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.
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.
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.
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.
The chromosome number is one of the primary bases of hybridization in agricultural crops as well as in animals.
The diploid numbers of chromosomes are essentially constant within the same species.
It is an important topic of review in basic plant breeding.
It is the general rule that successful crosses are easier to achieve between individual plants under the same species rather than between different species under the same genus (interspecific cross).
Consequently, it is more difficult to produce an intergeneric hybrid. In sum, individuals which are closely related taxonomically are much easier to cross.
Gregor Mendel is now popularly called the Father of Genetics.
The title is just fitting for one who founded the basic principles of heredity and variation in living organisms.
He did not know it during his lifetime, but he was destined to become one of the most influential persons in the growth of biology.
In 1962, James Watson, Francis Crick, and Maurice Wilkins jointly won the highly coveted Nobel Prize for having discovered the structure of DNA, the “secret of life.”
Rosalind Franklin would also have shared the prize had she lived (Phelan 2006). (Click here to read a surprising update on Watson’s and Crick’s Nobel prize medals).
The Mendelian Principle or Law of Segregation, also called Mendel’s First Law, has been stated in the following manner: a hybrid between two parents differing in a set of characters possesses both parental factors which subsequently separate (segregate) in the gametes.
This genetic principle, along with complete dominance, modified the early belief that heredity is purely a “blending” process in which the offspring exhibits a character that is intermediate between the two parents.
Originating from Gregor Mendel’s historic research work with the garden pea, the law established that the transmission of traits from parents to progeny is carried by elementary units, which he called a factor, in a uniform, predictable fashion.
This “factor” is now called gene or, with reference to those in the same gene pair but carries the blueprint for contrasting characteristics, alleles.
This Law of Segregation is one of two laws Mendel formulated providing for the fundamental rules in the transmission of traits from parents to progeny.
