Fine spines (f), smooth fruit (s), and yellow fruit color (y) are three autosoma
ID: 101459 • Letter: F
Question
Fine spines (f), smooth fruit (s), and yellow fruit color (y) are three autosomal recessive traits in cucumbers whose genes 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: 880 fine spines, smooth, fruit 3 smooth fruit 64 wild-type 67 fine spines, smooth fruit, yellow fruit 49 fine spines 887 yellow fruit 46 smooth fruit, yellow fruit 4 fine spines, yellow fruit a. What are the genotypes of the two cucumber plants used in the testcross? b. What conclusion can be made about the arrangement of f and y alleles on the chromosomes in the heterozygous plant? c. Draw a corrected map showing the relative order of genes and the distance between genes.Explanation / Answer
a) The cucumber plant which is heterozygous for all the three traits are used in the test cross. Therefore, the genotype of the plants used in test cross are FfSsYy.
b) The offsprings with least number are the double recombinants. So, smooth fruit and fine spines, yellow fruit are the double recombinants. The crossing over moves the middle allele over other alleles. Therefore, the gene order is f y s. The genes f and y are present in separate chromosomes.
c) The distance between f and y is,
= 100 x (67+46+3+4)/2000
= 6 cM
The distance between y and s is,
= 100 x (64+49+3+4)/2000
= 6 cM
Therefore, the gene map is,
6 cM. 6 cM
l-------------------l---------------------l
f. y s
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