(a) (i) What is the difference between the genotype and phenotype of an individual? [2 marks]
(ii) State two factors each which determine each of the terms in 4(a). [4 marks]

(b)       In a breeding experiment, a homozygous black dog (BB) was crossed with a homozygous white dog(bb) to produce black puppies in the first filial generation (F I)' The second filial generation produced a total of two hundred and forty (240) black and white puppies. With the aid of a genetic diagram, determine:
             (i)        the number of white puppies;
             (ii)       The number of black puppies in the second filial generation. [14 marks]

 

observation

The performance of candidates who attempted this question was impressive most candidates could
correctly differentiate between phenotype and genotype and state factors affecting both. In the
question on the breeding experiment, some candidates got the crossing in the genetic diagram
wrong but still arrived at the right answers and so lost many points.
The expected answers include:
Breeding Experiment

                              2nd filial general                       BB Bb        Bb bb
Phenotypic ratio 3 black: 1 white puppies
Calculation:
The number of white puppies using the phenotypic ratio 3 black: 1 white = 240
Total No. of puppies produced = 240
.'. No. of white puppies produced 14 x 240 = 60 white puppies
Number of black puppies = % x 240 = 180 black puppies.