44

Problem 13

Assume that a recessive autosomal disorder occurs in 1 of 10,000 individuals (0.0001) in the general population and that in this population about 2 percent (0.02) of the individuals are carriers for the disorder. Estimate the probability of this disorder occurring in the offspring of a marriage between first cousins. Compare this probability to the population at large.

Dominador Tan
Dominador Tan
Numerade Educator
09:43

Problem 14

One of the first Mendelian traits identified in humans was a dominant condition known as brachydactyly. This gene causes an abnormal shortening of the fingers or toes (or both). At the time, some researchers thought that the dominant trait would spread until 75 percent of the population would be affected (because the phenotypic ratio of dominant to recessive is 3: 1 ). Show that the reasoning was incorrect.

Bryan Valdivia
Bryan Valdivia
Numerade Educator
01:45

Problem 15

Describe how populations with substantial genetic differences can form. What is the role of natural selection?

Aditya Sood
Aditya Sood
Numerade Educator
03:38

Problem 16

Achondroplasia is a dominant trait that causes a characteristic form of dwarfism. In a survey of 50,000 births, five infants with achondroplasia were identified. Three of these infants had par-
ents with achondroplasia, while two did not. Calculate the mutation rate for achondroplasia, and express the rate as the number of mutant genes per given number of gametes.

Khalida Dawar
Khalida Dawar
Numerade Educator
02:23

Problem 17

A recent study examining the mutation rates of 5669 mammalian genes $(17,208$ sequences) indicates that, contrary to popular belief, mutation rates among lineages with vastly different generation lengths and physiological attributes are remarkably constant [Kumar, S., and Subramanian, S. $(2002) .$ Proc. Natl. Acad. Sci.USA99:803-808|.Theaveragerateisestimatedat12.2 $\times 10^{-9}$ perbp per year. What is the significance of this finding in terms of mammalian evolution?

Nimi Das
Nimi Das
Numerade Educator
00:18

Problem 18

What are considered significant factors in maintaining the surprisingly high levels of genetic variation in natural populations?

Sisi Gao
Sisi Gao
Numerade Educator
02:27

Problem 19

A botanist studying water lilies in an isolated pond observed three leaf shapes in the population: round, arrowhead, and scalloped. Marker analysis of DNA from 125 individuals showed the round-leaf plants to be homozygous for allele $r 1$, while the plants with arrowhead leaves were homozygous for a different allele at the same locus, $r 2 .$ Plants with scalloped leaves showed DNA profiles with both the $r 1$ and $r 2$ alleles. Frequency of the $r 1$ allele was estimated at $0.81 .$ If the botanist counted 20 plants with scalloped leaves in the pond, what is the inbreeding coefficient $F$ for this population?

Joanna Quigley
Joanna Quigley
Numerade Educator
03:00

Problem 20

A farmer plants transgenic Bt corn that is genetically modified to produce its own insecticide. Of the corn borer larvae feeding on these Bt crop plants, only 10 percent survive unless they have at least one copy of the dominant resistance allele $B$ that confers resistance to the Bt insecticide. When the farmer first plants Bt
corn, the frequency of the $B$ resistance allele in the corn borer population is $0.02 .$ What will be the frequency of the resistance allele after one generation of corn borers have fed on Bt corn?

Hailey Tomashek
Hailey Tomashek
Numerade Educator
03:48

Problem 21

In an isolated population of 50 desert bighorn sheep, a mutant recessive allele $c$ when homozygous causes curled coats in both males and females. The normal dominant allele $C$ produces straight coats. A biologist studying these sheep counts four with curled coats. She also takes blood samples from the population for DNA analysis, which reveals that 17 of the sheep are heterozygous carriers of the $c$ allele. What is the inbreeding coefficient $F$ for this population?

John Barone
John Barone
Numerade Educator
02:06

Problem 22

To increase genetic diversity in the bighorn sheep population described in Problem 21 , ten sheep are introduced from a population where the $c$ allele is absent. Assuming that random mating occurs between the original and the introduced sheep, and that the $c$ allele is selectively neutral, what will be the frequency of $c$ in the next generation?

Hailey Tomashek
Hailey Tomashek
Numerade Educator
01:33

Problem 23

What genetic changes take place during speciation? Some critics have warned that the use of gene therapy

Nimi Das
Nimi Das
Numerade Educator
01:55

Problem 24

Some critics have warned that the use of gene therapy to correct genetic disorders will affect the course of human evolution. Evaluate this criticism in light of what you know about population genetics and evolution, distinguishing between somatic gene therapy and germ-line gene therapy.

