Allele: An alternative form of a gene

Dominant: A dominant allele is always expressed in the phenotype when it occurs in the genotype. It masks the presence of a recessive allele.

Recessive: A recessive allele is expressed only when accompanied by another recessive.

Phenotype: The outward appearance/visible expression of the genotype if the phenotype.

Genotype: The genotype is the genetic makeup of an individual for a characteristic

Genetic crosses of single gene combinations (monohybrid inheritance) can be shown and examined using Punnett squares. These show the possible offspring combinations that could be produced, and the probability of these combinations can be calculated.

Pedigree charts show the presence or absence of a trait within a family across generations

Each species has its own characteristic number of chromosomes. Humans, for instance, have 46 chromosomes in a typical body cell (somatic cell), while dogs have 78.

Like many species of animals and plants, humans are diploid (2n), meaning that most of their chromosomes come in matched sets known as homologous pairs. The 46 chromosomes of a human cell are organized into 23 pairs.

Benefits:

• new varieties may be economical as they produce more and better quality food

• animals can be selected that cannot cause harm e.g. cattle without horns

Risks:

• reduced genetic variation can lead to attack by specific insects of disease which could be destructive

• rare disease genes can be unknowingly selected as a part of a positive trait learning with problems with organisms

• can create physical problems for organisms e.g. some breeds of dogs can have hip dysplasia due to hips not being formed correctly.

Cloning is the process of producing individual organisms with identical or virtually identical DNA, either by natural or artificial means.