In a breeding experiment, plants with red flower were crossed. They produced 123 plants with red flowers and 41 with white flowers.

(a) Identify the recessive character. Give a reason

(b) What were the genotypes of the parent plants that give rise to the plants with red and white flowers?

(c) If the white flowers were selfed, what would be the genotypes of their offspring?

12. (a) Name two disorders in humans caused by gene mutation

( 2 marks)

(b) Describe the following chromosomal mutations

(i) Inversion ( 2 marks)

(ii) Translocation

(c) In mice the allele for black fur is dominant to the allele for brown fur. Whatpercentage offspring would have brown fur from a cross between heterozygous black mice and brown mice? Show your working. Use letter B to represent the allele for black colour. ( 4 marks)

13. (a) What is meant by the term allele? ( 1 mark)

(b) Explain how the following occur during gene mutation

(i) Deletion ( 1 mark)

(ii) Inversion ( 1 mark)

(c) What is a test- cross? ( 1 mark)

14. In maize the gene for purple colour is dominant to the gene for white colour. A pure breeding maize plant with purple grains was crossed with a heterozygous plant.

(a) (i) Using letter G to represent the gene for purplecolour, work out

the genotypic ratio of the offspring ( 5 marks)

(ii) State the phenotype of the offspring ( 1 mark)

(b) What is genetic engineering? ( 1 mark)

15. Define the following terms as used in genetics.

(i) Alleles

(ii) Genotype

(iii) Phenotype

16. A farmer mated his dark red cow with a white bull. The cow gave birth to a light red calf

(a) State why the calfis light red and not dark red or white

(b) If a light red bull is mated with a dark red cow, work out using appropriate letter symbols theprobability of gettinga lightoffspring

17. (a) What is meant by linked genes?

(b) (i) In fruit flies (Drosophila) the gene for red eyes is dominantover

the one for white - eye (r). If a true breeding white - eyed male, all the offspring will be red eyed. However, if a true - breeding white- eyed female is mated with a true- breeding red- eyed male, all the female offspring will be red - eyed. Explain this apparent contradiction.

(ii) Work out the ratio of the expected phenotypes if a red- eyed female offspring from the cross- described in (i) aboveis mated with red- eyed males.

18. (a) Explain the termvariation with reference to the study of genetics.

(b) Using relevant examples distinguish between discontinuous variation andcontinuous variation

(c) What is the importance of genetic variation?

(d) Describe one example where genetic variations has helped a species to survive

19. The diagram below shows the base sequence of part of a nucleic acid stand. Observe it and answer the questions that follow

G T T A G C T G A

(a) What do the letters G, T , Cand A represent?

(b) Giving your reasons state whether it is part of DNA or an RNA strand.

(c) Show the complementary DNA strand

(d) Show the complimentary RNA strand

20. In human couples the sex of a baby is determined by the man. Explain this statement.