In a series of two-point mapping crosses involving five genes located on chromosome II in Drosophila, the following recombinant (single-crossover) frequencies were observed: $$\begin{array}{lc} p r-a d p & 29 \% \\ p r-v g & 13 \\ p r-c & 21 \\ p r-b & 6 \\ a d p-b & 35 \\ a d p-c & 8 \\ a d p-r g & 16 \\ v g-b & 19 \\ v g-c & 8 \\ c-b & 27 \end{array}$$ (a) Given that the adp gene is near the end of chromosome II (locus 83 ), construct a map of these genes. (b) In another set of experiments, a sixth gene, \(d\), was tested against \(b\) and \(p r\) $$\begin{array}{ll} d-b & 17 \% \\ d-p r & 23 \% \end{array}$$ Predict the results of two-point mapping between \(d\) and \(c, d\) and \(v g,\) and \(d\) and \(a d p\)

Step by step solution

01

Examine the given recombination frequencies

First, write down the recombination frequencies for all gene pairs: \((p r-a d p, 29), (p r-v g, 13), (p r-c, 21), (p r-b, 6),\) \((a d p-b, 35), (a d p-c, 8), (a d p-r g, 16), (v g-b, 19), (v g-c, 8), (c-b, 27).\)

02

Determine gene order and distances

Determine the gene order using the given recombination frequencies. The order of the genes should be based on the principle that the sum of the recombination frequencies should be minimized. From the given frequencies, we can begin with \(p r\) as the first gene. There are three distances involving \(p r\): \(p r-a d p\), \(p r-v g\), and \(p r-c\). Since the smallest distance is with \(p r-b\) (\(6\%\)), \(b\) should be the closest to \(p r\). We can arrange the other genes in a linear order by observing distances between them: \(p r - 6 - b - 27 - c - 8 - v g - 19 - a d p - 29 - r g\) The positions of \(d\) are given as: \((d-b, 17), (d-p r, 23).\)

03

Determine recombination frequencies between \(d\) and the other genes

Predict the recombinant frequencies between \(d\) and other genes by observing their distances on the map: Between \(d\) and \(c\): \(d - 17 - b - 27 - c\) Recombination frequency: \(17 + 27 = 44\%\) Between \(d\) and \(v g\): \(d - 17 - b - 27 - c - 8 - v g\) Recombination frequency: \(17 + 27 + 8 = 52\%\) Between \(d\) and \(a d p\): \(d - 17 - b - 27 - c - 8 - v g - 19 - a d p\) Recombination frequency: \(17 + 27 + 8 + 19 = 71\%\) The predicted recombinant frequencies between \(d\) and other genes are: \(d-c\): \(44 \%\) \(d-v g\): \(52 \%\) \(d-a d p\): \(71 \%\).

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