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?

Step by step solution

01

Question (a): Types of nucleotide changes causing amino acid changes

Missense mutations are the type of nucleotide changes that cause amino acid changes. These mutations occur when a single nucleotide change results in a codon that codes for a different amino acid. As a result, the protein's primary structure changes, which may affect its function.

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Question (b): Meaning of "horizontal transfer"

Horizontal transfer, also known as horizontal gene transfer (HGT), refers to the process by which genetic material is transferred between different species or organisms through a non-reproductive mechanism. This transfer can occur through various mechanisms such as transformation, conjugation or transduction and is different from the transfer of genetic material from parent to offspring (vertical transfer).

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Question (c): Basis for the authors' conclusion on the absence of horizontal transfer

The authors based their conclusion on the absence of horizontal transfer in their data on the observation of a limited number of point mutations and unique nucleotide changes among the different B. anthracis strains. In the case of significant horizontal transfer, one would expect a higher degree of genetic diversity and a greater number of mutations, reflecting the exchange of genetic material between strains. However, the observed mutations were minimal, suggesting that horizontal transfer is little or non-existent among these strains of B. anthracis.

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