Model Essay, Research Paper
Question 1: Describe and explain how the following ideas supported the “Discrete Particle of Inheritance.”
a) Principle of Segregation
b) Principle of Independent Assortment
c) Dominant and recessive alleles
d) Statistical analysis and probability
The discrete particle of inheritance model impersonates sexual reproduction through generations of offspring. By manifesting gametes and consolidating them in fertilization a gauche model of what could happen will be produced. The model congregated is not transcendent since mutation is not accounted for during simulation.
The principle of segregation, by Mendel, justifies the discrete particle of inheritance model because it inaugurates the separation of paternal and maternal genes for traits of the offspring. Some genes were dominant and some were recessive. The genes from the predecessors would associate to form traits.
Example:
R=round(Dominant) r=wrinkled(Recessive)
If we combine a RR with a rr 100% of the offspring would have the genotype of Rr and would be round. However, if a Rr and a Rr are combined then: 25% would be RR, 25% rr, and 50% Rr.
The principle of independent assortment also reinforces the discrete particle of inheritance model by presentation of how the separation of male and female genes for different traits are interjected in producing traits for the offspring. This explained how some peas were wrinkled and green and some were round and yellow.
Example:
R=round(Dominant) r=wrinkled(Recessive) Y=yellow(Dominant) y=green(recessive)
If a RRYY is combined with a rryy then 100% of the offspring will have the genotype of RrYy. But if a RrYy is combined with another RrYy then: 25% RrYy, 13% RRYy, 13% RrYY, 13% Rryy, 13% rrYy, 6% RRYY, 6% RRyy, 6% rryy and 6% rrYY.
Dominant and recessive alleles supports the discrete particle of inheritance model because it explains how a trait can disappear in one generation and manifest in the next. Traits do not coalesce into each other, one trait simply surmounts the other in the first generation offspring. This creates the immense diversity of the offspring.
Statistical analysis and probability also supports the discrete particle model of inheritance. Since genes are discrete entities, the observed results of crosses can be scientifically analyzed using statistics and probability. Using observable differences, scientists soothsay what percentage of the offspring should acquire particular traits from their parents.
Question 2: Describe and explain what important experiments and/or findings which lead to answering the following questions:
a) Where were the “discrete particles located?”
b) What are the “discrete particles” composed of?
c) What is the structure of the “discrete particles?”
The establishment of the discrete particles was determined in the experiment of Walter Sutton. Sutton was contemplating meiosis in grasshoppers and scrutinized that chromosomes occur in morphologically similar pairs and that the two members of a chromosome pair segregate from each other during gamete formation. He used this evidence with Mendel’s findings to hypothesize that the hereditary material is associated with chromosomes. Thomas Morgan confirmed this with his experiments on the Drosophila fly. He subjected the flies to radiation and caused mutation of observable traits. With this information Morgan and his students proved genes are chromosomally located.
The uncertainty of what the genes were devised of was answered by Frederick Meischer. He isolated a novel substance from the nuclei of white blood cells. He labeled it nuclein. The nuclein had a eminent concentration of phosphorus but his colleagues aspired to convince him that nuclein was just another protein and phosphorus was a contaminant. Meischer stood by his conjecture that nuclein was another molecule. Eventually chemical analysis proved that chromosomes are made of both protein and Meischer’s nuclein. However, there was a immense disagreement on which molecule, the DNA or the protein carried genetic information. Later experiments by Frederick Griffith and O.T. Avery proved that DNA was the carrier of the genetic information.
Now that is was ascertained that DNA was the source of the genetic code for reproduction the next question was what it looked like. Scientists knew that whoever discovered the structure of the DNA would be infamous. Francis Crick and James Watson are credited with the explanation. Their idea was that DNA was a helix composed of two strands running in opposite directions with internal pairing between the bases, adenine, thymine, cytosine, and guanine. Once presented there was little argument to the find. Everyone knew Watson and Crick had discovered the structure of DNA.
Question 3: Describe the specifics of the original Central Dogma that Frances Crick proposed. Describe what new findings lead to the revision of the central dogma. In describing these new findings, tell why it contradicted the original Central Dogma.
In 1957, Frances Crick described the process of information translation. It was to become comprehended as the central dogma. This process can be best characterized as:
DNA –> RNA –> protein
The information in the DNA is composed of a sequence of nucleotide which is translated into amino acids via the RNA. It’s like mimeographing pages from a publication and having them translated into a extraneous language. DNA was seen as a continuous segment whose linear nucleotide sequence corresponds to a linear sequence of amino acids. However revisions to this speculation came soon after.
