Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
A clade is a group of organisms that have evolved from a common ancestor, including all its .
Evidence for which species are part of a clade can be obtained from the base sequences of a gene or the corresponding amino acid sequence of a protein.
Sequence differences accumulate gradually; therefore, there is a positive correlation between the number of differences between two species and the time since they diverged from a common ancestor. This principle is known as the molecular clock.
Traits are classified as homologous if they are similar due to common ancestry (e.g., the pentadactyl limb), or analogous if they are similar due to convergent evolution (e.g., the wings of a and a ).
Cladograms are tree diagrams that show the most probable sequence of divergence in clades based on the principle of parsimony.
Evidence from cladistics has shown that classifications of some groups based on morphology did not correspond with evolutionary origins, leading to reclassifications (e.g., the reclassification of the family ).
📐Formulae
💡Examples
Problem 1:
Two species of primates have a genetic difference of in a specific non-coding DNA sequence. If the estimated mutation rate () for this sequence is per million years, calculate the time () since these two species shared a common ancestor.
Solution:
Explanation:
Using the molecular clock formula, the time since divergence is calculated by dividing the total genetic distance by the rate of mutation per million years.
Problem 2:
A sequence of amino acids is compared between a human and a chimpanzee. Only amino acids are found to be different. Calculate the percentage divergence.
Solution:
Explanation:
The percentage divergence is the number of differences () divided by the total number of units in the sequence (), multiplied by to get the percentage.