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Genetics Questions, Essay Example

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Essay
  1. Compare and contrast binary fission, mitosis, and meiosis. Please include a discussion of their prevalence within their domains of life and the advantages/disadvantages for each approach of cell division.

Cells can divide. In unicellular organisms, this makes more organisms. In multicellular organisms this is used for growth, development, and repair.

Binary fission is the asexual reproduction of a cell which only takes place in prokaryotes. Before this can occur, a cell must replicate its chromosome. This starts when a replication bubble opens within the DNA. There is normally only a single origin of replication, unlike that of Eukaryotes. As the bubble increases in size, the DNA strands become longer. DNA polymerase converts each of these strands into double strands and two circular chromosomes are produced. They then affix to the cell membrane, move apart, and pass into each of the daughter cells.

Mitosis is the process of division of chromosomes. There are five stages in the process. Interphase is the resting phase, however, at this stage replication of chromosomes and cell growth are still taking place. In prophase the chromosomes start to coil, shorten and become distinct. The mitotic spindle also starts to form. In animals, centrioles begin to move toward the poles of the cell. In metaphase, the chromosomes begin to line up along the equator of the cell. In anaphase, the chromatids separate at the centromeres and are pulled to the poles of the cell. Telophase takes place when the new daughter nuclei and nuclear envelopes start to reform and chromosomes uncoil. This is also the start of cytokinesis. Cytokinesis happens only in mitosis. In animals it happens in the cleavage furrow and in plants it happens in the cell plate.

The significance of cell division in mitosis and binary fission is that they produce two cells that are identical to the parent cell. In unicellular organisms, this is asexual production. In multicellular organisms these processes help with growth and repair and asexual reproduction.

Meiosis is present in sexual reproduction. Again meiosis goes through the same phases as Mitosis, but there are multiple of each phase. The phases do differ somewhat.

The differences between mitosis and meiosis are that meiosis occurs in germinal tissues. Meiosis involves two successive nuclear divisions in which the chromosomes are duplicated only once. The two divisions are termed meiosis one and meiosis two, which explains why there are multiples of each stage in the process. At the completion of meiosis there are four daughter cells, instead of two like that of mitosis. The daughter cells are genetically different due to crossing over and independent assortment, unlike in mitosis and binary fission where the daughter cells are identical.

  1. Describe the two laws of inheritance for diploid species. Describe the process and assumptions that lead to these two laws.

The two laws of inheritance were derived by Gregor Mendel while he was experimenting with pea plants in the 1800’s. While crossing purebred white flowering plants with purple flowering plants, he discovered that a purple flowering plant was produced. This led him to conceive the idea of heredity units or factors as he called them. He stated that each individual has two factors for one trait, one factor from each parent. This is where he started to conceive the notions of dominant and recessive traits.

The first law is the law of segregation. This law states that each individual possesses a pair of alleles for any trait. Each parent passes a randomly selected copy of one of these to its offspring. Whichever allele is dominant expresses that trait in the offspring.

The second law is the Law of Independent Assortment. This law states that separate genes for separate traits are passed independently of one another from parents to offspring. Different traits are inherited independently from each other so for example, there is no relation between eye color and hair color.

  1. Provide three independent reasons why human females have the greatest influence on the phenotype of their offspring.

The first reason is that females more energy into producing offspring, according to the Bateman’s principle. A female’s ability to reproduce is dependent on how many eggs she produces, rather than how many males she mates with. This results in sexual selection, in which she is picky about which males she mates with.

Another reason that females have a greater influence on phenotype is that they are responsible for prenatal care. The female carries the child until birth. They are responsible for what the offspring are exposed to within the womb. This can lead to differences based on exposure.

Another reason that females have a greater influence on phenotype is that when a mother is pregnant, the male set of genes can be seen as a foreign intrusion within the body that the body tries to fight off like an infection. The set of genes from the mother is trying to produce a successful pregnancy which could be why the mother has greater influence.

  1. Discuss why the traditional terms dominance and recessive can be misleading concepts. Provide three examples where these terms are misleading.

When speaking of dominant and recessive traits dominant means that it is more likely to succeed where as recessive means that this trait would be more likely to hide. This can be misleading because that is not always the case. Offspring receives an allele from each parent. Each parent could carry a dominant and recessive trait for a particular trait. If the offspring receives the recessive trait from each parent, then that recessive trait will be present rather than the dominant trait.

There are many examples of this. The first is eye color. If one parent has blue eyes and the second has brown eyes it would seem that offspring would have brown eyes because the blue eye trait is recessive. However, if the brown eyed parent carries the recessive trait for blue eyes, it could be that offspring will have blue eyes.

Blood type is another example. The A blood type and the B blood type are both dominant, but the O blood type is recessive. If one parent has an A blood type and the other parent has the B blood type, how is the dominant trait determined. It would be completely up to chance as to what blood type would actually be dominant in this matter, which can be misleading in that we are often taught that there can only be one dominant trait.

Another example that can be confusing is dwarfism. Dwarfism is actually a dominant trait, whereas the normal growth allele is recessive. There are far more people who have show the normal growth allele, than the dwarfism allele. It is still possible for two normal people to have offspring that suffer from dwarfism. Apparently the parents must carry the dominant trait in a recessive way for this to happen.

Recessive and dominant are not as clear and concise as many people deem them to be. There are many instances in which a dominant trait may not appear in a second generation; however it appears again in a third generation.

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