Khalida Dawar
Khalida Dawar
Numerade Educator
01:01

Problem 25

List the barriers that prevent interbreeding, and give an example of each.

Joanna Quigley
Joanna Quigley
Numerade Educator
04:12

Problem 26

What are the two groups of reproductive isolating mechanisms? Which of these is regarded as more efficient, and why?

Camilla Martin
Camilla Martin
Numerade Educator
03:32

Problem 27

A form of dwarfism known as Ellis-van Creveld syndrome was first discovered in the late 1930 s, when Richard Ellis and simon van Creveld shared a train compartment on the way to a pediatrics meeting. In the course of conversation, they discovered that they each had a patient with this syndrome. They published a description of the syndrome in $1940 .$ Individuals with this syndrome have a short-limbed form of dwarfism and often have defects of the lips and teeth, and polydactyly (extra fingers). The largest pedigree for the condition was reported in an Old Order Amish population in eastern Pennsylvania by Victor McKusick and his colleagues $(1964) .$ In that population of $8000,$ the observed frequency is
2 per $1000 .$ In all cases, parents of children with the syndrome were unaffected, and all cases can be traced to Samuel King and
his wife, who arrived in the area in $1774 .$ It is known that neither
King nor his wife was affected with the disorder. There are no cases of the disorder in other Amish communities, such as those in Ohio or Indiana.
(a) From the information provided, derive the most likely mode of inheritance of this disorder. Using the Hardy-Weinberg law, calculate the frequency of the mutant allele in the population and the frequency of heterozygotes, assuming Hardy-Weinberg conditions.
(b) What is the most likely explanation for the high frequency of the disorder in the Pennsylvania Amish community and its absence in other Amish communities?

Sana Riaz
Sana Riaz
Numerade Educator
02:39

Problem 28

The original source of new alleles, upon which selection operates, is mutation, a random event that occurs without regard to selectional value in the organism. Although many model organisms have been used to study mutational events in populations, some investigators have developed abiotic molecular models. Soll et al. (2006. Genetics 175:267-275) examined one such model to study the relationship between both deleterious and advantageous mutations and population size in a ligase molecule composed of RNA (a ribozyme). Soll found that the smaller the population of molecules, the more likely it was that not only deleterious mutations but also advantageous mutations would disappear. Why would population size influence the survival of both types of mutations (deleterious and advantageous) in populations?

Carlene Jimenez
Carlene Jimenez
Numerade Educator
01:44

Problem 29

A number of comparisons of nucleotide sequences among hominids and rodents indicate that inbreeding may have occurred more often in hominid than in rodent ancestry. Bakewell et al. (2007. Proc. Nat. Acad. Sci. IUSAJ 104: 7489-7494) suggest that an ancient population bottleneck that left approximately 10,000 humans might have caused early humans to have a greater chance of genetic disease. Why would a population bottleneck influence the frequency of genetic disease? Shown below are two homologous lengths of the alpha and beta chains of human hemoglobin. Consult a genetic code dictionary (Figure 12.7 ), and determine how many amino acid substitutions may have occurred as a result of a single nucleotide substitution. For any that cannot occur as a result of a single change, determine the minimal mutational distance.

Josee Pacheco
Josee Pacheco
Numerade Educator
04:30

Problem 30

Shown below are two homologous lengths of the alpha and beta chains of human hemoglobin. Consult a genetic code dictionary (Figure 12.7 ), and determine how many amino acid substitutions may have occurred as a result of a single nucleotide substitution. For any that cannot occur as a result of a single change, determine the minimal mutational distance.

Jessica Honkomp
Jessica Honkomp
Numerade Educator
09:24

Problem 31

Recent reconstructions of evolutionary history are often dependent on assigning divergence in terms of changes in amino acid or nucleotide sequences. For example, a comparison of cytochrome
c shows 10 amino acid differences between humans and dogs, 24 differences between humans and moths, and 38 differences between humans and yeast. Such data provide no information as to the absolute times of divergence for humans, dogs, moths, and yeast. How might one calibrate the molecular clock to an absolute time clock? What problems might one encounter in such a calibration?

April Townson
April Townson
Numerade Educator