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BIOL 239
Christine Dupont

Set 82 If genes on different chromosomes assort independently because of the independent segregation of homologs during meiosis how do genes on the same chromosome assortrecombination is happening in meiosislinkage genes that are in proximity to each other in the same chromosomesMendel didnt notice that He saw traits and genes on different chromosomes so they segregated randomlywhat happens when genes are on the same chromosome It is expected that they will travel togetherlinkage genes and a chainMendel observed in his law of segregation two different traits encoded by two different genesa heterozygous individual is expected to have four possibilitieschromosomes can go in every possible way and match up with each other1111 ratio Equal numberson the same chromosome one chromosome goes to one sideone will be homozygous mutant and the other wild typeif you have two heterozygous individuals and two traits were on different chromosomes the ratio between the heterozygotes will be ratio of one gene two alleles 31two genes crossing heterozygotes is 9331 or some variation of thatif the two genes are on the same chromosomes there wont be a 9331 ratio because those two genes tend to travel together and distribute themselves into the gametes not in a random way3 Some genes on the same chromosome assort together more often than notIn dihybrid crosses departures from a 1111 ratio of F1 gametes indicates that the two genes are on the same chromosomenot completely independent of each othercan see this in the F2 offspringIn other words they are in close proximity to one another and therefore tend to assort togethergenetically linkedif you have a dihybrid you would expect a 1111 ratio in the gametescrossing those will give 9331 in f24 Some genes on the same chromosome assort together more often than notsome genes on the same chromosome are more closely linked than othershow can we tell this What kind of ratios do you geta look at sweet peas5Ratio 24117were making some dihybrids herethe parents are true breedingyou get hetero in f1 simple case of dominant and recessivebreeding in f2 we dont get 9331 We get 9117 Not even close to what we expectedskewing of ratio tells us the genes are linked Theyre on the same chromosome so not behaving as independent units6 Can track genes on chromosomes by looking at F2 offspring of a testcross
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