Heredity and its Variation

If we see the offspring of any organism, it looks like its parent only, like a pup produced from bitch, kitten produced from a cat and bunny from a rabbit, similarly all plants also produce their own kind.

Asexually reproducing organisms look very much similar to their parents like all plants in a sugarcane field look very much similar to each other. 

In asexually reproducing organisms, variations are very little (brought only because of small changes created in DNA at the time of their replication).

Sexually reproducing organisms show great variation as compared to asexually reproducing organisms, because of involvement of two parents. So, their characters are varying between two parents. 

“Heredity is the passing of characters from parents to offsprings or one generation to next”. Genetics is a branch of biology which deals with the study of heredity and variations. 

The differences in the traits or characters among the individuals of a species are called variations. e.g. Plant height - tall and dwarf.

Sexually reproducing organisms show greater variations which may lead to increased survival of individual. So, greater diversity will be generated by sexual reproduction.

1.0Accumulation of Variations During Reproduction

Small variations are produced in each generation. These small variations accumulate generation after generation. These variations may enable or disable the organisms to cope with changes in the environment. Advantageous variations are selected by environmental factor. 

e.g., Bacteria that tolerate low temperature can survive in a cold wave. Such heritable variations lead to the evolution and formation of new species.

The offsprings are slightly different from each other. Some differences are unique and other are inherited from their respective parents.

2.0Terminology used

Alternative forms of a gene which are located on same position (loci) on the homologous chromosome are called alleles.

Chromosome is a thread like structure in the nucleus of a cell. It is formed of DNA which carries the genes.

Unit of heredity which transfers characters from parents to their offsprings during reproduction is called genes.

The genetic constitution of an organism or the description of genes present in an organism e.g., TT, Tt, tt is called genotype.

External and morphological appearance of an organism for a particular character is called phenotype. e.g., Tall, Dwarf.

Any character that appears in the F₁ generation offspring from a cross between parents possessing contrasting characters (such as tallness and dwarfness in pea plants) is called dominant character.

Recessive factor or allele is the one which is unable to express its effect in the presence of its contrasting factor in heterozygous state. Its effect can be seen in pure or homozygous state only.

In homozygous condition, two factors of a character are same (TT). In hybrid /heterozygous condition, two factors of a character are different (Tt). 

3.0Also Read