For the MN-blood group system, the frequencies of M and N alleles are 0.7 and 0.3, respectively. The expected frequency of MN-blood group bearing organisms is likely to be

Hardy-Weinberg principle stated that in a given population the frequency of occurrence of alleles of a gene is supposed to remain fixed and even remain the same through generations. He represented it using algebraic equation (p+q)² = p² + 2pq + q² = 1, where p and q are individual frequencies of two different types of alleles.

So the expected frequency can be calculated using this equation.

For MN-blood group system:

Let frequencies of M be p, and from question p = 0.7

Let frequencies of N be q, and from question p = 0.3

Substituting these values in the above equation, we get

(p + q)² = p² + 2pq + q² = 1

(p + q)² = (0.7)² + 2(0.7)(0.3) + (0.3)² = 1

(p + q)² = 0.49+0.42+0.09 = 1

So from the above equation we can see that frequency of MN-blood group organism is 2pq = 0.42, or 42%.

So, the expected frequency of MN-blood group bearing organisms is likely to be 42%.

Hence the correct answer is option (a).