To calculate this, the Hardy-Weinberg principle can be used:
p² + 2pq + q² = 1 and p + q = 1
where p and q are the frequencies of the alleles (p - dominant, q - recessive), and p², q² and 2pq are the frequencies of the genotypes.
a) Since 32 plants have rough seed (recessive genotype: q²) out of 100 plants in total, then
q² = 32/100 = 0.32
b) q = √q² = √0.32 = 0.56
c) Since p + q = 1, then
p = 1 - q = 1 - 0.56 = 0.44
d) 19 plants with rough seeds (recessive genotype: q²) in a population of 100 means that q² = 19/100 = 0.19
We need to calculate p (the allele frequency for smooth seeds).
We can find q because we know q²:
q = √q² = √0.19 = 0.44
Since p + q = 1, then
p = 1 - q = 1 - 0.4 = 0.56
