Astronomy 5 — Homework Assignment #5 Due on Friday, May 8, at 11:59 PM 1. a) Explain briefly how horizontal gene transfer has probably provided a tremendous boost to the rate at which evolution has...

1. a) Explain briefly how horizontal gene transfer has probably provided a tremendous boost to the rate at which evolution has taken place on the Earth.
In the initial stages of prokaryotic evolution, it was thought the rate of HGT was quite high. This resulted in absence of separate lineages of organisms. Lineages with their own specific or discrete set of genes emerged later on, when the rate of HGT slowed down substantially. This is popularly known as the Darwinian Threshold.
Many studies indicate that the transfer can happen both among and between domains in all possible directions as shown below.
Bacteria Archaea, Archaea Bacteria, Archaea Eukarya, Bacteria Eukarya, Eukarya Bacteria and possible within Eukarya also. The transfer between Bacteria Archaea is the most accepted of all transfers.
A persistent question related to the prominence of horizontal gene transfer in evolution is related to the genes in any given organism have been acquired by horizontal gene transfer. Nevertheless, its significance as an evolutionary mechanism can be inadequate if only a few horizontal gene transfer events have occurred in the history of life.
It is estimated that the number of genes of each microbial genome have been acquired by horizontal gene transfer between 1.6 and 32.6 per cent of the total genes.
In a research by Dagan et al. (2008) using a network analysis of shared genes in 181 sequenced prokaryotic genomes shows that this increases dramatically to 81 ± 15 per cent if the cumulative effect of HGT is taken into account, the significance of this phenomenon in microbial evolution can be understood.
HGT in eukaryotic evolution would be of more importance if we consider animal and plant hybridization a massive horizontal gene transfer event, and the anticipated role of hybridization in evolution, as well.
b) Consider the following statement: “Horizontal gene transfer is the primary reason for bacterial antibiotic resistance.” Explain why this is likely to be true.
(Note: horizontal gene transfer, also known as lateral gene transfer, will be discussed in lecture and in the textbook, but is more widely discussed at an accessible level in many places online.)
When penicillin, the first antibiotic was discovered, many thought this might lead to the elimination of illness. This anticipation did not come true. After the discovery of DNA (genetic code), it was understood that some bacteria were resistant to antibiotics. The reason being presence of genes that made the bacteria unaffected to the action of antibiotics.
Populations hold genetic variation that permits the survival of some individuals of the population when faced with evolving environmental conditions. Genetic variation is the repurcusion of mutations in coding regions of DNA. By introducing antibiotics into bacterial colonies, their biological fitness and the recurrence of antibiotic resistant genes in bacterial populations has been increased. HGT permits novel variants to arise without a mutation in that variant. On the top of it, due to natural selection the antibiotic resistance increases and bacteria can obtain genetic material through HGT. DNA plasmid and a transposon are the two forms of receiving genetic material. A transposon is genetic material from one organism that gets imbibed into the DNA of another organism, while plasmids are not incorporated into the DNA of the host organism. This is how the bacteria receive extracellular genes. HGT is responsible for the spread of antibiotic resistance through the exchange of genetic material across genera. This results in increase probability of formation of a more harmful and antibiotic- resistant bacteria. Though effective initially, repeated and unnecessary usage of antibiotics by humans results in a selective pressure to increase the frequency of antibiotic resistance genes. After treatment, the remaining microbes have a greater chance of possessing a resistance gene.
2.What is a cellular organelle? List 5 different organelles that a cell might possess, and indicate the function of each. Also, specify which of these organelles...