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Chapter 3 : Genes, Genetics, and Geneticists

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Abstract:

This chapter talks about the demonstration of the discrete-particle model. This demonstration requires the use of separate objects-jelly beans, M&Ms, marbles, or index cards-as genes, and mimic sexual reproduction: produce gametes through meiosis, and join them in fertilization. An ancillary but very important feature of the discrete nature of genes involves not biological inheritance, but the ease with which genetic traits can be scientifically investigated. Once Mendel established that the hereditary material is organized into packets of information that separate from each other during gamete formation, scientists had to localize these particles within the cell. When biologists discuss genes, they sometimes sound as if they are talking about a supernatural force, because: Genes occupy a central place in the study of all biological sciences. The structure of the DNA molecule is so simple and yet so powerful. The mechanism of gene action is so awe inspiring. For almost all organisms that reproduce sexually, reproduction involves two processes: production of gametes that differ genetically from the individual producing them and fusion of these gametes to create an individual that differs genetically from both parents. Genetic variation is crucial to the evolution of life on earth. The pivotal concepts of evolutionary biology are contained in the abbreviated description of evolution: variation, chance, and change. A true understanding of genes, biology, and even biotechnology is possible only if one comprehends and appreciates the role these factors play in driving evolution and shaping life on earth.

Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3

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Image of Figure 3.1
Figure 3.1

Graphical representation of the different models of inheritance: fluid blending and discrete particle.

Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3
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Image of Figure 3.2
Figure 3.2

The Principle of Segregation. Mendel observed that experimental crosses between pea plants with round or wrinkled seeds yielded plants with round seeds in the first generation and a 3:1 mix of plants with round and wrinkled seeds in the second generation. From this result and observations of other characteristics, he inferred that maternal and paternal hereditary information is packaged as discrete particles and that maternal and paternal particles separate from each other during gamete formation.

Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3
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Image of Figure 3.3
Figure 3.3

The Principle of Independent Assortment. By observing the hereditary patterns of two separate traits, seed shape and color, Mendel inferred that during gamete formation, the alleles for one trait segregate independently of the alleles for a trait located on a different chromosome. What would Mendel have seen if the genes for seed color and shape were adjacent on a chromosome?

Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3
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Image of Figure 3.4
Figure 3.4

Discovery of the “transforming factor” by Griffith. The strain of pneumonia-causing bacteria (smooth) is virulent because of a gene that codes for a protective outer covering. A different strain (rough) does not cause pneumonia because it lacks the gene for the protective covering. When nonvirulent bacteria are mixed with heat-killed virulent bacteria, the nonvirulent bacteria are transformed into virulent bacteria. The gene for the protective outer layer moves from the dead smooth bacteria to the living nonvirulent strain.

Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3
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Image of Figure 3.5
Figure 3.5

The experiments of Alfred Hershey and Martha Chase. One group of viruses containing protein labeled with the radioactive isotope S and a second group of viruses containing DNA labeled with the radioactive isotope P infected bacterial cells by injecting their genetic material into the cell. Hershey and Chase separated the viral coats from the bacterial cells and found S in the viral coats and P within the bacterial cells. Viral progeny that resulted from the infection also contained radioactive P. Hershey and Chase thus concluded that the genetic material of the virus was DNA and not protein.

Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3
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Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3
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Image of Figure 3.6
Figure 3.6

The diagram illustrates the complex relationships among genes, the proteins they encode, and observable traits. The path from gene to trait is neither straightforward nor linear. One gene affects many traits, and one trait is the end result of the actions of many genes. Gene products produce feedback and alter the activities of other genes.

Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3
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Image of Figure 3.7
Figure 3.7

Gene changes in cystic fibrosis. Different mutations in the gene that encodes the chloride channel protein have different phenotypic effects.

Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3
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Image of Figure 3.8
Figure 3.8

Diagrams of the four types of chromosomal aberrations, or macromutations. The letters denote genetic loci.

Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3
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Image of Figure 3.9
Figure 3.9

Diagrams of the disruptive effect of a translocation on chromosome pairing in meiosis and the resulting gametes. The parental genotype possesses one normal version of each of the two chromosomes involved in the translocation event. The letters indicate genetic loci. Lowercase and uppercase letters denote different alleles for the same trait. Four of the six possible gametes derived from the parental genotype are nonviable because they do not have a complete complement of genes.

Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3
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Image of Figure 3.10
Figure 3.10

Replicative and nonreplicative transposons.

Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3
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Image of Figure 3.11
Figure 3.11

Crossing over between homologous chromosomes occurs during gamete production. As a result, the gametes differ from each other and from the parental genotype.

Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3
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Image of Figure 3.12
Figure 3.12

Sexual reproduction, genetic variation, and recombination. Genetic variation is created during three stages of sexual reproduction. When gametes are produced, they differ genetically from the parental genotype because they have half the amount of DNA and a random assortment of paternal and maternal chromosomes. During fertilization, genetic material from two sources is combined, creating an offspring that differs genetically from both parents. Finally, during gamete production, crossing over between maternal and paternal (homologous) chromosomes occurs, creating “within chromosome” genetic variation.

Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3
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Image of Figure 3.13
Figure 3.13

Asexual reproduction. Offspring are genetically identical to the parent. Genetic variation is created through mutation.

Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3
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Image of Figure 3.14
Figure 3.14

Bacterial conjugation. Genetic material is exchanged between F and F cells.

Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3
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Image of Figure 3.15
Figure 3.15

Transformation. A cell takes up free DNA from its environment, integrates it into its chromosome, and expresses the encoded products.

Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3
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Image of Figure 3.16
Figure 3.16

Transduction. A virus serves as a conveyer of genetic material from one organism to another. In the example here, the organism is a bacterium, and the virus is a bacteriophage.

Citation: Kreuzer H, Massey A. 2008. Genes, Genetics, and Geneticists, p 73-96. In Molecular Biology and Biotechnology: A Guide for Students, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555817480_ch3
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References

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