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.
- 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.
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