(Problem 22a) Fine spines ( s ), smooth fruit ( tu ), and uniform fruit color (
ID: 93947 • Letter: #
Question
(Problem 22a) 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:
(Problem 22a) 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:
S U Tu 2 s u Tu 70 S u Tu 21 s u tu 4 S U tu 82 s U tu 21 s U Tu 13 S u tu 17 Total 230Explanation / Answer
Answer: Option D- Tu in middle, S-Tu = 21 m.u., U-Tu = 16 m.u.
S-Tu distance: S Tu and s tu are two recombinants.
RF = (2 + 4 + 21 + 21)/230
= 48/230
= 21% or 21 m.u.
U-Tu distance: u tu and U Tu are two recombinants.
RF = (2 + 4 + 13 + 17)/230
= 36/230
= 16% or 16 m.u.
Nonrecombinants = s u Tu and S U tu.
Double crossovers = s u tu and S U Tu.
Because Tu differs between the nonrecombinants and the double crossovers, Tu is the middle gene. So the answer is option D.
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