Mendel and Definitions

Genetics: The study of various aspects of genes like their structure, location, function is called genetics.

Gene: The small portion of chromosome which is responsible to transfer the parental characters from one generation to another is called gene.

Heredity characters: Those characters which are able to transfer from generation to generation are called heredity characters. They are also called parental characters.

Father of genetics: Gregor john Mendel. He did his experiments on pea plant (Pisum sativum). Mendel chose pea plant because:

1. Pea plants are naturally self-pollinated and artificially cross-pollinated. It helps to maintain purity of character in off springs.
2. It has numbers of different numbers of distinguishable contrasting characters like tall and dwarf, red and white flowers. Therefore, the characters were easily distinguishable.
3. The hybrid plants, resulting from cross pollination, are also fertile. In many cases it is found that cross pollination gives infertile offspring.
4. A large number of progeny (off springs) can be obtained from a single plant.
5. The life cycle is of short duration. So results can be seen in short period.
6. Pea plants are very easy to handle no special care is required.

Seven characters studied by Mendel

Some Definitions:

1. Unit characters: Those characters of organism which can be taken as the base of the expression and are expressed externally i.e. can be seen with naked eye are called unit characters.
2. Types of experiments:
3. Monohybrid cross: If a single unit character is studied during an experiment then it is called monohybrid cross. E.g. Study of height in pea plant
4. Dihybrid cross: If two unit characters are studied during an experiment then it is called dihybrid cross. E.g. Study of height and pod shape in single experiment
5. Polyhybrid cross: If more than two unit characters are being studied in an experiment then it is called poly hybrid cross. E.g. Study of height pod color and shape of seed in the single experiment
6. Dominant characters: Those characters which are often expressed during a cross are called dominant characters. E.g. Tallness in height
7. Recessive characters: Those characters which are less prominent and are present in gene in hidden form are and less expressed are called recessive characters. E.g. dwarfness in height
8. Phenotypic character: Those characters which are expressed externally in the living organism so that are seen with naked eyes are called phenotypic characters.
9. Genotypic characters: those characters that are expressed through gene but can be seen or not seen with the naked eye are called genotypic characters.
10. Homozygous pair: A pair of gene which are responsible to () the same contrasting character is called homozygous pair. The pair of gene represented by TT is responsible for tallness in pea.
11. Heterozygous pair: A pair of gene, which is responsible for combining different contrasting characters, is called heterozygous pair. The pair represented by Tt; T represents the tallness and t represents dwarfness and the plant is hybrid (may be tall but not as tall as TT)

Hybrid: Those organisms which have heterozygous pair of genes are called hybrids.