In tomatoes, the following three recessives are known to occur: r = flattened fr
ID: 163974 • Letter: I
Question
In tomatoes, the following three recessives are known to occur: r = flattened fruit; h = hairy fruit; and f = many flowers/cluster. All three loci are located on chromosome 2. A trihybrid is testcrossed producing the following offspring: RHF/rhf 73 RHf/rhf 348 RhF/rhf 2 Rhf/rhf 96 rHF/rhf 110 rHf/rhf 2 rhF/rhf 306 rhf/rhf 63 Identify the progeny groups receiving the parental linkage arrangements. Identify the progeny groups corresponding to the double crossovers. Determine the sequence/order of the three loci. Calculate the number of map units separating the loci and construct a chromosome map. Are the parental gametes in coupling or repulsion arrangement? Explain Has interference occurred? If so, calculate the coefficient of coincidence to determine the extent of interferenceExplanation / Answer
c. An easy way to determine the order of the gene is to look for the double crossovers. In a double crossover, the phase of the middle locus is reversed.
The parental types are identified by you to be R-H-f and r-h-F. Also, if RhF/rhf and rHf/rhf are the double crossovers as identified by you, then the order of the gene loci are:
H-R-F or F-R-H
d. The total number offsprings: 1000
To calculation the distance between R and F, consider crosses RHF/rhf and rhf/rhf
= [(63+73)/1000] x 100 = 13.6 map units
To calculation the distance between H and R, consider crosses Rhf/rhf and rHF/rhf
= [(96+110)/1000] x 100 = 20.6 map units
Chromosomal map
H----------------R--------F
20.6 m.u 13.6 m.u
e. The parental gametes are in repulsion phase.
Repulsion phase linkage refers to the linkage between dominant alleles of one or more genes and linkage between the recessive allele of one or more genes. Upon crossing over, each parent contributes to the dominant allele for one or more gene.
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