Explain that a mutation is a change in the DNA base sequence with harmful, beneficial, or neutral effects, and that genetic variation (from mutation and sexual reproduction) is important to the survival of a species (Virginia 2018 Biology SOL BIO.5.c).

What this topic is asking

Virginia Biology SOL standard BIO.5.c states that genetic variation is important to the survival of a species. To understand this you need to know what a mutation is, that mutations can be harmful, beneficial, or neutral, the difference between mutations in body cells and in gametes, and how variation arises from mutation and sexual reproduction. The Biology EOC connects this directly to natural selection and evolution, so it is a bridge between the genetics and evolution modules.

What a mutation is

Mutations are the ultimate source of all new genetic information. Without mutation there would be no new alleles, and life could not change over time. The EOC expects you to connect a change in the DNA to a possible change in the protein and the trait.

Harmful, beneficial, or neutral

It is a mistake to assume mutations are always bad. Many are neutral, some are beneficial, and a mutation that is harmful in one environment can be helpful in another. Beneficial mutations are the source of the advantageous traits that natural selection acts on.

Body-cell versus gamete mutations

Where a mutation happens determines whether it is inherited:

• A mutation in a gamete (egg or sperm) can be passed to offspring and so enters the next generation; these are the mutations that matter for evolution.
• A mutation in a body cell (somatic cell) affects only that individual and is not passed on; for example, a skin-cell mutation from sun damage is not inherited.

The EOC may ask which kind of mutation can be inherited; the answer is a mutation in the gametes.

Variation and the survival of a species

Genetic variation is the range of different alleles and traits in a population. It comes from mutation (the source of new alleles) and from sexual reproduction (crossing over, independent assortment, and random fertilization shuffle the alleles into new combinations, see meiosis and genetic variation). Variation matters because environments change. In a varied population, some individuals are likely to have traits suited to the new conditions, so they survive and reproduce and the species persists. A population with little variation is far more vulnerable to being wiped out by a disease or environmental change. This is exactly the raw material that natural selection acts on.

Try this

Q1. State the three possible effects of a mutation. [1]

• Cue. Harmful, beneficial, or neutral.

Q2. Explain why a mutation in a sperm cell can be inherited but a mutation in a skin cell cannot. [2]

• Cue. A sperm cell is a gamete, so its DNA can be passed to offspring at fertilization; a skin cell is a body cell, so its mutation affects only that individual and is not passed on.