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:
- Pea plants are naturally self-pollinated and artificially cross-pollinated. It helps to maintain purity of character in off springs.
- It has numbers of different numbers of distinguishable contrasting characters like tall and dwarf, red and white flowers. Therefore, the characters were easily distinguishable.
- The hybrid plants, resulting from cross pollination, are also fertile. In many cases it is found that cross pollination gives infertile offspring.
- A large number of progeny (off springs) can be obtained from a single plant.
- The life cycle is of short duration. So results can be seen in short period.
- Pea plants are very easy to handle no special care is required.
Seven characters studied by Mendel
|Character ||Dominant character ||Recessive character |
|Height of plant ||Tall (T) ||Dwarf (t) |
|Shape of the seed ||Round (R) ||Wrinkled (r) |
|Color of the seed ||Yellow (Y) ||Green (y) |
|Color of the seed coat ||Brown (B) ||White (b) |
|Shape of pod ||Inflated (I) ||Constricted (i) |
|Color of pod ||Green (G) ||Yellow (g) |
|Position of flower ||Axial (A) ||Terminal (T) |
- 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.
- Types of experiments:
- 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
- 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
- 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
- Dominant characters: Those characters which are often expressed during a cross are called dominant characters. E.g. Tallness in height
- 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
- Phenotypic character: Those characters which are expressed externally in the living organism so that are seen with naked eyes are called phenotypic characters.
- Genotypic characters: those characters that are expressed through gene but can be seen or not seen with the naked eye are called genotypic characters.
- 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.
- 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.
Things to remember
- The study of various aspects of genes like their structure, location, function is called genetics.
- The father of genetics is Gregor John Mendel.
- 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.
- Those characters which are often expressed during a cross are called dominant characters. E.g. Tallness in height.
- 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.
- Those organisms which have heterozygous pair of genes are called hybrids.
- It includes every relationship which established among the people.
- There can be more than one community in a society. Community smaller than society.
- It is a network of social relationships which cannot see or touched.
- common interests and common objectives are not necessary for society.
Videos for Mendel and Definitions
Introduction to Heredity
Mendel Genetics & Heredity Animation
Questions and Answers
Mendel selected pea plant for his experiment for the following reasons:
- The pea plant possesses a number of pair of contrasting characters such as red-white flower, round- wrinkle seed, tall-short plant etc.
- Pea plant can produce many generation in a short time i.e. short life cycle.
Yes, Mendel's law applies to human beings too. But while applying the law to the human beings, many problems would rise.
If he had carried his experiment on human beings instead of pea plants, he would have faced the following problems:
- There is absence of large number of contrasting pair characters in human beings.
- It is difficult to control the sexual reproduction.
Two probable causes that Mendel did not do is experiment in frog instead of pea plant are as follows:
- Safe reproduction cannot be done in frog.
- External fertilization occurs in frog and its life cycle is also long.
The characters which are transferred from parents to the offsprings are called hereditary characters. Genes transfer various characters from parents to offsprings.
The branch of biology concerned with the study of the mechanism of heredity and variation is called Genetics. Gregor Mendel is known as father of genetics.