NUS GEK1527 Genes and Society Mid Term Assignment

Genes and Society (GEK1527/LSM1302)Assignment
Academic Year 2008/2009 Semester 1

1a) Gene A is 4000 bp while gene B is 3000 bp. Therefore the protein encoded by
gene A must be larger than the protein encoded by gene B. [1 mark]

False. During post-transcriptional modification in eukaryotic systems where the precursor messenger RNA is converted into mature messenger RNA, splicing occurs. Introns which are the non-coding sections in the precursor mRNA are removed by splicing and the resulting protein coding exon length is not totally dependent on the original gene length.

b) If we want to grow a bacterial clone with a plasmid that carries a desired DNA
fragment inserted within the antibiotic ampicillin resistance gene, we should
not grow it in a medium containing ampicillin. [1 mark]

True. The antibiotic resistance gene in the plasmid would have been disrupted by the desired DNA fragment. The bacterial clones that take up the desired plasmid will not be resistant to ampicillin and will not survive in a medium containing ampicillin.

c) Clones isolated from cDNA libraries contain promoter sequences. [1 mark]

False. Promoter sequences are found in DNA that allows transcription of a gene. cDNA is produced from fully transcribed mRNA and therefore contains only the coding regions and not the promoter regions.

2. DNA sequencing of your own two beta-globin alleles (one from each of your two chromosomes 11) reveals a mutation in one of the alleles. Given this information alone, what other information would you like to have to assess your risk of being a carrier of an inherited disease that could be passed on to your children? [2 marks]

An important information to know would be the type of mutation that has occurred and the consequence, for example it would less likely cause disease if it is a Silent Mutation. Sequencing of the spouse’s DNA would also be useful in determining the risks of disease passing on to the children. Also, the family’s history of genetically related diseases will be useful as well. And if possible, knowing the dominance of the mutated allele will be important as well.

3. Describe the major differences between the central dogma (i.e. how genetic
information are stored, transmitted, processed, expressed and/or regulated) in
prokaryotic and eukaryotic cells. [3 marks]

In eukaryotic cells, DNA is stored in the nucleus while for prokaryotic cells their circular DNA is found in the nucleoid region.

For eukaryotic cells, transcription occurs in the nucleus while translation occurs outside of the nucleus in the cytoplasm. Prokaryotic cells do not have a nucleus membrane barrier and thus translation can transcription can happen at the same time.

In eukaryotes, the DNA has intervening sequences called introns within the gene that separate coding fragments called exons, making alternative splicing possible. Prokaryotic genes do not have introns and are continuous.

4. Why some traits such as intelligence and diligence are not inherited in a
Mendelian fashion? [2 marks]

Intelligence and diligence are examples of non-inherited traits there are affected more by the environment and parental upbringing than genetics. However, even though there is still possibility that genetics do play a part in the manifestation of these traits, they are quantitative characteristics and will be affected by more than one gene and thus are not inherited in a Mendelian fashion where each trait is affected by only one gene.