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Chapter 22: Problem 3

Price et al. (1999. 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?

Short Answer

Expert verified
Answer: Missense mutations cause amino acid changes in proteins, whereas synonyms do not. The difference between these two types of mutations is that a missense mutation is a change in a single nucleotide that results in a different amino acid being incorporated into a protein, altering its function, while a synonym mutation is a change in a single nucleotide that does not affect the amino acid produced due to the flexibility of the genetic code allowing some amino acids to be encoded by more than one codon.

Step by step solution

01

(a) Types of Nucleotide Changes

(A nucleotide change can be either missense or synonym. A missense mutation is a change in a single nucleotide that results in a different amino acid being incorporated into a protein, thereby altering its function. In contrast, a synonym mutation is a change in a single nucleotide that does not affect the amino acid produced, because some amino acids can be encoded by more than one codon. Therefore, missense mutations cause amino acid changes, while synonyms do not.)
02

(b) Horizontal Transfer Definition

(Horizontal transfer, also known as lateral transfer, refers to the transfer of genetic material between organisms in a method that is not directly inherited from a parent or ancestor. This can occur through mechanisms such as conjugation, transformation, or transduction. It results in the acquisition of new traits or genes in an organism, which can lead to increased genetic variety and the possibility for adaptation in populations.)
03

(c) Absence of Evidence for Horizontal Transfer

(The authors concluded that there was little or no evidence of horizontal transfer in their data based on the low amount of genetic variation observed among the different strains of Bacillus anthracis. They identified only five point mutations (two missense and three synonyms) in the 2294-nucleotide gene across 26 strains, and a novel missense mutation along with five unique nucleotide changes among ten victims of an anthrax outbreak. This low level of genetic diversity suggests that the strains are not frequently exchanging genetic material through horizontal transfer mechanisms, as higher genetic diversity would be expected if horizontal transfer were common.)

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Most popular questions from this chapter

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

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 \(1940 .\) Affected individuals 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 community, about 5 per 1000 births are affected, and in the population of \(8000,\) the observed frequency is 2 per \(1000 .\) All affected individuals have unaffected parents, and all affected cases can trace their ancestry 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?

In a population of cattle, the following color distribution was noted: \(36 \%\) red \((R R), 48 \%\) roan \((R r),\) and \(16 \%\) white \((r r) .\) Is this population in a Hardy-Weinberg equilibrium? What will be the distribution of genotypes in the next generation if the HardyWeinberg assumptions are met?

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?

In a population of 10,000 individuals, where 3600 are \(M M\) 1600 are \(N N,\) and 4800 are \(M N,\) what are the frequencies of the \(M\) alleles and the \(N\) alleles?
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