Generation of Variation

Ch. 12 part 1 p. 325-323, part 2 p. 343-353

What is the definition of mutation, and why is it considered the ultimate source of evolution?

A heritable change in genetic information; without mutation, there would be no evolution.

What process can be considered an expansion of "mutation" since it also mixes genetic material?

Recombination — the mixing of genetic material between different lineages.

What are the five main sources of mutation?

Errors in replication, errors in segregation, transposition, DNA damage, and aberrant homologous recombination.

What is a point mutation?

A change of one base pair to another at a single position in the DNA sequence.

What defines insertions and deletions, and what are smaller ones called?

Daughter DNA has a different number of bases than parental DNA (ranging from one base to thousands of genes); smaller ones are called "indels."

What is tandem duplication, and where does the inserted sequence typically come from?

Most insertions aren't random — the inserted sequence is typically copied or moved from elsewhere in the cell. If copied, this creates two or more instances of the sequence in the genome, termed duplication.

How does the DNA polymerase error rate compare to the final organismal mutation rate, and why?

Polymerase error rate is much higher than the final organismal error rate, because organisms use a variety of protection, prevention, and correction mechanisms to limit the effect of mutations.

What is the human mutation rate, and roughly how many errors occur per diploid genome per replicative event?

About 1 error per 10,000,000,000 base positions per replicative event. With a haploid genome size of ~3,100,000,000, that's less than 1 error (~0.6) per diploid genome.

What are the three repair processes listed under "Protection, Prevention, Correction"?

Direct repair, excision repair, and recombinational repair.

What example of physical protection against mutation is common among organisms, and what pathway illustrates this?

Pigmentation. The delayed tanning pathway: UV radiation causes keratinocyte DNA damage and p53 expression, leading to POMC transcription. POMC processing produces α-MSH and β-endorphins; α-MSH binds MC1R on melanocytes, triggering MITF expression and melanogenesis (tanning). β-endorphin (a byproduct of POMC cleavage) can influence tanning addiction.

What is transposition, and what are the mobile DNA elements involved called?

The movement within the genome of mobile DNA elements, known as transposable elements or transposons.

According to the notes, what is the evolutionary origin of transposons/transposable elements?

Viruses are the source of transposons/transposable elements.

What is true about most transposable elements in humans, and where do they occur more frequently?

Most are inactive, and they occur more frequently near the centromere of chromosomes.