Molecular Clocks, Evolutionary Timing, and Applications

What is the purpose of a molecular clock?

To estimate the time of evolutionary divergence between species using DNA mutation rates.

How is a molecular clock calibrated?

By using fossil evidence or known evolutionary events to set reference points for mutation rates.

What assumption does the molecular clock method rely on?

That genetic changes accumulate at a relatively constant rate over time.

Why do molecular clocks differ between genes?

Because mutation rates vary depending on the gene’s function and selective pressure.

Which genes evolve faster — essential or nonessential ones?

Nonessential genes evolve faster because mutations are less likely to be harmful.

What type of DNA is often used for studying recent evolutionary events?

Mitochondrial DNA (mtDNA), which evolves rapidly and is maternally inherited.

What type of DNA is used for studying ancient divergences?

Ribosomal RNA (rRNA) genes, because they evolve slowly.

How can molecular clocks help link fossil and genetic data?

They bridge the gap by estimating divergence times even when the fossil record is incomplete.

What can cause molecular clocks to be inaccurate?

Natural selection, varying mutation rates, or horizontal gene transfer.

What is horizontal gene transfer (HGT)?

The movement of genes between different species rather than by vertical inheritance.

How does HGT complicate phylogenetic trees?

It can make unrelated organisms appear more closely related.

What early-life phenomenon may have caused extensive HGT?

The fusion of early cells and gene sharing among ancient prokaryotes.

What does the tree of life often resemble when considering HGT?

A network or web rather than a simple branching tree.

Why is phylogeny useful in biology?

It helps understand evolutionary relationships, trace the origins of traits, and classify organisms based on ancestry rather than appearance.

How do phylogenetic trees assist in medicine?

They help identify disease origins, track pathogen evolution, and develop vaccines by comparing genetic sequences.

How can phylogeny be used in conservation biology?

To identify evolutionarily distinct lineages worth protecting and guide conservation priorities.

What is the three-domain system?

A classification dividing life into Bacteria, Archaea, and Eukarya based on molecular data.

Who proposed the three-domain system?

Carl Woese and colleagues.

What molecular evidence led to the three-domain system?

rRNA sequence comparisons showing that Archaea are more closely related to Eukarya than to Bacteria.

What are the three domains of life?

Bacteria, Archaea, and Eukarya.

What are Bacteria characterized by?

Prokaryotic cells with peptidoglycan cell walls and unique RNA polymerases.

What are Archaea characterized by?

Prokaryotic cells without peptidoglycan, and unique membrane lipids and rRNA genes.

What are Eukarya characterized by?

Eukaryotic cells with nuclei and membrane-bound organelles.

Why is the domain Archaea unique?

It includes many extremophiles but also species found in moderate environments.

What does the three-domain system reveal about the origin of eukaryotes?

That eukaryotes share a more recent common ancestor with Archaea than with Bacteria.

Why is the “Tree of Life” not perfectly branching?

Because horizontal gene transfer has occurred between lineages over evolutionary time.

How does horizontal gene transfer affect classification?

It blurs evolutionary boundaries, making relationships more network-like.

What modern approach helps clarify evolutionary relationships?

Genome sequencing and bioinformatics for comparing whole genomes.

What does the “web of life” model emphasize?

The complex, interconnected nature of early evolution due to gene transfer between domains.

What is the main takeaway of the Tree of Life concept?

All organisms are connected by shared ancestry through evolution, despite immense diversity.