Question

1. What are stromatolites?

2. Who is the first scientist to construct a universal tree of life and how was this tree inferred?

3. Briefly explain/define horizontal gene transfer.

           

4. What is the endosymbiotic hypothesis?

5. What does PCR stand for and what is it used for?

Answer 1

1. Stramatolites are special rock like structures formed of lime secreting cyanobacteria and trapped sediment in shallow water.

2. Carl Woese. The tree consisted of three lines of descent (three trunks) for which the term domain was introduced as highest rank of classfication. The three domains were archae, bacteria and Eukarya. These originated by cell division from last universal common ancestor (LUCA). Thus three domain system was introduced based on phylogenetic relationships.

3. Horizontal gene transfer is defined as the transfer of the genetic material between two organisms other than the DNA transmission from parent to their offsprings. It includes:

A) Transformation: it includes the uptake of naked DNA from the environment.

B) Transduction: transfer of bacterial DNA to another bacteria by means of a bacteriophage.

C) Conjugation: transfer of DNA occurs by means of a sexual pilus and there is cell to cell contact.

4.   The endosymbiotic hypothesis deals with the origin of eurkaryotic organelles mitochondria and chloroplast. According to this hypothesis both mitochondria and chloroplast were separate prokaryotic oraganisms that were taken inside primitive eurkaryotic cell. Mitochondria is the result of endocytosis of aerobic bacteria while chloroplast originated as a result of endocytosis of photosynthetic bacteria.

5. PCR stands for Polymerase chain reaction. It is used in molecular biology to amplify a segment of DNA into large number of copies.