Question

(a) (i) Compare the pattern of inheritance of flower colour in garden pea plant (violet/white) with snapdragon plant (red/white) on the basis of the following:
1. F1 phenotypic expression.
2. Expected phenotypic and genotypic expression of F2 generation.
3. Conclusion you reached at the end of the comparison.
(ii) List any two characteristics of pattern of inheritance of human blood group ABO.
OR
(b) (i) Draw a schematic, self-explanatory labelled diagram of lac operon in a ‘switched on’ condition.
(ii) Why is regulation of lac operon referred to as negative regulation?

Hint:

(a) (i) Inheritance patterns can vary between traits, with some showing complete dominance (pea plant) and others incomplete dominance (snapdragon).
(ii) The ABO blood group system is an example of codominance and multiple allelism, unique among genetic traits.
(b) (i) The lac operon is switched on in the presence of lactose, enabling the expression of genes involved in lactose metabolism.
(ii)

Answer 1

(a) (i) 1. F1 phenotypic expression:
- Garden pea: All F1 plants are violet (dominant trait).
- Snapdragon: All F1 plants are pink (incomplete dominance).
2. F2 generation:
- Garden pea:
-- Phenotypic ratio: 3:1 (violet: white)
-- Genotypic ratio: 1:2:1 (VV:Vv:vv)
- Snapdragon:
-- Phenotypic ratio: 1:2:1 (red: pink: white)
-- Genotypic ratio: 1:2:1 (RR:Rr:rr).
3. Conclusion:
- In garden pea, flower colour inheritance follows complete dominance.
- In snapdragon, flower colour inheritance follows incomplete dominance.
 

(ii) 1. The ABO blood group exhibits codominance, where both A and B alleles are expressed equally in the AB blood group.
2. The blood group also shows multiple allelism, as there are three alleles (IA, IB, i) for a single gene.
 

OR
(b) (i)
 

(ii) The lac operon is referred to as negative regulation because the operon is switched off by the binding of a repressor protein to the operator region in the absence of lactose. Lactose acts as an inducer by removing the repressor.