An introduction to basic genetics
by Greg Green
An introduction to basic geneticsGenetics are somewhat difficult to understand at first so it is best if we give you a grounding in some of the breeding concepts mentioned in this chapter.
We will start by first explaining what a couple of words mean. These words will appear throughout this chapter so it is best to define them at this point.
Genes – Each of the units of heredity which are transmitted from parent to offspring in gametes, usually as part of a chromosome, and control or determine a single characteristic in the offspring. [There are genes responsible for each feature of your plant to be inherited, for leaf colour, stem structure, texture, smell, potency, etc.]
Alleles – Any of a number of alternative forms of one gene. [For example the Gene for purple bud colour may have 2 forms, one for purple and one for dark red.]
Homozygous – An individual that has identical alleles at one or more genetic loci, which is not a heterozygote and so breeds true. [Your plant is to be said homozygous for one feature when it carries in its responsible gene pair the same gene twice, which means both genes of the gene pair are equal.]
Heterozygous – An individual having different alleles at one or more genetic loci. [Your plant is to be said heterozygous for one feature when the genes of the responsible gene pair are unequal.]
Phenotype – An organism distinguishable from others by observable features. [How your plant looks is the phenotype. It is the summary of all the features you can see on the outside of your plant. It can also be smell and taste.]
Genotype – The genetic constitution of an individual, esp. as distinguished from the phenotype; the whole of the genes in an individual or group. [How your plant looks like inside, which features it can possibly inherit – you can’t see those – is called the genotype. It is the summary of all genetic information which your plant carries and can inherit to its offspring.]
Dominant – Of a gene or allele: expressed even when inherited from only one parent. Of a hereditary trait: controlled by such a gene; appearing in an individual to the exclusion of its allelic counterpart, when alleles for both are present. [A gene is said to be dominant when its effect can be seen in the phenotype of your plant. Only one dominant allele in the gene pair must be present to be seen in the phenotype of your plant].
Recessive – Of a gene, allele, or hereditary trait: Of a gene, allele, or hereditary trait: Of a gene, allele, or hereditary trait: Of a gene, allele, or hereditary trait: [A gene is called recessive when its effect can [A gene is called recessive when its effect can [A gene is called recessive when its effect can [A gene is called recessive when its effect can if you can see its expression in the phenotype if you can see its expression in the phenotype
Locus – A position on a chromosome at which a particular gene is located.
Chromosome – A threadlike structure of nucleic acids and protein which carries a set of linked genes and occurs singly in prokaryotes and in characteristic numbers, usu. paired, in the cell nuclei of higher organisms.