Chapter 06

Chapter 06 - Chapter 6 Genetic Recombination in Eukaryotes...

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Chapter 6 Genetic Recombination in Eukaryotes Overview •In meiosis, recombinant products with new combinations of parental alleles are generated by: –independent assortment (segregation) of alleles on nonhomologous chromosomes. –crossing-over in premeiotic S between nonsister homologs. •In dihybrid meiosis, 50% recombinants indicates either that genes are on different chromosomes or that they are far apart on the same chromosome. •Recombination frequencies can be used to map gene loci to relative positions; such maps are linear. •Crossing-over involves formation of DNA heteroduplex. Recombination (1) •A fundamental consequence of meiosis –independent assortment (independent segregation) –crossing-over between homologous chromatids •Yields haploid products with genotypes different from both of the haploid genotypes that originally formed the diploid meiocyte Recombination (2) •Bringing together of two or more pairs of alleles into new combinations Independent assortment (1) •Also known as independent segregation •Consequence of independent alignment of chromosomes in meiotic bivalents Independent assortment (2) •For genes on different (nonhomologous) pairs of chromosomes, recombinant frequency is always 50% Dihybrid testcross (1) Determines genotype of dihybrid by crossing to homozygous recessive tester Dihybrid testcross (2) •Best way to study recombination is in a dihybrid testcross –only dihybrid produces recombinant genotypes –all homozygous recessive tester gametes alike •Typical 1:1:1:1 ratio a result of independent assortment in dihybrid •Each genotype in progeny has unique phenotype •Observed by Mendel in testcrosses with two pairs of traits Dihybrid selfing •Cross between two A/a ; B/b dihybrids –recombination occurs in both members of cross
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This note was uploaded on 09/21/2009 for the course MCB 5896 taught by Professor Zhang during the Spring '08 term at UConn.

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Chapter 06 - Chapter 6 Genetic Recombination in Eukaryotes...

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