Variation and Natural Selection: Answers

What is meant by the term ‘mutation’?

A mutation is a change in a DNA sequence.

Explain why some mutations have no effect on the organism.

Some codons (groups of three DNA bases) code for the same amino acid. This means that sometimes when one nucleotide mutates into another (for example, if adenine changes to guanine), it will still code for the same amino acid so the protein formed will be unchanged.

Explain how Darwin’s theory of natural selection can explain the increase in the length of giraffes’ neck over time.

Within the population of giraffes, there is variation in the length of their necks. The giraffes with longer necks are more likely to survive, as they will be better able to feed on the taller trees. These giraffes are more likely to live until reproductive age, so they are more likely to reproduce and pass on their alleles for tall necks onto their offspring. Over time, this results in a gradual increase in neck length in the population.

Explain how antibiotic resistance occurs using Darwin’s theory of natural selection.

A mutation in a bacteria results in the bacteria being resistant to a particular antibiotic (such as penicillin). If bacteria are exposed to the antibiotic, then all of the bacteria will be killed except the resistant bacteria. The resistant bacteria then reproduces, forming a new population of resistant bacteria.

Why is antibiotic resistance a problem?

Antibiotic resistance is a problem because we may run out of antibiotics to treat bacterial infections. Left untreated, bacterial infections can be deadly. This is why it is so important not to use antibiotics unnecessarily and to finish the whole course of antibiotics when we do use them.