1. 10pts In a three-point cross between a flowering plant heterozygous at the fo
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Question
1. 10pts In a three-point cross between a flowering plant heterozygous at the following loci LzlzGlglSusu and a homozygous recessive flowering plant (lzlzglglsusu) you obtain the gene combinations of the progeny frequencies below. You know the genes are all on the 3rd chromosome of the plants so there must be a fair amount of recombination taking place. Using these data, determine the gene in the middle, map the chromosomes in order and give distances between them.Phenotype of Testcross Genotype of Gametes Number of Progeny
Wildtype Lz Gl Su 286
Sugary Lz Gl su 4
Glossy, sugary Lz gl su 40
Lazy, glossy, sugary lz gl su 272
Lazy lz Gl Su 33
Lazy, sugary lz Gl su 44
Glossy Lz gl Su 59
Lazy, glossy lz gl Su 2
2. 3pts Now calculate the interference and coefficient of coincidence on the above data set and tell me what it means.
3.7pts Using the data from question 1 and the following information, can you fit these 4 genes into chromosome 3 of these flowering plants you have been studying: a) The chromosome is only 52 m.u. long, b) Gene Fr is flanking at one end, Gene K is on the opposite and gene Lz is directly in the middle, c) Gene K and Gl almost never have recombination events take place between them, d) Gene MM is 20 m.u. away from Su. E) Gene Bs is 10 m.u. away from MM and not far from Fr. Map the whole chromosome with all 7 genes.
Explanation / Answer
1). Given data is
Phenotype of Testcross Genotype of Gametes Number of Progeny
Wild type Lz Gl Su 286
Sugary Lz Gl su 4
Glossy, sugary Lz gl su 40
Lazy, glossy, sugary lz gl su 272
Lazy lz Gl Su 33
Lazy, sugary lz Gl su 44
Glossy Lz gl Su 59
Lazy, glossy lz gl Su 2
Total progeny = 740
Recombinant frequency between Lz and Gl = 40 + 33+ 44+ 59 = 176 / 740 = 0.24
Recombinant frequency between Gl and Su = 4 + 44+ 59+ 2 = 109 / 740 = 0.14
Recombinant frequency between Lz and Su = 4+ 40+ 33+ 2 = 79 / 740 = 0.10
From above frequencies the map distances are
Lz----------Su---------------Gl
ß--0.10--àß----0.14---à
ß--------0.24-------------à
2). coefficient of coincidence = actual double recombinant frequency / expected double recombinant frequency.
Actual double recombinant frequency = 44 + 59 = 103
Expected double recombinant frequency = 176 / 740 * 109 / 740 = 0.035 = 25.9 per 740.
coefficient of coincidence = 103 / 25.9
= 3.97
Interference = coefficient of coincidence – 1
= 3.97 – 1 = 2.97
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