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Genetics

Q1. Genetics Q and A

1a)   what is a test cross?                              (1 mark)

b)   The figure below is a structural diagram of a portion from a nucleic acid strand.

Giving a reason, name the nucleic acid to which the portion belongs.                  (2 marks)      

c) Write down the sequence of bases of the complementary strand to that shown above.       (1 mark)

2. The diagram below shows a template strand of the Deoxyribonucleic acid molecule. 

i) Complete the diagram by drawing the missing complimentary strand.                                  (1 mark)

ii) Name two chemical components that make the backbone of deoxyribonucleic acid molecule. (2marks)

(a)A woman who is a carrier for haemophilia got married to normal man. Work out the genotypes of the offsprings. Take the gene for haemophilia to be “h”                                           (4 marks)

(b)Name one disorder in humans due to chromosomal mutations.                                         (1marks)

3. Explain why the garden pea plant was preferred by Gregor Mendel in his crossing experiments (3mks)

4. Give two structural differences between DNA and RNA molecules.                                                (2mks)

5. In a certain plant species which is normally green, a recessive gene for colour (n) causes the plant to be white when present in homozygous state such plants die at an early stage; The plants are pale green in colour when in heterozygous state and grow to maturity.

(a)Give a reason for the early death of plants with homozygous recessive gene.                      (1mk)

(b)If a normal green plant was crossed with the pale green plant, what would be the genotypes of the F1 generation (use punnet square to work out the answer)                                                 

(c)If seeds from the heterozygous plants were planted and the resulting seeds planted, work out the phenotypic ratio of plants that would grow to maturity.                                                      (3mks)

(d)Explain the occurrence of the pale green colour in the heterozygous plants.                         (1mk)

6. Mr. Juma has sued Serenity Hospital on grounds that their child was wrongly identified such that they got the wrong one. The child is blood group O. Mr. Juma is blood group AB while Mrs. Juma is heterozygous blood group A.

(a)Work out the possible blood group of their offsprings.                    (4 marks)

(b)Is Mr. Juma justified in his claims?                                                  (1 mark)

7. The diagrams below illustrate some chromosome mutations.

 (a)Identify the mutations illustrated above.                              (3 marks)

 (b) Give an example of a disorder in humans caused by mutation A above.               (1 mark)

(c) Name a disorder of blood caused by gene mutation.           (1 mark)

(d)Name two mutagens.                                                            (2 marks)

(e)Give an example of a beneficial mutation in plants.                                     (1 mark)

8. a) Name two disorders in human caused by gene mutation              (2marks)        

b) Give two examples of continuous variation in plants                       (2marks)

9. In maize the gene for the purple colour is dorminant for the gene for white colour. A purple colour was crossed with heterozygous plant. Using letter G to represent the gene for purple colour, work out the     genotypic ratio of the offspring. Show your working.                                    (5marks)

10. The following are short messages (sms) on cell phone communication between Mrs. Mkenzie and her   husband. They can be used as analogies of gene mutation

(a)For each of these messages identify the type of gene mutation illustrated                   (4marks)

(b)State one example of chromosomal mutation that lead to 

(i)Change in chromosomal structure                (1mark)

(ii)Change in chromosomal number       (1mark) 

(c)Explain why genetic counselling is termed as one practical application of genetics     (2marks)

13. a)  what is sex linkage?                                                                               (1mark)

b)  Name the sex linked trait that are only in male                                                (2marks)

14. Pure breed of red cows and pure breed of white bulls were crossed to give F1 calves which had a mixture of red and white coat known as roan. The F1 were selfed.

(a)Using letter R to represent gene for red colour and W to represent gene for white colour work out the phenotypic ratio of  F2.                                          (4 marks)

(b)Work out the genotypic ratio of a cross between F1 offspring and white bull. (3marks)

(c)Comment on the gene(s) controlling the colour of coats in cattle mentioned above.           (1mark)

15. (a) What is mutation?                                                                                              (1mark)

(b) Name one disorder caused by gene mutation and one disorder caused by chromosome mutation. (2marks)

Gene mutation                                                   

Chromosome mutation               

16. a)  What is heterozygous advantage?           (1 Mark)

 b)  Give an example.              (1 Mark)

17. (a)  What is meant by the term              (2mks)

(i)Allele

(ii)Test cross

(b)Describe the following chromosomal mutations:

 i) Inversion            (1mks)

ii) Translocation            (1mks)

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

18. Explain the meaning of the following terms                                                                           

(i)Phenotype                (1 mark)

(ii)Test cross                (1 mark)

19. The diagram below represents a stage during cell division

ii) Give two reasons for your answer in a) i) above               (2mks)

b) Name the structure labeled M                                              (1 mark)

20. A cross between a red flowered plant and while flowered plant produces plants with pink flowers. Using letter R to represent the gene for red colour and W for white colour,

(a)What were the parental genotypes?                                       (1 mark)

(b)Work out a cross between F1 plants.                        (4 marks)

(c)i)  Give the phenotype ratio of F2 plants               (1 mark) 

ii) Genotypic ratio of F2 plants   (1 mark)

(d)Name the characteristic in humans which is controlled by multiple alleles                (1 mark)