CAIE IGCSE Biology 1.2.7 DNA Similarity & Common Ancestry

Practise linking DNA sequence similarity to the recency of common ancestry and interpreting evolutionary trees and tables.

Exam points

infer that fewer DNA base differences indicate a more recent common ancestor and closer relationship
compare sequence rows systematically to identify the least or most closely related pair
use branch points in an evolutionary tree to predict which organisms should have the most similar DNA

[Maximum number: 4]

A DNA molecule has two strands as shown in Fig. 6.1.

Fig. 6.1

(a)

The most closely related species have the fewest differences between their DNA sequences. State which two plant species shown in Table 6.1 are most distantly related to each other.

[ 1 ]

(b)

The most closely related species have the shortest distance from a branching point on a classification tree.

Use the information in Table 6.1 to complete the classification tree in Fig. 6.3. Write the letter corresponding to species B, C, D and G in the box next to the correct branch of the classification tree.

Fig. 6.3

[ 3 ]

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1.2.7—Groups of organisms which share a more question 1

Question (a)

Question (b)