Biology 3 Nov/Dec 2010

Biology Paper 3,Nov/Dec 2010

Questions:		1	2	3	4	Main

General Comments
Weakness/Remedies
Strength

Question 2
The diagrams labelled I, II and III below are illustration of fingerprints of three individuals. Study the diagrams and use them to answer questions 2(a) to 2 (b). Diagrams: I III (a) (i) Which type of variation is represented by the diagrams? …………………………………………........................................................................................... ................................................................................................................................ [2 mark ] (ii) Classify diagrams I, II and III I ...................................................................................................... II ...................................................................................................... III .....................................................................................................[3 mark ] (iii) Give the reasons for your classifications in 2(a)(ii) above ............................................................................................................[ 1 mark ] (b) State and explain the application of this variation …………………………………………………………………………………........................................ …………………………………………………………………………………………………………………………………. .............................................................................................................. ................................................................................................................. [5 marks] (c) The genetic diagram below is that of a tall cowpea plant which was crossed with a dwarf cowpea plant. Study the diagram and use it to answer questions 2( c) to 2( d) TT X tt -IV -V -VI Key - T - Tallness t - Shortness (i) What do the labels IV, V and VI represent in the diagram? IV. ................................................………………………………………………………………………………. V. ………………………………………………………………………………………………………………………………………… VI. ……………………………………………………………………………………………………………………………………….. [ 3 marks] (ii) What is the genotype of the individuals in VI? ………………………………………………………………………………………………………………………………………..[ 1 mark] (iii) Which of the Mendelian laws of inheritance does the diagram represent? …………………………………………………………………………………………………………………………………………. [4 marks] (d) (i) Using a genetic diagram illustrate a self cross between two of the individuals labelled VI (ii) Assuming that 400 offspring arise from the cross in 2( d)(i) above, deduce how many of them will be tall? ..................................................................................................................................... .................................................................................................................................... .................................................................................................................................. [ 3 mark ]
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OBSERVATION
This was the more popular question in this section and the performance of candidates on this question was fair. Most candidates could properly state the types of variation namely morphological and discontinuous but many candidates lost marks due to poor spelling. Most candidates were able to classify the finger prints and correctly state the application but could not state the basis of the classification. Expected answers include: Reasons for classification - It is due to differences in the arrangement/contour of the ridges on the human finger tips forming different patterns. Only few candidates could correctly label IV, V and VI and correctly state the offspring of a self cross of VI. Most candidates could however correctly state the Mendelian Law represented by the diagram. Most candidates were unable to calculate the number of tall plants in the offspring of the self cross. Expected answers include: Parts represented in diagram IV - Parents V - Gametes VI - F/F₁ generation Genotype in VI Tt Self cross of VI individuals Tt X Tt Parent Gametes Genotype Phenotype Detennination of number of tall plants Proportion of tall offspring = ¾ .', Proportion of tall = ¾ x 400 = 300 tall