Genetics - Analysis and Principles

Biology

Quiz 8 :

Variation in Chromosome Structure and Number

Quiz 8 :

Variation in Chromosome Structure and Number

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Describe the steps you would take to produce a tetraploid plant from a diploid plant.
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Polyploidy is advantageous in plants as this condition enhances the useful traits that can be exploited for commercial farming. The useful traits that are enhanced by polyploidy include the bigger size, the resistance to adverse biotic and abiotic factors and increased metabolite production. Haploid plants can be used to produce tetraploid varieties by physical and chemical mechanisms, as follows:
Exposure of the newly developing plants to temperature shock induced polyploidy. This is achieved by inducing a sudden change in the temperature in which the target plants are developing.
Colchicine is a spindle poison and interferes with the formation of spindle fibers during mitosis. Thus, as the spindle fiber formation is interfered with, chromosomes do not segregate into the daughter cells equally, leading to nondisjunction. At higher concentrations, colchicine can also induce the nondisjunction of entire sets of chromosomes. Thus, colchicine can be used to produce tetraploid plants that are homozygous for all genes in a series of steps.
One other method to produce tetraploid plants from a haploid parent material is by fusing cells. The cell hybridization can be achieved by chemical or physical fusogens such as polyethylene glycol or electroporation respectively. Fused cells form hybrids with the chromosomal complement from each of the parental cell types, known as the 'heterokaryon'. Thus, cell hybridization techniques can be used to produce tetraploid plants from homozygous parents in a series of steps.

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Cell biology textbooks often discuss cellular proteins encoded by genes that are members of a gene family. Examples of such proteins include myosins and glucose transporters. Look through a cell biology textbook and identify some proteins encoded by members of gene families. Discuss the importance of gene families at the cellular level.
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Gene families are those genes that are closely related and have developed from a common ancestral gene in the course of evolution. There are several cellular proteins encoded by gene families, especially in the life forms that occupy the higher levels of the evolutionary tree. Myosins, globins and glucose transporters are a few examples for groups of proteins that are encoded by gene families.
A few more examples of the gene families are the immunoglobulin superfamily, the major histocompatibility complex, the G-proteins gene family, and the myosin gene family.
The proteins of some of the gene families are tabulated below:
img The gene families are important at the cellular level as they can perform more functions with subtle differences when compared to a single gene product. Also, the protein product of each of the genes in a family can be differently expressed based on the need or on the stage of development.

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What is a gene family How are gene families produced over time With regard to gene function, what is the biological significance of a gene family
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A gene family is a group of two or more genes that were produced by a duplication of a single ancestral gene.
Gene families are produced over time as the duplicated genes are present grouped together and are inherited. Each of the genes in the gene family might even accumulate mutations, thus forming closely related gene families over timE.Certain gene families have biological significance in terms of gene functions. Paralogs are the genes of a single species and are as a result of the gene family formed by a single ancestral gene. Such clusters of genes that form a gene family can bring about an important function, contributing to the evolutionary process. An example of such a gene family is the globin gene family. While the ancestral gene would have expressed only one type of globin molecule, thus performing one function, the formation of the globin gene family resulted in the production of several globin molecule types, each with a distinct function. Thus, the formation of a gene family can result in complex functions as can be important for the evolutionary development.

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An inversion heterozygote has the following inverted chromosome: img What would be the products if a crossover occurred between genes H and I on one inverted and one normal chromosome
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Describe how colchicine can be used to alter chromosome number.
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Besides the ones mentioned in this textbook, look for other examples of variations in euploidy. Perhaps you might look in more advanced textbooks concerning population genetics, ecology, or the like. Discuss the phenotypic consequences of these changes.
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A chromosome involved in a reciprocal translocation also has an inversion. In addition, the cell contains two normal chromosomes. img Make a drawing that shows how these chromosomes will pair during metaphase of meiosis I.
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What is the main goal of comparative genome hybridization Explain how the ratio of green to red fluorescence provides information about chromosome structure.
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Following a gene duplication, two genes will accumulate different mutations, causing them to have slightly different sequences. In Figure 8.7, which pair of genes would you expect to have more similar sequences, 1 and 2 or 1 and 2 Explain your answer. FIGURE 8.7 The evolution of the globin gene family in humans. The globin gene family evolved from a single ancestral globin gene. The first gene duplication produced two genes, one that encodes myoglobin (on chromosome 22) and a primordial hemoglobin gene that duplicated several times to produce several -chain and -chain genes, which are found on chromosomes 16 and 11, respectively. The four genes shown in gray are nonfunctional pseudogenes. img
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With regard to the analysis of chromosome structure, explain the experimental advantage that polytene chromosomes offer. Discuss why changes in chromosome structure are more easily detected in polytene chromosomes than in ordinary (nonpolytene) chromosomes.
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Which changes in chromosome structure cause a change in the total amount of genetic material, and which do not
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Let's suppose a researcher conducted comparative genomic hybridization (see Figure 8.9) and accidentally added twice as much (red) DNA from normal cells. What green-to-red ratio would you expect in a region from a chromosome from a cancer cell that carried a duplication on both chromosomal copies What ratio would be observed for a region that was deleted on just one of the chromosomes from cancer cells Figure 8.9 The use of comparative genomic hybridization to detect deletions and duplications in cancer cells. Starting materials: Breast cancer cells and normal cells. img
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What are some experimental advantages of cell fusion techniques as opposed to interbreeding approaches
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Two chromosomes have the following order of genes: Normal: A B C centromere D E F G H I Abnormal: A B G F E D centromere C H I Does the abnormal chromosome have a pericentric or paracentric inversion Draw a sketch showing how these two chromosomes would pair during prophase of meiosis I.
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Discuss how variation in chromosome number has been useful in agriculture.
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How does a chromosomal duplication occur
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It is an exciting time to be a plant breeder because so many options are available for the development of new types of agriculturally useful plants. Let's suppose you wish to develop a seedless tomato that could grow in a very hot climate and is resistant to a viral pathogen that commonly infects tomato plants. At your disposal, you have a seed-bearing tomato strain that is heat-resistant and produces great-tasting tomatoes. You also have a wild strain of tomato plants (which have lousy-tasting tomatoes) that is resistant to the viral pathogen. Suggest a series of steps you might follow to produce a great-tasting, seedless tomato that is resistant to heat and the viral pathogen.
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In agriculture, what is the primary purpose of anther culture
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Explain why small deletions and duplications are less likely to have a detrimental effect on an individual's phenotype than large ones. If a small deletion within a single chromosome happens to have a phenotypic effect, what would you conclude about the genes in this region
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An inversion heterozygote has the following inverted chromosome: img What would be the products if a crossover occurred between genes H and I on one inverted and one normal chromosome
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