(a) (i) What is the difference between the genotype and phenotype of an individual?
(ii) State two factors each which determine each of the terms in (a)(i).
(b) In a breeding experiment, a homozygous dog (BB) was crossed with a homozygous white dog (bb) to produce black puppies in the first filial generation (F1) 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.
Explanation
(a)(i) Difference between genotype and phenotype: A person’s genotype is the sum total of the person’s genetic constitution; while the phenotype is the observed trait/physical characteristics.
(ii) Factors which determine genotype: –
- Genotype of parents
- Mutation.
Factors which determine phenotype: –
- Genotype
- Environment;
- Diet
- Health.
(b)
Phenotypic ratio 3 black 1 white puppies
(b) Calculation: The number of white puppies using the phenotypic ratio
3 black: 1 white = 24
Total No of puppies produced = 240 .
No of white puppies produced = ¼ x 240 = 60 white puppies
(b)(ii) Number of black puppies = ¾ x 240 = 180 black puppies
OR calculation b(ii)
No of black puppies ¾ x 240 = 180
b(i) No of white puppies ¼ x 240 = 60