Variation

Salmon may be genetically modified (GM) so that they make greater amounts of growth hormone, which is a protein. GM salmon altered in this way grow more quickly and reach their maximum body mass at a younger age than non-GM salmon.

Feb/March 2023

Sea blush, Pleciritis congesta, is a flowering plant found along the west coast of North America. Individual sea blush plants produce fruit that may be winged or wingless. Investigations have shown that this characteristic is controlled by one gene with two alleles: a dominant allele for winged fruit and a recessive allele for wingless fruit. Fig. 3.1 illustrates the structural contrast between the winged fruit and wingless fruit phenotypes.

May/June 2023

Warfarin is a poison used for controlling rats. A proportion of rats are resistant to warfarin and are able to survive exposure to the poison. This warfarin resistance results from a mutant dominant allele at a single gene locus. Researchers studied the brown rat population on a large island where there are no rat predators. On this island, warfarin is applied in an attempt to reduce the rat population. The researchers discovered that $40\%$ of the rat population showed resistance to warfarin.

May/June 2023

The harlequin ladybird, \emph{Harmonia axyridis}, is an insect with discontinuous variation in colour pattern and continuous variation in body size.

May/June 2024

Phenotypic variation occurs in many different forms.

May/June 2024

Scientists have investigated the genetics and evolution of the cat family, Felidae.

May/June 2025

Explain the advantages cross-pollination gives a plant species when compared with self-pollination.

Oct/Nov 2012

Describe and explain the structural features of a plant pollinated by wind.

Oct/Nov 2015

The blackcap, $\textit{Sylvia atricapilla}$, is a small songbird. It is a summer visitor to parts of northern Europe, where it breeds. Many blackcaps pass the winter (overwinter) in southern Europe, especially Spain. Because many people put out food for garden birds, some birds are able to survive the winter in the UK. Scientists compared the genetic variation between blackcaps from two forest sites in Germany, $800\,\text{km}$ apart. Both sites had birds that had overwintered in Spain and in the UK. The measurements were taken soon after the birds returned from their winter feeding grounds.

Oct/Nov 2015

Describe and explain the structural characteristics of a plant that is wind-pollinated.

Oct/Nov 2015

Fig. 3.1 depicts a male red deer, Cervus elaphus. Red deer are herbivores that browse low-growing vegetation in forests and on waste land. A summary of the wild red deer population on the western European island of Ireland includes the following points: - Red deer have been present in Ireland for at least 12000 years. - At first, red deer were able to move from the neighbouring island of Great Britain into Ireland across a land connection. - When sea levels rose at the end of the last Ice Age, this land connection disappeared, leaving the red deer on the two islands separated. - During the 1800s, the number of red deer in Ireland fell rapidly after the main food crop for the human population failed for several years in succession. - In the 1900s, the decline in red deer numbers continued because large areas of waste land were drained for agriculture. - By 1960, red deer were almost extinct in Ireland and remained only in one population, A, with 60 individuals. - Protection since then has allowed population A to rise to more than 600 red deer. - A number of new red deer populations, B, C and D, have also been founded in different parts of Ireland from animals brought in from Great Britain.

Oct/Nov 2017

Meiosis is one process that helps create genetic variation.

Oct/Nov 2018

The stickleback fish, Gasterosteus aculeatus, exists in two separate forms: a saltwater form and a freshwater form. The larger freshwater form is believed to have evolved from the smaller saltwater form. Both forms have armour plating on either side of the body. These plates are bony and contain a large amount of calcium. The ectodysplasin gene, EDA, codes for a protein that is involved in the formation of armour plates. The EDA gene has two alleles, low armour and high armour. Three main morphs of armour plating have been described: complete morph armour plating, partial morph armour plating, and low morph armour plating.

Oct/Nov 2019

The stickleback fish, Gasterosteus aculeatus, occurs in two separate forms: a saltwater form and a freshwater form. The larger freshwater form is believed to have evolved from the smaller saltwater form. Both forms carry armour plates along each side of the body. These plates are made of bone and contain a large amount of calcium. The ectodysplasin gene, EDA, codes for a protein that is involved in the formation of armour plates. The EDA gene has two alleles: low armour and high armour. Three major armour-plating morphs have been identified: complete morph armour plating, partial morph armour plating, and low morph armour plating.

Oct/Nov 2019

Domestic goats are small herbivores that supply milk for human consumption. In rural China, goats’ milk is a major food source. Xinong Saanen and Guanzhong are the names of two goat breeds that are widespread in China. Within these breeds, genetic variation occurs at nucleotide position 5752 of a gene that codes for a growth factor. At this site, the nucleotide is either cytosine (C) or guanine (G). Some goats are homozygous for the allele with C at this position (CC), some are homozygous for the allele with G at this position (GG), and some are heterozygous (CG). Table 2.1 compares the mean milk yield during the first milk-producing period (first lactation) and the following milk-producing period (second lactation) for Xinong Saanen goats of each genotype.

Oct/Nov 2020

Domestic goats are small herbivores that supply milk for people to use. In rural South Africa, this is a major food source. Three Northern European goat varieties (breeds) have been brought into South Africa because their milk output is greater than that of native South African goats. Table 2.1 compares the average daily milk yields of these three Northern European goat breeds in three places: Northern Europe, Barbados and South Africa.

Oct/Nov 2020

The genus Ipomoea contains more than 600 plant species. A number of these species are cultivated for their showy flowers, while others are grown as crop plants.

Oct/Nov 2023

The genus \textit{Ipomoea} includes more than 600 plant species. Some are cultivated for their decorative flowers, while others serve as crop plants.

Oct/Nov 2023

Variation can arise from many different sources. Natural selection decides which phenotypes are advantageous.

Oct/Nov 2024

Alleles are different versions of a gene. For instance, a gene locus may contain a dominant allele, T, and a recessive allele, t, at the same position. The proportion of each allele of a gene within a population can alter over time because of factors including selection, genetic drift and the bottleneck effect.

Oct/Nov 2025