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BIO207H5 (42)
Chapter 14

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University of Toronto Mississauga
Karen Williams

Ch. 14: Genetic mapping in Eukaryotes (pgs 410-410) Genes that are on the same chromosome are said to be syntenic -genes that do not appear to assort independently because they are located on the same chromosome exhibit linkage and are called linked genes. These genes belong to a linkage group -genetic analysis is the dissection of the structure and function of the genetic material -progeny showing the parental combinations of alleles are called parentals, and progeny showing nonparental combinations of alleles are called recombinants -the process by which the recombinants are produced is called genetic recombination -Genetic maps are constructed using both gene markers and DNA markers. A marker, or genetic marker, is another name for a mutation or variant that gives a distinguishable phenotype. In other words, it is an allele that marks a chromosome or a gene. -gene marjers are alleles of genes, whereas DNA markers are molecular markers (that is DNA regions in the genome that are polymorphic (differ among individuals) and thus can be detected by the molecular analysis of DNA Early Studies of genetic Linkage: Morgan’s Experiments with Drosophila - see pg 402. Second half of the page. a b / a b …. w m (read how to write these.) -We call the original genotypes of the two chromosomes parental genotypes, parental classes, or parentals. (also used to describe phenotypes) -nonparental combinations of linked alleles are called recombinants - a total of 50% recombinant phenotypes is expected in the case of independent assortment; thus the lower percentage observed is evidence of linkage of the two genes -the closer two genes are on the chromosome, the more likely they are to remain together during meiosis; hence they will not assort independently. The reason is that the recombinants are produced as a result of crossing over between homologous chromosomes during meiosis, and the closer two genes are together, the less likely there will be a recombination event between them - a chiasma is the place on a homologous pair of chromosomes at which a physical exchange is occurring; it is the site of crossing-over. -crossing over is the reciprocal exchange of chromatid segments are corresponding positions along homologous chromosomes; the process involves breakage and rejoining two chromatids -crossing over is also defined as the events leading to genetic recombination between linked genes in both prokaryotes and eukaryotes genetic recombination between linked genes in both prokaryotes and eukaryotes Gene recombination and the role of the chromosomal exchange -physical markers: cytologically detectable visible changes in the chromosomes that make it possible to distinguish the chromosome and, hence, the results of crossing over under the microscope -there is no doubt, therefore, that genetic recombination results from crossing-over causing physical exchanges between chromosomes Cons
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