Agriculture

Gregor Mendel used the common garden pea in his experiments the results of which became the basis of the science of genetics.

It was not by accident that it became his experimental plant.

Even from the start, he was already aware that the right experimental plants must be used in order to avoid the “risk of questionable results”.

Consequently, he developed criteria in the selection of test plants for his study.

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Familiarity with crop classifications according to the methods of pollination is important in plant breeding.

This is so because of their effect on the applicability of certain breeding methods and techniques.

For example, pureline selection applies to highly self-pollinating crops.

In crop plants with high percentages of natural cross-pollination, controlled selfing is necessary to avoid contamination by foreign pollen.

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It is now known that there are various types of dominance.

The most popular in Mendelian genetics is complete dominance, but others also exist.

Each of these determines the phenotypic manifestation of a single gene pair in the absence of epistasis or interallelic gene interaction. 

These dominance relations involve intraallelic rather than “interallelic” gene interaction.

The Latin prefix “intra” means within or inside; “inter” means between or among (Borror 1988).

Intraallelic interaction refers to the interaction of alternative alleles within the same gene pair (located in the same locus in the chromosome) as if other gene pairs are absent.

As to the genotype TtGg, this means that the interaction involves that of T with t and of G with g, but not between either T or t with either G or g, or between separate allelic combinations.

Intraallelic interaction, therefore, occurs in the monohybrid which has a single gene pair, or is presumed in a multi-hybrid in which gene pairs are treated separately with the assumption that interlock gene to gene interaction does not exist even if it does.

This is consistent with Mendel’s Law of Independent Assortment which provides that each gene pair acts independently of other gene pairs. 

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Familiarization with the common terms in genetics is important in understanding the Mendelian laws or principles, and the role of genetic factors in plant growth and development.

Mendel’s parental “factor” is now referred to by the common term gene.

Gene is probably the most commonly used term in genetics and so deserves more elaboration.

The genes consist of deoxyribonucleic acid or DNA, so-called the chemical basis of heredity.

They are carried in the chromosomes, the physical basis of heredity, within the cell.

The chromosomes are those that appear under magnification as coiled, contracted, threadlike bodies in the nucleus at a certain stage of cell division in diploid somatic cells.

In diploid organisms like humans the chromosomes, and the genes, normally occur in two forms: haploid or singly (1N) in the sexual cells or gametes, and diploid or in pair (2N) in the somatic cells.

Somatic cells refer to the body cells, meaning all cells to the exclusion of the sexual cells or gametes.

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