Answer:
1. (i) Purple flowers: xy
(ii) Red flowers: x(1-y)
(iii) White flowers: (1-x)(1-y)
2. x = 0.4816 and y = 0.4806
3. The probability that it has two P alleles is y^2.
4. The probability that a seed of this type carries two P alleles is 0.5 x y^2.
Gregor Mendel famously carried out experiments on sweet peas. Three naturally
occurring varieties of sweet peas have purple, red and white flowers. The flower colour may be
assumed to be determined by two genes. The first gene has two alleles: R and r. A sweet pea
with one or more R alleles will have red flowers. The second gene also has two alleles: P and
p. A sweet pea with no R alleles but with one or more P alleles will have purple flowers. If the
sweet pea’s alleles are rr and pp, the flowers will be white.
Let x denote the proportion of R alleles for the first gene amongst the all the sweet peas
cultivated in a particular garden centre, with 1 − x the proportion of r alleles; let y similarly
represent the proportion of P alleles, 1 − y the proportion of p alleles.
1. Calculate, in terms of x and y, the probability that a randomly selected sweet pea from
the garden centre has (i) purple flowers, (ii) red flowers, (iii) white flowers.
2. Given that 48.16% of the sweet peas in the garden centre have red flowers and 48.06% have purple
flowers, calculate the values of x and y.
3. A sweet pea with purple flowers is selected at random from the garden centre. What is
the probability that it has two P alleles?
4. The pollen from a sweet pea that has two P alleles always carries the P allele, whereas
the pollen from a sweet pea that has one P and one p allele has a 50/50 chance of carrying
either allele. A species of bee visits only purple-flowered sweet peas: seeds that develop
from pollination by such a bee carry one allele from the pollen and one from the plant
which was pollinated. What is the probability that a seed of this type carries two P alleles?
1 answer