Glossary
I’ve put together the following glossary of handy plant-breeding terminology. I hope you find it useful – I certainly learned a few things in the process of compiling it!
Allele: a variant of a gene at a specific locus
Annual: a plant that is born, grows & dies in a single growing season. Relatively uncommon in natural flora but the vast majority of human food crops are annuals. Why? Well that’s something we can debate! Annuals are always propagated from seed.
Backcross: a cross between the product of a cross and one of the original parent plants. See also recurrent backcross.
Biennial: a plant that is born in one growing season, overwinters, and then sets seed in the next growing season. Always propagated from seed.
Breed true: when a plant’s seeds produce offspring that resemble the parent plant
Chromosome: the structures inside cell nuclei that carry the genes
Codominance: when the different alleles on a given gene loci co-determine the phenotype, rather than expressing dominant or recessive characteristics
Cross: sexual reproduction between two different parents
Dioecious: types of plant where the male & female flowers occur on different individual plants.
Dominance: an allele which expresses itself in the plant phenotype even if there is another allele at the gene locus
F1: in general, a term referring to the first generation after a cross (F1 = ‘first filial generation’). Used to refer more specifically to ‘F1 hybrids’, when two different varieties of a plant are crossed.
GM: genetic modification, using biotechnological techniques to manipulate the plants genome directly rather than indirectly, as in traditional plant breeding. See my rant.
Gene: the building blocks of inheritance - sections of DNA which act as ‘recipes’ for making specific proteins
Gene linkage: genes are linked when they’re on the same chromosome – this can be significant in plant breeding because it affects the degree of recombination, and hence variation, in the offspring
Genotype: the specific genes possessed by a plant
Hand pollination: pollinating a plant by (the gardener’s) hand, to ensure that the seed is produced by the desired parents
Heirloom: an old, open-pollinated vegetable variety, usually handed down between amateur gardeners
Heterozygous: a plant with two different alleles at a specific gene locus
Homozygous: a plant with two identical alleles at a specific gene locus
Hybrid: a cross between different varieties of a plant
Hybrid vigour: the situation when a hybrid plant displays a superior trait or traits compared to the parent plants.
Inbreeder: a plant that is self-fertile and tends to pollinate itself
Inbreeding depression: loss of vigour in plants with closely-related parents. Can be a problem with outbreeders.
Locus: the position on a chromosome occupied by a specific gene
Monoecious: plants that have separate male and female flowers on each individual plant
Outbreeder: a plant variety that tends to cross with other plants of its kind rather than self-pollinating
Perennial: a plant that lives through several growing seasons. Can generally reproduce vegetatively instead of or as well as by seed.
Perfect flower: or ‘synoecious’ (as compared to monoecious or dioecious) – a plant whose flowers contain both male & female reproductive structures.
Phenotype: what a plant is like, which depends upon its genotype and other (environmental) factors
Ploidy: OK, time to get the biology textbook out. Animal & plant sex cells contain only one set of chromosomes, and are called ‘haploid’. When the male & female cells fuse to make an embryo, its cells have two sets of chromosomes, and are called ‘diploid’. Dumb, primitive critters like us mammals are only ever diploid, but in plants (particularly a lot of cultivated ones) the chromosomes can divide as if the cell itself is about to divide, but then fail to do so, leading to four pairs of chromosomes – a tetraploid cell. You can also get octoploid cells, or even odd numbered ones like triploid cells. In cultivated varieties, these polyploid cells can originate from different plants. For example, wheat is – oh my goodness me – an allohexaploid plant with three distinct genomes. Why does all this matter for plant breeders? Firstly because polyploidy often leads to traits that we want in our vegetables, such as larger fruit and leaves. But it can also lead to genetic instabilities which mean we can’t usually propagate the polyploid from seed – hence things like apple trees, bananas, and potatoes which are usually propagated vegetatively. So, plant breeders, when playing with polyploid plants please proceed with precision!
Pollination: plant sex, in which the male sex cells (the pollen) fuse with the female sex cells (the ovule), ultimately to form a seed.
Recessive: the opposite of dominant, an allele that does not express itself in the plant phenotype if there is a dominant allele at the locus
Recurrent Backcrossing: a plant breeding technique in which repeated backcrosses isolate a desired trait from a given variety and transfer it back to an original variety.
Recombination: the situation in which the offspring of a cross don’t just replicate the traits of the parents, thereby providing us with the possibility of breeding new plant varieties.
Selection: choosing which individual plants to perpetuate by breeding
Self-pollination: the extreme case of inbreeding, in which an individual plant has sex with itself
Self-incompatibility: the tendency of plants to limit inbreeding by preventing self-pollination by various mechanisms
Variable expressivity: the situation in which a genotype is not necessarily reflected in identical phenotypes even given the same environment
Vegetative reproduction: non-sexual reproduction, involving propagation from tubers, divisions, root cuttings etc in which the new plant is usually a clone (genetically identical) to the parent |
