1. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Chapter 10: Gene & Genome Objectives Early genetic principles (Mendel). Crossing over (recombination) and linkage. Structure of the DNA double helix. DNA supercoiling and topoisomerases Genome complexity and repetitive DNA. DNA denaturation, renaturation, hybridization DNA sequence function Mechanisms for gene duplication Mobile DNA and consequences of transposition Restriction Enzymes, RFLPS, Genome Maps

2. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Genetic Principles Genes, Chromosomes, Recombination, and Inheritance

3. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Figure 10.1

4. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Mendel and Peas Easily defined characteristics (phenotypes) Focused on 7 clearly definable traits, height & flower color, Each trait had 2 alternate & clearly identifiable forms Inbred (purified) lines

5. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Mendel's conclusions Characteristics governed by units of inheritance (genes) Each organism has 2 copies of gene The two genes ( may be same or not - alleles) Dominant alleles mask recessive alleles Gametes have only 1 copy of gene Law of Segregation - alleles separate (segregate) randomly Law of Independent Assortment – true for 2 or more genes

6. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Discovery of chromosomes (colored bodies, 1888) Walther Flemming, early 1880s – –During cell division, nuclear material organized into visible threads called chromosomes –Chromosomes appear as doubled structures, split, then doubled before next division

7. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Fertilization and meiosis Sperm & egg are very different cells Sperm & egg equally important genetically Most obvious shared character: nuclei Theodore Boveri (German) - sea urchin polyspermy –Results in disruptive cell division & early death –Daughter cells receive variable numbers of chromosomes –Each chromosome possesses different qualities Edouard van Beneden (Belgian, 1883)

8. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Fertilization and meiosis Edouard van Beneden (Belgian, 1883) –Discovered Ascaris eggs & sperm had 2 chromosomes each –Somatic cells had four chromosomes August Weismann (German biologist, 1887) –meiosis involved reduction division where chromosome number was cut in half before forming gametes –If not, chromosome number would increase with every succeeding generation

9. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Chromosomes as genetic information Walter Sutton (Columbia, 1903) –Studied grasshopper sperm formation –Saw 2 types of division by spermatogonia –Mitotic divisions where spermatogonia make more spermatogonia –Meiotic division where spermatogonia differentiate into sperm –11 homologous chromosome pairs (look alike) & extra (X) –Correlated with Mendel's inheritable pairs of factors –Hypothesized chromosomes have Mendel's factors –First meiotic division separated pair members

10. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Figure 10.3

11. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Chromosomes as linkage groups How did Mendel's factors assort independently? –Mendel owed his results to good luck or lack of interest in traits that did not fit his predictions –All Mendel’s traits were unlinked or nearly so, but… –Flower color & pollen shape on same chromosome –Crossing over (more later)

12. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Drosophila Genetics– T.H. Morgan Fruit flies were ideal for genetics –Short generation time (14 days) –Produce up to 1000 eggs in a lifetime –Small; easy to maintain & breed; inexpensive

13. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Figure 10.5

14. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Drosophila Genetics– T.H. Morgan by 1915 he found many mutants (85) –Localized to 4 linkage groups, one with few mutants –On rare occasions, mutation occurred –Mutation + Selection = Evolution –Mechanism for new species to slowly emerge –Linkage groups = chromosome pairs (4), one small

15. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Crossing over & recombination F. A. Janssens (1909) –observed interaction of homologs –hypothesized breakage & exchange of pieces Morgan (1911) – this could explain recombination Crossing over makes linkage incomplete Can separate genes on same chromosome Can reshuffle genes –recombination percent constant for given gene pair –but different between different gene pairs

16. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Figure 10.7

17. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Crossing over & recombination Therefore position (locus) of genes fixed –Recombination percentage is a measure of distance –Bigger distance means more crossovers –Big distance = independent assortment –Small distance = tightly linked Alfred Sturtevant (1911) –realized recombination could be used to map –constructed maps of the 4 fruit fly chromosomes –since used to map genes in many organisms

18. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Mutagenesis & giant chromosomes Mutants valuable for genetic analysis Herman Muller (Indiana U., 1927) –Genetic material can be damaged by X-rays –Sublethal dose raises mutation frequency >100 fold –Other mutagenic agents: UV irradiation, ENU

19. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Mutagenesis & giant chromosomes Theophilus Painter (U. of Texas, 1933) –Rediscovers Drosophila polytene chromosomes –Arise in salivary gland cells; Strands stay in register –As much as 1,024 times normal copy number –Cell stops dividing, but keeps growing –Allows cell to maintain high rate of secretion –Exhibit constant banding patterns (~5000 bands) –Bands correlate with specific genes Visualize Deletion by X-rays Visualize species specific evolutionary change Active genes puff out (RNA Synthesis)

20. Copyright, ©, 2002, John Wiley & Sons, Inc.,Karp/CELL & MOLECULAR BIOLOGY 3E Figure 10.8a