Lecture 6 Flashcards
What are the advantages of a three point test cross?
By using three genes as opposed to two the genome can be more efficiently mapped and double crossovers are not likely to be missed as they would be in dihybrid crosses allowing more accurate map distances to be obtained
How is recombination frequency determined in a trihybrid cross?
Calculate the recombination frequency for each possible pair ignoring the the third trait
What problem could be found with double crossovers when mapping genes with recombination frequencies from trihybrid crosses?
The distance between outside genes is often underestimated as the progeny with double cross overs is the same as the parental type with regards to the outside markers, so they are not included when they should be in the recombination frequency
To account for this we simply multiply the number of double cross overs by two
How can gene order be deduced by inspection?
I there is linkage present then the most frequent combinations will be the parental type while the two least frequent combinations will be the result of double crossovers, this situation we can find that the middle trait will be flipped between these two combinations
What are the effects of multiple crossovers?
Multiple crossovers often go undetected when observing the offspring of genetic crosses causing errors when finding large map distances this can be dealt with either through the use of correcting functions or through inserting more markers
What is the role of interference in recombination?
The expected frequency of double crosovers (calculated by multiplying the recombination frequency of both pairs recombinants) is typically less than the observed number of double cross over recombinants suggesting that crossovers in one region inhibit crossovers in the other region
What is the coefficient of coincidence?
observed number of double crossovers/expected number of double cross overs
How is interference calculated?
1-Coefficient of coincidence=Interference
