Gold ions ( $\mathrm{Au}^{3+}$ ) are toxic to most microorganisms. However, the bacterium Delftia acidovorans is frequently found in sticky layers, called biofilms, that form on the surface of gold deposits.
D. acidovorans produces a peptide synthase that catalyses the synthesis of a small peptide called delftibactin. When isolated, delftibactin can precipitate $\mathrm{Au}^{3+}$ ions as small particles of metallic gold. Delftibactin is a secondary metabolite.

The patty pan squash plant, Cucurbita pepo, produces edible fruits that vary in colour.

The summer squash plant, Cucurbita pepo, produces edible fruits that vary in shape. Fig. 2.1 shows the fruits of three different varieties of squash plants.

Fruit shape in squashes is controlled by two genes, A / a and B / b, that are located on different chromosomes.
- A disc-shaped fruit is produced when both dominant alleles, A and B, are present.
- A spherical fruit is produced when either allele A or allele B is present, but not if both A and B are present.
- A long fruit is produced when both allele A and allele B are absent.

The pink bollworm moth, Pectinophora gossypiella, is a pest of cotton crops. The size of its population can be reduced by releasing large numbers of sterile male moths into cotton fields. The sterile male moths mate with wild females from the cotton fields, but no offspring are produced.

Over a period of three years, 20 million genetically modified (GM) sterile male moths were released in the USA. Each insect contained a gene coding for a red fluorescent protein (DsRed) taken from a species of reef coral. The added DNA also included a promoter.

Domestic goats are small, herbivorous animals that provide milk for human use. This is an important source of food for people in rural South Africa.

Three Northern European goat varieties (breeds) have been imported to South Africa because they have higher milk yields than the native South African goats.

Table 2.1 compares the mean daily milk yields of these three breeds of Northern European goat in three locations, Northern Europe, Barbados and South Africa.

Domestic goats are small, herbivorous animals that provide milk for human use. Goats' milk is an important source of food for people living in rural China. Xinong Saanen and Guanzhong are the names of two varieties (breeds) of goat common in China.

In these breeds, there is genetic variation at nucleotide position 5752 of a gene coding for a growth factor. At this position there is either a cytosine (C) or a guanine (G) nucleotide. Some individuals are homozygous for the allele containing C at this position (CC), some are homozygous for the allele containing G at this position (GG) and some are heterozygous (CG).

Table 2.1 compares the mean milk yield of the first milk-producing period (first lactation) and the next milk-producing period (second lactation) for Xinong Saanen goats of each genotype.