Later experiments found that the flow of information from DNA to RNA is not one way. Information can also flow from the RNA to the DNA. They also concluded that inside the DNA existed introns and exons. The introns are excised before the DNA is translated into protein because it does not contain advantageous data. The exons are conserved and translated. These introns and exons contradicted the central dogma because it was believed that all DNA is functional. For the same reason “Junk” DNA or sections of DNA that reiterate over and over like a marred record breaks the central dogma. They are called junk because scientists don’t know why they exist but they do believe they serve a purpose. “Jumping genes” or transposons also break the central dogma since they are nucleotide sequences in a gene that don’t stay put but they hurdle around on the DNA strand. However, the most intriguing discovery was that RNA, like an enzyme, has the ability to catalyze chemical reactions. Before this discovery it was believed that the RNA was just a passive middleman between the “real” molecules. This made it possible to explain the origin of life on Earth and the evolution of nucleic acid and proteins.
Question 4: Based on your reading, evolution depends on two interrelated processes:
The creation of genetic variation
The selection of certain variants
Describe and explain the mechanisms that create genetic variation in organisms that reproduce sexually and in organisms that reproduce asexually.
Since genetic variation drives evolution, nature has many mechanisms for generating genetic variation. All of these mechanisms are commonly congregated into two broad categories: mutation and recombination.
Mutations are changes in the genetic information a cell carries. Some mutations are beneficial, others are catastrophic and many are neutral. The larger the amount of genetic information that is modified usually makes it more likely to be detrimental.
Deletions and duplications are types of mutation. Deletions occur when a chromosome is lost. When this happens the individual is often sterile which prevents the mutation from infiltrating the gene pool. Gene duplication can be advantageous if it results in an increased production of a protein that contributes to the survival of the individual.
A special form of mutation that occurs in both prokaryotes and eukaryotes involves transposable elements or “jumping genes.” These elements are short segments of DNA that include a gene that causes it to transpose or jump to a new location on the DNA strand. Sometimes the jumping involves a new copy of the transposon and sometimes it doesn’t. Gene jumping can be devastating to an individual if it jumps into the middle of an important gene and alters the nucleotide sequence within the gene. This could prevent the synthesis of the gene. To date, scientists have discovered transposons in plants, animals, yeasts and bacteria.
Recombinations are the joining of genetic information from two sources to produce new genetic combinations. It differs from mutation because the genes are not altered but simply reassorted. Exactly how the genetic material from two sources gets combined varies with the mode of reproduction of the organism.
For almost all organisms that reproduce sexually, reproduction involves two processes:
The production of gametes and the fusion of the gametes. Recombination occurs during both processes.
During fertilization the gametes fuse and the resulting zygote’s genetic information is a new combination of the information from the two parents. The offspring that is produced from this zygote has genetic information from both parents and can not be genetically identical to either parent. Any trait that one parent contains could easily end up within the child.
During gamete formation recombination also occurs as a result of the independent assortment and segregation of nonhomologous chromosomes and the crossing over that occurs between homologous chromosomes. As a result of independent assortment and segregation each gamete produced contains genetic material from maternal and paternal sources and in new combinations. The number of homologous chromosomes that could be generated in the production of each human gamete is more than eight million. In the pairing of homologous chromosomes, genetic material from the paternal chromosome is exchanged with the genetic material of the maternal chromosome via the process of crossing over. The resulting chromosome is a hybrid of genes from both sources.
In asexual reproduction a cell makes an exact genetic copy of itself. The offspring are called clones of the parent. The group resulting from repeated reproduction is known as a clonal population because every member is identical to every other member. There are three ways in which genetic materials from two sources can be combined: conjugation, transformation and transduction.
Conjugation is the direct transportation of genetic information between cells. Two cells are drawn together by the pilus of the fertile cell. Then a copy of the fertility factor is transferred to the recipient cell. The result is two fertile cells.
In transformation a new combination of genetic material is created when cells take up DNA from the medium around them. Cells that are able to do this are known as competent.
Finally, in transduction a phage or a virus injects nucleic acid into a host cell where it is replicated into viral coat proteins. The viral nucleic acid is packaged into the new virus coats and new virus particles are released.