(a) Chloroplast inheritance
(b) Mitrochondrial inheritance

The term genotype is the genetic constitution of an individual. The term phenotype refers to the observable characteristic of an organism.

(a) Classical genetics
(b) Molecular genetics
(c) Population genetic
(d) Quantitative genetics

A group of genes that together determine a characteristic of an organism.

"Genetics" is the branch of biological science which deals with the mechanism of transmission of characters from parents to off springs.

(i) Back cross is a cross of F, hybrid with any one of the parental genotypes. 
(ii) They are of two types - Dominant back cross recessive back cross.

Seven characters of pisum satiyum studied by Mendel.

Atavism is a modification of a biological structure whereby an ancestral trait reappears after having been lost through evolutionary changes in the previous generations. Evolutionary traits that have disappeared phenotypically do not necessarily disappear from an organism's DNA. The gene sequence often remains, but is inactive. Such an unused gene may remain in the genome for many generations. As long as the gene remains intact, a fault in the genetic control suppressing the gene can lead to the reappearance of that character again. Reemergence of sexual reproduction in the flowering plant Hieracium pilosella is the best example for Atavism in plants.

The Law of Segregation (Law of Purity of gametes): Alleles do not show any blending. During the formation of gametes, the factors or alleles of a pair separate and segregate from each other such that each gamete receives only one of the two factors. A homozygous parent produces similar gametes and a heterozygous parent produces two kinds of gametes each having one allele with equal proportion. Gametes are never hybrid.

Incomplete Dominance	Co-dominance
When one allele is not completely dominant to another allele.	lt occurs due to simultaneous expression of both alleles in the heterozygote.
E.g: Flowers colour of Mirabilis Jalapa	E.g:  ABO blood group system in human beings.

1. It is found in 40'ciock plant (Mirabilis jalapa).
2. Two types of variegated leaves.
(i) Dark green leaved plants
(ii) Pale green leaved plants
3. When the pollen of dark green leaved plant (male) is transferred to the stigma of pale green leaved plant (female) and pollen of pale green leaved plant is transferred to the stigma of dark green leaved plant, the F₁ generation of both the crosses must be identical as, per mendelian inheritance.
4. But in the reciprocal cross the F₁ plant differs from each other.
5. In each cross, the F₁ plant resembles female plant.
6. This inheritance is not due to nuclear gene.
7. This is due to the chloroplast gene found in the ovum of the female plant which contributes the cytoplasm.
8. During fertilization male gamete contribute only the nucleus but not cytoplasm.

Continuous variation Discontinuous variation Inheritance of phenotype is determined by the combined effects of many genes. The characteristics are controlled by one or two major genes which may have two or more allelic forms. Most of the characteristics exhibit a complete gradation, from one extreme to the other. Individuals produced by this variation show differences without any intermediate form between them. The variation may be due to the combining effects of environmental & genetic factors. They are unaffected by environmental conditions. This is also known as quantitative inheritance. This is also known as qualitative inheritance, E.g. Human height & skin colour E.g. Style length in Primula, plant height of garden pea.

Interlocus interactions take place between the alleles at different loci i.e. between alleles of different genes
Dominant Epistasis: It is a gene interaction in which 2 alleles of a gene at one locus interfere & suppress or mask the phenotypic expression or mask the phenotypic expression of a different pair of alleles of another gene at another locus.
The gene that suppresses or masks the phenotypic expression of a gene at another locus is known as epistatic. The gene whose expression is interfered by non-allelic genes & prevents from exhibiting its character is known as hypostatic.
When both the genes are present together, the phenotype is determined by the epistatic gene and not by the hypostatic gene.
In the summer squash, the fruit colour locus has a dominant allele 'W' for white colour & a recessive allele 'w' for coloured fruit.
'W' allele is donminant that masks the expression of any colour. In another locus hypostatic allele 'G' is for yellow fruit and its recessive allele 'g' for green fruit.
In the first locus the white is dominant to colour where as in the second locus yellow is dominant to green.
When the white fruit with genotype WWgg is crossed with yellow fruit with genotype wwGG, the F1 plants have white fruit and are heterozygous (WwGg).
When F1 heterozygous plants are crossed they give rise to F2 with the phenotypic ratio of 12 white:3 yellow: 1 green.

Since W is epistatic to the alleles 'G' and 'g'. the white which is dominant, masks the effect of yellow or green.
Homozygous recessive ww genotypes only can give the coloured fruits (4/16).
Double recessive 'wwgg' will give green fruit (1/16).
The Plants having only 'G' in its genotype (wwGg or wwGG) will give the yellow fruit(3/16).