Chapter 10 - Nature of the Gene and Genome (Spring 2011)

Address the physical nature of genes during this time

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Unformatted text preview: ddress the physical nature of genes During this time, biologists were studying the physical basis of heredity Physical Carriers of Genes o o o Wherever physical units of heredity came from they had to: be passed on from cell to cell, be passed from generation to generation, and must be contained within a single cell The cytoplasm and its contents divided randomly between daughter cells Nuclear contents divided equally 1 o o o o During cell division, the nucleus organized into visible threads called chromosomes chromosomes are doubled prior to cell division Fertilization observed sperm and egg looked very different but had common chromosomes Chromosomes are presented as pairs of homologous chromosomes Chromosomal behaviour correlates with Mendel s laws of inheritance Chromosomes o o o o o o Genes that are on the same chromosome do not assort independently Genes on the same chromosomes are part of the same linkage group the traits analyzed by Mendel occur on different chromosomes Drosophila (flies) Morgan had wild type flies, but he developed his first mutant This served as evidence for linking chromosomes as gene carriers to evolution He eventually isolated 85 different mutations in 4 linkage groups (flies have 4 chromosomes) He confirmed that genes reside on chromosomes Crossing over and Recombination o o o o o o o o Mendel found that genes controlling different traits segregate independently of each other independent assortment Genes on the same chromosomes act as if they are linked linkage groups But in reality, genes on the same chromosomes did now always act like they were linked they could be inherited separately Linkage between alleles on the same chromosome is incomplete During meiosis homologous chromosomes wrap around each other proposed that this interaction allowed breakage and exchange of chromosome pieces (genes) Morgan called this crossing over or genetic recombination and explained incomplete linkage Percentage of recombination between a pair of genes is constant Percentage of recombination between different pairs of genes can be different suggests position of genes along chromosome is fixed, the position of genes along the chromosome (loci) can be mapped frequency of recombination indicates distance, and increases as the distance increases Chemical Nature of Genes o o o o o o o o Same time Mendel was working, Miescher isolated a new molecule from cell nuclei nuclein, later called nucleic acid Around the same time scientists were studying...
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