Fine spines (s), smooth fruit (tu), and uniform fruit color (u) are three recess
ID: 58902 • Letter: F
Question
Fine spines (s), smooth fruit (tu), and uniform fruit color (u) are three recessive traits in cucumbers, the genes of which are linked on the same chromosome. A cucumber plant heterozygous for all three traits is used in a testcross, and the following progeny are produced from this testcross:
This one is a little tricky, so take a good look at the NCOs. Is the phenotype with all 3 recessive traits one of the NCO's? Is the phenotype with all wild type or dominant alleles one of the NCO's? If not, what does this tell you?
Determine the order of genes s, tu, and u on the chromosome.
The middle gene is .
Calculate the map distances between the genes, to the nearest 0.1 cM.
Remember: 0.100 = 10.0% = 10.0 cM = 10.0 mu
Do not write "cM", just the number!
The distance between S and Tu is .
The distance between U and Tu is .
The distance between U and S is .
Determine the interference value to the nearest 0.01.
The interference value is .
Explanation / Answer
Parent genotype = s u tu / S U TU
s U TU / S u tu = Recombinant frequency % of Ss allele = 13%
S u TU / s U tu = Recombinant frequency % of Uu allele = 18.2%
s u TU / S U tu = Recombinant frequency % of TUtu allele = 66%
The double-crossover gametes are always in the lowest frequency.
RF% more than 50% confirms that the gene locus is not on the same chromosome,
Therefore the gene order is S------------------U-------------------TU
31.3mu 79mu
Map unit between TU and U locus = 70+82+13+17 = 182/230x100= 79%
Map unit between U and S locus = 21+21+13+17 = 31.3%
The distance between U and TU is 79 mu
The distance between U and S is 31.3 mu
The distance between S and Tu is 110.3 mu
Interference= 1-coefficient of coincidence
1-0.24=0.75
C.C. values between 0 and 1 indicate partial interference
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