Concept of Gene

Gene is the basic unit of biological information. In fact DNA stores all sorts of biological information coded in the sequence of its bases in a linear order, and genes are actually parts of DNA comprising its base sequences.

Importance.

Hereditary characteristics pass from parents to offspring through genes in their gametes. Genes are responsible for producing startling inherited resemblances as well as distinctive variations among generations.

 When these pass in the form of intact parental combination between generations, inherited similarities are conserved; but

 When these shuffle, mutate or juggle with each other, variations emerge.

Gene Pair.

Genes form pairs on pairs of homologous chromosomes. One member of a gene pair is located on one homologue, and the other member on the other homologue. Locus. The position of a gene on the chromosome is called its locus.

Allele.

Partners of a gene pair are called alleles. Each allele of a gene pair occupies the same gene locus on its respective homologue. Both alleles on one locus may be identical, or different from each other. Phenotype Phenotype is the form of appearance of a trait. A flower may be red or white in colour. Flower colour is a trait and red and white are its two phenotypes. Genotype Genotype is genetic complement of trait.

Each form of expression is determined by a different allele of the colour gene in flower. Allele ―R‖ is the determiner for redness, while ―r‖ is the determiner for whiteness.

Homozygous Gene Pair.

If both alleles of a gene of same locus are identical then it is described as homozygous gene pair. i.e. RR or rr Heterozygous Gene pair. If both alleles of a gene of same locus are different then it is described as heterozygous gene pair. i.e.

Rr. Dominant Allele.

The alleles, which express their effects in phenotypes even in heterozygous condition. These are always described by capital letter. i.e. R or Y Recessive Allele. Those alleles whose effects remain hidden in phenotypes in heterozygous condition and only expressed in homozygous condition are said to be recessive allele. These are always described by small letters. i.e. r or y.

Jumping genes They do not settle peacefully on their loci, they keep on hopping on different loci on the same chromosome or other chromosomes.

Gene pool.

Population.

Any group of interbreeding organisms of the same species that exist together in both time and space is called a population.

Gene Pool.

All the genes/alleles found in a breeding population at a given time are collectively called the gene pool. It is the total genetic information encoded in the total genes in a breeding population existing at a given time.

BeanBag Genetics.

If we imagine population not as a group of individuals, but as a group of individually segregating and randomly assorting alleles, we can understand the concept of ―beanbag genetics‖.

The alleles are like beans in a beanbag. The entire beanbag full of beans is the gene pool of the population. In the beanbag approach we can imagine the entire gene pool comprising

 all the alleles for all the different traits at once, or

 We can just focus on some subset, such as all the alleles for a single trait. For convenience, we can focus on the gene pool for a single particular trait. A sample population of 100 diploid plants, some of which bear red flowers, others bearing white flowers has a sum total of 200 of all the different alleles (R or r) for flower colour trait as its gene pool.