a) Novel Phenotype (9:3:3:1):

• A novel phenotype is a phenotype that is concerned with the unique visual appearance of an organism as compared with its parents.
• Eg: comb shape in poultry
• New phenotype results from interaction between dominants and also from both homozygous recessives.

b) Epistasis:

• Epistasis is a circumstance where the expression of one gene is affected by the expression of one or more independently inherited genes.
• For example, if the expression of gene #2 depends on the expression of gene #1, but gene #1 becomes inactive, then the expression of gene #2 will not occur.

• These are following types:

i) Complementary action (9:7):

• Two genes may be required to produce the same effect.
• Eg: Flower color in sweet pea.

ii) Inhibiting action (13:3):

• One gene may act as an inhibitor of the effect of another gene.
• Eg: aleurone color in maize.

iii) Duplicating action (15:1):

• Either of 2 gene may produce a similar effect or the same effect is produced by both of them together.
• Eg: Seed capsules of Bursa.

iv) Modifying action ( 9:3:4):

• One gene has no visible effect unless a second gene is present at another locus.
• Eg: Grain color in maize.

v) Additive or polymeric action (9:6:1):

• Two gene may produce the same effect, but the effects are additive if both genes are present.
• Eg: awn in barley.

vi) Masking action (12:3:1):

• One gene may hide the effect of a second gene when both are present.
• Eg: Seed coat color in barley.