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Ch. 21 - Population and Evolutionary Genetics
Klug - Essentials of Genetics 10th Edition
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Tutti i libri di testoKlug 10th EditionCh. 21 - Population and Evolutionary GeneticsProblema 1e
Capitolo 21, Problema 1e

How do we know the age of the last common ancestor shared by two species?

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Understand that the age of the last common ancestor (LCA) shared by two species is estimated using molecular data and fossil records, which provide information about evolutionary divergence times.
Collect genetic sequence data (such as DNA, RNA, or protein sequences) from both species to compare their similarities and differences.
Calculate the genetic distance between the two species by determining the number of molecular changes or mutations that have accumulated since their divergence.
Use a molecular clock model, which assumes a relatively constant rate of genetic mutations over time, to convert the genetic distance into an estimate of divergence time. The basic formula is: \[\text{Divergence Time} = \frac{\text{Genetic Distance}}{2 \times \text{Mutation Rate}}\] where the factor 2 accounts for mutations accumulating independently in both lineages.
Calibrate the molecular clock using fossil evidence or known geological events to improve the accuracy of the estimated age of the last common ancestor.

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Molecular Clock

The molecular clock is a method that estimates the time of divergence between species by measuring the number of genetic mutations accumulated over time. It assumes mutations occur at a relatively constant rate, allowing scientists to infer the age of the last common ancestor based on genetic differences.
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Phylogenetic Trees

Phylogenetic trees are diagrams that depict evolutionary relationships among species based on genetic or morphological data. By analyzing branching patterns and genetic distances, researchers can identify common ancestors and estimate when species diverged from one another.
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Phylogenetic Trees

Fossil Record and Calibration

The fossil record provides physical evidence of past organisms and helps calibrate molecular clocks by offering minimum age estimates for divergence events. Combining fossil data with genetic information improves accuracy in dating the last common ancestor of species.
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Domanda del libro di testo

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.

Which types of nucleotide changes (missense or synonyms) cause amino acid changes?

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How do we know when populations have diverged to the point that they form two different species?

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Domanda del libro di testo

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.

What is meant by 'horizontal transfer'?

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Domanda del libro di testo

Write a short essay describing the roles of mutation, migration, and selection in bringing about speciation.

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How do we know whether the genetic structure of a population is static or dynamic?

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How do geneticists detect the presence of genetic variation as different alleles in a population?

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