<h2><strong>GENETICS</strong></h2>
<h2><strong>PAST KCSE QUESTIONS ON TOPICS</strong></h2>
<ol>
<li>The figure below is a structural diagram of a portion from a nucleic acid strand.</li>
</ol>
<p> ;</p>
<p><strong> &#8212; S &#8212; P &#8212; S &#8212; P &#8212; S &#8212; P &#8212; S </strong></p>
<p><strong> C G U C</strong></p>
<p>(a) Giving a reason, name the nucleic acid to which the portion belongs. ( 2 marks)</p>
<p>Name _________________________</p>
<p>Reason _________________________</p>
<p>(b) Write down the sequence of bases of a complimentary strand to that shown above ( 1 mark)</p>
<ol start="2">
<li>State two structural differences between ribonucleic acid ( RNA) and</li>
</ol>
<p>deoxyribonucleic acid ( DNA) ( 2 marks)</p>
<ol start="3">
<li>Name a disorder of human blood that is caused by mutation ( 1 mark)</li>
<li>State the function of deoxyribonucleic acid (DNA) molecule ( 1 mark)</li>
<li>Give a reason why it is only mutation in genes of gametes that influence evolution ( 2 marks)</li>
<li>In an experiment, red flower were crossed with plants with white flower. All the plants in the F1 generation had pink flowers.</li>
</ol>
<p>(a) Give a reason for the appearance of pink flower in the F1</p>
<p>generation ( 1 mark)</p>
<p>(b) If the plants from F1 generation were selfed, state the phenotype ratio of the F2 generation ( 2 marks)</p>
<ol start="7">
<li>State two characteristics that researchers select in breading programmes.</li>
</ol>
<p>( 2 marks)</p>
<ol start="8">
<li>Give an example of sex- linked trait in humans on; ( 2 marks)</li>
</ol>
<p>Y chromosome __________________</p>
<p>X chromosome __________________</p>
<ol start="9">
<li>In an experiment, a variety of garden peas having a smooth seed oat was crossed with a variety with a wrinkled seed coat. All the seeds obtained in the F1 had a smooth seed coat. The F1 generation was selfed. The total number of F2 generation was 7324.</li>
</ol>
<p>(a) Using appropriate letter symbols, work out the genotype of the F1 generation. ( 4 marks)</p>
<p>(b) From the information above, work out the following for the F2 generation</p>
<p>(i) Genotype ratio ( 2 marks)</p>
<p>(ii) Phenotype ratio ( 1 mark)</p>
<p>(iii) Wrinkled number ( 1 mark)</p>
<ol start="10">
<li>In a certain plant species, some individual plant may have white, red or pink flower. In an experiment a plant with white parent plant were pure lines. All the plants from F1 generation were pink. Using letter R to represent the gene for red colour and letter W for white colour;</li>
</ol>
<p>(a) Work out the genotype of F1 generation ( 3 marks)</p>
<p>(b) If the plants from F1 generation were selfed, what would be the phenotypic ratio of the F2 generation? ( 3 marks)</p>
<p>(c) What is the genetic explanation for the absence of plants with red and white in the flower F1 generation? ( 2 marks)</p>
<ol start="11">
<li>In a breeding experiment, plants with red flower were crossed. They produced 123 plants with red flowers and 41 with white flowers.</li>
</ol>
<ul>
<li>Identify the recessive character. Give a reason</li>
<li>What were the genotypes of the parent plants that give rise to the plants with red and white flowers?</li>
<li>If the white flowers were selfed, what would be the genotypes of their offspring?</li>
</ul>
<ol start="12">
<li>(a) Name two disorders in humans caused by gene mutation</li>
</ol>
<p>( 2 marks)</p>
<p>(b) Describe the following chromosomal mutations</p>
<p>(i) Inversion ( 2 marks)</p>
<p>(ii) Translocation</p>
<p>(c) In mice the allele for black fur is dominant to the allele for brown fur. What percentage 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)</p>
<ol start="13">
<li>(a) What is meant by the term allele? ( 1 mark)</li>
</ol>
<p>(b) Explain how the following occur during gene mutation</p>
<p>(i) Deletion ( 1 mark)</p>
<p>(ii) Inversion ( 1 mark)</p>
<p>(c) What is a test- cross? ( 1 mark)</p>
<ol start="14">
<li>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.</li>
</ol>
<ul>
<li>(i) Using letter G to represent the gene for purple colour, work out</li>
</ul>
<p>the genotypic ratio of the offspring ( 5 marks)</p>
<p>(ii) State the phenotype of the offspring ( 1 mark)</p>
<p>(b) What is genetic engineering? ( 1 mark)</p>
<p> ;</p>
<ol start="15">
<li>Define the following terms as used in genetics.</li>
</ol>
<p>(i) Alleles</p>
<p>(ii) Genotype</p>
<p>(iii) Phenotype</p>
<ol start="16">
<li>A farmer mated his dark red cow with a white bull. The cow gave birth to a light red calf</li>
</ol>
<ul>
<li>State why the calf is light red and not dark red or white</li>
<li>If a light red bull is mated with a dark red cow, work out using appropriate letter symbols the probability of getting a light offspring</li>
</ul>
<ol start="17">
<li>(a) What is meant by linked genes?</li>
</ol>
<p>(b) (i) In fruit flies (Drosophila) the gene for red eyes ® is dominant over</p>
<p>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.</p>
<p>(ii) Work out the ratio of the expected phenotypes if a red- eyed female offspring from the cross- described in (i) above is mated with red- eyed males.</p>
<ol start="18">
<li>(a) Explain the term variation with reference to the study of genetics.</li>
</ol>
<p>(b) Using relevant examples distinguish between discontinuous variation and continuous variation</p>
<p>(c) What is the importance of genetic variation?</p>
<p>(d) Describe one example where genetic variations has helped a species to survive</p>
<ol start="19">
<li>The diagram below shows the base sequence of part of a nucleic acid stand. Observe it and answer the questions that follow</li>
</ol>
<p>G T T A G C T G A</p>
<p>(a) What do the letters G, T , C and A represent?</p>
<p>(b) Giving your reasons state whether it is part of DNA or an RNA strand.</p>
<ul>
<li>Show the complementary DNA strand</li>
<li>Show the complimentary RNA strand</li>
</ul>
<ol start="20">
<li>In human couples the sex of a baby is determined by the man. Explain this statement.</li>
</ol>

