04BIS10110152013RecombinLect4

For h re aso n m a es a e a w ay s u e d do ac ve eo

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Unformatted text preview: 2433 VESTIIGIIAL VEST G AL +vg//prrvg +vg p vg 270 270 PURPLE PURPLE prr+//prrvg p + p vg 270 270 5849 5849 Notte:: Allttthough crrosssoverr off non-siistter chromattiids (chiiasma)) iis observed durriing sperrmattogenessiis iin malle N o e: A h ough c o s sove of n on- s s e r c hro ma ds ( ch a sma s obser ved d u n g spe m a oge ne i s n ma e n co a ed m m Drrosophiilla,,, acttuall crossiing overr orr rrecombiinattiion does nott occurr. Forr tthiiss rreasson,,, mallles arre alllways ussed o sop h a ac u a cross n g ove o e com b na on does no o ccur. For h re aso n m a es a e a w ay s u e d Do ac ve eo na m a w e as tthe "ttester" iin a ttesstt crosss.. a s h e " ester " n a e t crosss h " er o BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 20 Mapping Genes on Chromosomes ­ Since the breakage-reunion events (crossovers ) between Since two loci on non-sister chromatids are “independent events”, it follows that the probability (p) of a crossover occurring will be follows of related to the distance between the two loci. As shown below, there are more potential crossovers sites between loci B and C than between A and B. Therefore a map based on recombination frequency (RF) should be higher (i.e., more recombination map units — m.u.) between loci B and C than A and B. m.u. between A B C a b c An odd number of crossovers is needed to recombine loci BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 21 Relationship between RF and Gene Distance BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 22 Double Crossovers involving 3 loci ­ ­ In the example below, a trihybrid cross is performed In trihybrid involving three loci; vestigial (v), cut (ct) and crossveinless involving and (cv). A double crossover occurs between v and cv. Note that c...
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