Explain that groups of organisms which share a more recent ancestor (are more closely related) have base sequences in DNA that are more similar than those that share only a distant ancestor

The genetic similarity between organisms can be understood through the concept of common ancestry, which is fundamental to evolutionary biology. Groups of organisms that share a more recent common ancestor tend to have more similar base sequences in their DNA compared to those that share only a distant ancestor. Here’s a detailed explanation of this concept:

Genetic Similarity and Common Ancestry

1. Common Ancestor

• A common ancestor is an organism from which two or more species have evolved. The more recent the common ancestor, the more closely related the descendant species are expected to be. For example, humans and chimpanzees share a relatively recent common ancestor, while humans and frogs share a much more distant ancestor.

2. DNA Base Sequences

• DNA is composed of sequences of four nucleotide bases: adenine (A), thymine (T), cytosine (C), and guanine (G). The specific order of these bases encodes genetic information. When two species diverge from a common ancestor, mutations accumulate over time in their DNA sequences due to various factors such as natural selection, genetic drift, and environmental changes.

3. Evolutionary Divergence

• As species evolve and diverge from their common ancestor, their DNA sequences begin to differ. The rate at which these differences accumulate can vary among different genes and organisms. However, species that have diverged more recently will typically exhibit fewer differences in their DNA sequences compared to those that have been separated for longer periods.

4. Molecular Evidence

• Molecular biologists use techniques such as DNA sequencing to compare the genetic material of different organisms. By analyzing the similarities and differences in their base sequences, scientists can infer evolutionary relationships:
  • Closer Relationships: Species with a recent common ancestor will show high levels of similarity in their DNA sequences. For instance, humans share about 98% of their DNA with chimpanzees.
  • Distant Relationships: In contrast, species that have diverged from a common ancestor millions of years ago will show greater genetic differences. For example, the genetic similarity between humans and fish is much lower due to the long evolutionary separation.

5. Phylogenetic Analysis

• Phylogenetic trees can be constructed based on genetic data to visualize these relationships. Branch lengths in these trees often represent the amount of genetic change or divergence that has occurred since the common ancestor was shared. Shorter branches indicate closer relationships with fewer genetic differences, while longer branches suggest more distant relationships with greater genetic divergence.