The formula for mapping the distance between two genes in unordered tetrads is:
ID: 88553 • Letter: T
Question
The formula for mapping the distance between two genes in unordered tetrads is: RF=(([Tetratypes] + 6*[Non-parental ditypes])/[Total Tetrads]) * 0.5 Explain how we derived the equation. What is a tetratype? What is a ditype? What is a non-parental ditype? What are the ways that you can produce a tetratype? What are the ways that you can get a parental ditype? What are the ways that you can get a non-parental ditype? How would you estimate the number of meioses that have a single crossover occurring? How do you estimate the number of meioses that have double crossovers occurring? How would you estimate the total number of cross overs that occurred in your sample? Divide the number in v. with the total number of tetrads. What does this number represent? What do we need to multiply this number by 0.5 to get a RF?Explanation / Answer
I) A tetratype is a retread that contains four genotypes of which two contain the parental genotype and two contain the recombinant types. A parental di type is the one that is seen in ascomycetes where both the genotypes seen are parental. Hence, they are called the di types. Here, the spore arrangement would contain only the parental type or the non recombinant types. The non recombinant di type contains only recombinant type of the ascopores, containing the non parental combinations.
2) The tetras are produced by meiosis or meiotic divisions. The parental ditype and the non parental ditype as well as the tetratype are produced by the segregation of the tetrad formed. This segregation occurs if there is a mutation in this tetrad formed by this tetrad.
3) if a single cross over is occurring in a individual with three genes, we would observe that one of the three genes is heterozygous from the other two genes. Example : if the genes are G R W, then on a single cross over, the genes would be either, g R W or G r W or G R w .
iv) the double cross overs would be in the form of g R w or g r W or G r w.
The mapping of these crossovers can be done by calculating the genetic distances between these genes.
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