Question

It had always been assumedthat eukaryotic genes were similar in organization to prokaryotic genes. However, modern techniques of molecular analysis indicated that there areadditional DNA sequences that lie within the coding region of genes, Exons are the DNA sequences that code for proteins while introns are the intervening sequences that have to be removed. The graph shows the number of exons found in genes for three different groups of eukaryotes. 5. Percentage of genes 100 80 Saccharomyees cevevisiae (a yeast) 60 40 20 40 30 Drosophila melanogaster (fruit fly) 20 10 20 i5 Mammals 10 1 234567N9 10 1 12 13 14 15 16 17 18 19 20 3040 460>60 Number of exons Calculate the percentage of genes that have five orless exons in mammals. (1mark) b) a) Describe the distribution ofthe number of exons andthe percentage of genes in D. melanogaster. (2 marks). c) Compare the distributions ofthenumber of exons foundin genes of S. cerevisiae and mammals. (1mark) Suggest onereason for the differences in the numbers of exons found in genes of d) S. cerevisiae andmammals. (1mark)

Answer 1

B. Drosophila has higher percentage for those genes which have only 2 exons .Percentage of genes is between 0 to 5 which has more than 60 exons .

C. Both yeast and mammals show similarity when less no of exons are plotted against percentage of genes .It means because of small genome size yeast rarely show large no of exons in genes .

D. Yeast is an single celled eukaryotic fungi which has small sized genome as compared to mammals . This affects no of Exons per gene.