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Unit 8: The Genetic Consequences of Meiosis

Last updated

May 14, 2022
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- 7.7: Meiosis
- 8.1: Mendel's Monohybrid Crosses

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8.1: Mendel's Monohybrid Crosses
This page discusses Gregor Mendel, an Austrian monk whose experiments with garden peas from 1858 to 1866 established the principles of inheritance. He demonstrated dominance through seed traits and highlighted the re-emergence of traits across generations, formulating key hypotheses about heredity. Despite being initially overlooked, Mendel's work is foundational to modern genetics, which has since identified exceptions to his principles of dominance and segregation.
8.2: Crossing Over and Genetic Recombination in Meiosis
This page discusses the process of crossing over between nonsister chromatids, highlighting the precise exchange of DNA segments to maintain genetic integrity. It emphasizes the importance of this precision in preventing gene loss or mutations, which could result in defective gene products or complete gene inactivity.
8.3: The Evidence of Creighton and McClintock
This page discusses a study by Creighton and McClintock on a corn plant exhibiting a unique chromosomal aberration that allowed for the visual distinction of homologous chromosomes. They analyzed gamete production and kernel types resulting from fertilization, revealing a physical exchange of chromosomes during crossing over.
8.4: Genetic linkage and Genetic Maps
This page discusses Mendel's dihybrid cross in peas, which led to the Rule of Independent Assortment, indicating that gene pairs are inherited independently, especially for genes on separate or distantly located chromosomes. It acknowledges the presence of syntenic traits that still assort independently and highlights the complexities of linkage analysis in corn, where varying recombination frequencies can impact the accuracy of genetic mapping.
8.5: Gene Mapping with Three-point Crosses
This page explains how trihybrid test crosses in corn are more effective than dihybrid tests for determining gene order and physical distances between linked alleles. It discusses the importance of recombination percentages and the impact of double recombinants on mapping accuracy. The text emphasizes that closer allelic intervals lead to more precise genetic maps and outlines the methodology for discerning gene order via rare crossover classes.
8.6: Quantitative Trait Loci
This page discusses Mendel's rules of inheritance and their limitations in explaining continuous human traits like height and weight. It highlights Nilsson-Ehle's 1908 research on polygenic inheritance in wheat, illustrating that traits like kernel color involve multiple gene pairs, leading to variations. This concept aids in understanding human diseases, as multiple genes can interact to influence conditions such as cancer.
8.7: Mapping the Genes of T2
This page discusses the infection process of T2 and T4 bacteriophages on E. coli, which results in cell lysis and the formation of clear plaques. Their lifecycle involves attachment, DNA injection, protein synthesis, and virus release. Mutations affect infection capabilities, providing insights into gene functions and mapping.
8.8: rII Locus of T4
This page discusses the T2 and T4 bacteriophages' role in genetic research on E. coli, highlighting Benzer's study of the rII gene, where he identified around 2000 point mutations. He determined that the smallest mutation units are single base pairs and used deletion mutants for efficient mapping. Benzer's complementation tests revealed two complementation groups in rII, leading to the concept of cistrons as genetic functional units.

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