DNA BIO 101

For Questions 1 and 2, circle, highlight or bold the alternative a, b, c, or d that best answers the question.

 

1. 20% of all bases in a strand of DNA are guanine. From this you would expect the percentage of adenine to be:

 

(a) 10%

 

(b) 20%

 

(c) 30%

 

(d) 40%.

 

2. Part of a strand of DNA has the following sequence of bases. The base sequence of the complementary DNA strand would be:

 

A A T C C G G T A

 

(a) AAT CCG GTA

 

(b) CCG AAT TGC

 

(c) TTA GGC CAT

 

(d) TTA CCG GAT.

 

3. Meiosis is the name of the nuclear division that occurs during the production of gametes.

 

(a) Draw a series of six diagrams to illustrate the stages involved in meiotic division occurring in a cell containing two pairs of homologous chromosomes. Colour code the chromosomes using blue for the paternal chromosome and red for the maternal chromosomes.

 

 

 

Stage 1—diploid cell

 

 

 

 

 

 

Stage 2

 

 

 

 

 

 

 

Stage 3

 

 

 

 

Stage 4

 

 

 

Stage 5

 

 

 

 

 

Stage 5—gametes

 

 

(b) The gametes you have drawn at step 6 are not the only possible gametes that can be formed. Name the two processes that could result in different gametes being produced in stage 6 and draw a diagram to illustrate the gametes that would result.

 

Process of meiosis producing these gametes -Spermatogenenis

Process of meiosis producing these gametes –Oogenesis

 

4. What led Boveri and Sutton to independently make the link between chromosomes and the inheritance of genes?

They noticed a similarity between the behavior of chromosomes during cell division (meiosis) and the behavior of factors (genes) described by Mendel experiments. They carried out staining techniques which the chromosomes to be visible. Boveri used sea urchins to investigate inheritance patterns; while Sutton used grass hoppers to investigate meiosis.

 

5. The phenotype of an organism is determined by both the environment and genotype.

Outline two specific examples that you have studied that illustrate the effect of the environment on phenotype.

Development of diabetes type 2. The defect gene responsible for conversion of glucose to glycogen is inherited. The gene will express itself if factors in the environment become favorable such as lack of exercise and too many sugars.

The shoe size of an individual; if an individual never puts on shoes, the size is likely to be larger than an equal shoe size individual who puts on shoes continuously.

 

6. Below is a diagram depicting a short length of DNA.

 

 

(a) What three major components of DNA do the symbols A, B and C represent?

 

A.  Phosphate

B. Sugar

C. Bases

 

 

(b) Describe one modification that could be made to the diagram to make it a more accurate depiction.

 

In multi-compartmental methylationa of DNA, the methylation states of DNA are varied so as to significantly alter gene expression levels significantly

 

7. What part does each of the following play in protein synthesis?

(a) DNA

It ensures precise replication during protein synthesis

(b) Messenger RNA

It contains the information, the coding sequence, needed during the protein synthesis. They are transcripts. Also contains start and stop signals for translation.

 

(c) transfer RNA

The transfer RNA carry amino acids to the ribosomes during protein synthesis

 

(d) Ribosome

Ribosomes act as the sites for protein synthesis.

 

8. Mutations are a source of new alleles in organisms.

(a) Define a mutation.

 

Mutation is an irreversible, heritable change in the DNA sequence of a particular gene or chromosome.

 

(b) Outline evidence for the mutagenic nature of radiation.

 

  1. Hodgkin’s disease_
  2. Skin cancers in Australia where people are constantly exposed to UV rays from the sun
  3. Leukemia
  4. Deaths resulting from cancer after Hiroshima bomb.

 

(c) Given the original DNA and the mutated DNA form:

 

Original DNA

 

TCA CAG GCG AGT TCT CAT

 

Mutated DNA

 

TCA CAG CGCG AGT TCT CAT

 

Discuss the change that this type of mutation would have on the protein produced by the gene containing this base sequence.

 

This is insertion in gene mutation in which a nucleotide base is added to the gene sequence. The corresponding protein would amino acid residues. The function of the protein made from the sequence may or may not change.

 

9. Describe the concept of punctuated equilibria highlighting how it differs from the process proposed by Darwin.

Punctuated equilibrium is a theory on evolution of species that was first advanced by Niles Eldredge and Stephen Jay Gould who were American scientists. The theory proposes that most species have a relatively sudden origin which takes thousands and thousands of years and not millions and millions as traditional theories claim. The evolution of this species in the rest of their time on Earth is not significantly enough. This theory differs from Darwin’s theory of origin of species which proposes that gradual evolution of species is inevitable.

_____ http://science.jrank.org/pages/5591/Punctuated-Equilibrium.html __

 

10. Rosalind Franklin was not awarded the Nobel Prize along with Watson, Crick and Wilkins for discovering the structure of DNA. Do you think this was fair? Justify your answer with reference to their work and the importance of collaboration and communication in scientific research.

Her work on DNA remained largely unrecognized for along time until her colleagues, Watson, Crick and Wilkins, became recognized. However, some of her contributions were key to the study of DNA, for example, the famous “photograph 51” that illustrated the helical structure of DNA which she handed over in 1953 to Watson and Crick. It is therefore unfair not to have been nominated for the prize.  Probably she would have been next for the award had she not died of cancer soon after the awards of the colleagues. The rules of the Nobel Prize require that only the recipients of the prize must be alive.

11. Transgenic species are being produced more frequently and have caused a considerable amount of controversy.

 

(a) How are transgenic species produced?

Transgenic animals are produced by introduction of a foreign gene or genes (transgenes) into an animal whereby the transmission must be done through the germ line to ensure that all the cells in the animal, with the germ cells included, contain a duplicate of the genetic material.

 

(b) Give one example of transgenic species production to illustrate its use in:

Agriculture

Production of a new variety of cotton has been developed that uses a gene extracted from a bacterium known as Bacillus thuringiensis in the process of synthesizing a protein that is specifically toxic to insect pests such as bullworm

The control or treatment of disease

Transgenic cows that produce milk containing a natural protein that kills the bacteria responsible for animal mastitis. An example of such is illustrated below.

 

 

(c) Discuss one ethical concern that could be raised concerning the use of transgenic species.

 

One area of development involving use of transgenic species in GMO crops which are able to produce resistance and pesticides. The negative effects of this technology will lead to some weeds developing resistance to these herbicides and this is encouraged by cross pollination. Thus the potential benefit of the herbicide is negated.

 

12. For a named species, evaluate the potential impact of the use of reproduction technologies on its diversity.

Crops plants have been engineered which produce seeds that lose sterility before they actually become mature. Germination and growth of these plants is dependent on application of the same chemicals that cause the sterility.