Genetics Chapter 1 Homework Essay

1. Define genotype and phenotype, and describe how they are related.

Genotype is the genetic make-up, the inheritable information, which comprises an individual organism. It is the code that is copied in reproduction and is passed from 1 generation to the next. It serves as the main guide in the growth, development and maintenance of a living organism; it also controls the formation of certain proteins and regulation of metabolism and synthesis. Alleles are alternative forms of a gene and genotype refer to a specific allele like hair color, height, skin tone, etc. These observable traits are the phenotype. Phenotype is the resulting characteristic of an encoded genotype; it is what we can see, it’s the physical appearance of an organism. Genotype defines what will be the phenotype. 1Say for example, eye color. This is controlled by a single gene, but with several alleles.

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Example:

Phenotype
Genotype; Allele
Dominant Trait- B
Brown Eyes
BB. Bb
Recessive Trait-
Blue Eyes
bb

The dominant trait means that whenever there is a copy of B, then this trait will be observable in the organism. Meaning, if one has an allele of either BB, his genotype will be homozygous dominant, therefore, his phenotype will be brown eyes. It can be concluded that phenotype is directly relevant to the genotype of an individual. Genotype is the code that defines what the phenotype will be.

5. Given the state of knowledge at the time of Avery, Macleod, and McCarty experiment, why was it difficult for some scientists to accept that DNA is
the carrier of genetic information?

Avery and his colleagues conducted a study to prove that DNA was indeed the carrier of the genetic data, not protein, as most scientist of that time would assume. Streptococcus pneumoniae, also called pneumococcus, was the subject of Avery’s experiment. These non-virulent bacteria had 2 types that do not convert spontaneously among each other, but when injected to a mice died. This transformation from a non-virulent bacteria to a virulent bacteria was where they centered the idea of their experiment; they effectively isolated the transforming agent from the bacterial cells. They remove the proteins from the bacteria then tested the presence of DNA. Finally, immunological tests involving centrifugation and electrophoresis were performed, which also showed that proteins and polysaccharides weren’t present, but that DNA was. From this summary, it can be observed that a thorough experiment was performed, however, Avery had doubts that the DNA was the gene. In his conclusions, it was not stated that he was certain that what transformed the bacteria is the DNA. Although it may seem that Avery and his colleagues had proven that DNA was the site of the gene, this was not entirely the case. There was still a possibility that, as Avery puts it in the manuscript, “the biological activity of the substance described is not an inherent property of the nucleic acid but is due to minute amounts of some other substance adsorbed to it or so intimately associated with it as to escape detection…” Also, his study was easily questionable to be limited to only bacteria. 2

6. Contrast chromosomes and genes.

Chromosomes are thread-like organized structure composed of protein and a single piece of DNA. In this DNA are where genes are located. Genes are the working subunits of DNA. Each gene contains a particular set of instructions, usually coding for a particular protein or for a particular function. Chromosomes on the other hand are those formed by the coiling of DNA containing the genes. With that said, genes are only a part of a chromosome; chromosome are where genes are found.

8. Describe the central dogma of molecular genetics and how it serves as the basis of modern genetics.

Central dogma forms the backbone of molecular biology. In 1958, Francis Crick enunciated the “central dogma of molecular biology.” This scheme outlined the residue-by-residue transfer of biological information as encoded in the primary structure of the informational biopolymers, nucleic acids, and proteins. It is the step by step of how the genetic information flows within a biological system. The predominant path of transfer is as shown below:

Cells are basically governed by a this molecular chain of command

It involves 3 fundamental processes: replication, transcription, and translation.
It serves as the basis of modern genetics because being termed as the “central dogma,” it gives the basic summary of the process of gene expression; this flow of information from DNA to RNA to protein is descriptive of all organisms with the exception of some viruses that have RNA as a repository of their genetic information. 3

14. How has the use of model organisms advanced our knowledge of the genes that control human diseases? Statistically the average life expectancy of all people in the world is currently 66.26 years (64.3 years for males and 68.35 years for females). 4 If humans will be used as testing samples for experimental procedures, aside from ethical implementations, it will take up too much time to study. A scientist who started to conduct the research might not even live long enough to gather sufficient information. Also, the human system is too complex and samples won’t be readily available for research. The use of model organisms aided these problems. A model organism is an animal, plant or microbe that generally grow quickly, are relatively simple and inexpensive to work with, and are widely available for use in experiments, and can be used to study certain biological processes.5 Being simpler than the very complex system of human beings, these models made it easier for scientists to manipulate, to test, to research on something that is fairly in relation with the human system. This common evolutionary
heritage makes it possible to use genetically tractable organisms to model important aspects of human medical disorders such as cancer, birth defects, neurological dysfunction, reproductive failure, malnutrition, and aging in systems amenable to rapid and powerful experimentation.

Certain examples are:
Experiments performed with yeast have also clarified how genes are turned on or off. This knowledge explains how cells that contain the same genes can be so different from one another, which has advanced understanding of both normal developmental processes and diseases that occur when genes are turned on or off at the wrong time or in the wrong cell.

Studies in fruit flies and tiny worms taught scientists key aspects of how fertilized eggs develop into complex organisms. In the course of these studies, researchers made unanticipated discoveries, such as learning that genetically controlled cell death plays a critical role in cancer and other diseases.

Research with bacteria, viruses and yeast has revealed how all living things pass on their genes to offspring through copying DNA and fixing mistakes that get made during the copying process.

Laboratory rats have been used for many decades to test drugs. In addition, much of what we know about cancer-causing molecules was learned through basic research with rats. 6

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