Question

Researchers investigating chromosome 9 of com, Zea mays, found four mutations. Interested in finding the relative locations of the four mutations, they bred two different triple mutant strains. One of the strains displayed phenotypes of male sterility (ms), white endosperm cap (wec), and brown midrib (brm). The other strain displayed the phenotypes of male sterility, white endosperm cap, and brittle stalk (bst). They crossed both mutant strains with a true breeding wild type strain to create two F, hybrids. They testcrossed each of the Fi hybrids and subsequently germinated and recorded the phenotypes 1000 seedlings of each cross. From the tables below, construct a linkage map for the four genes on chromosome 9 of com. Phenotype Count Phenotype Count All wild 298 173 All wild brm, mst, wec mst, wec, bst 308 brm, wec 155 bst 141 17 mst, wec 61 mst wec 74 brm, mst 110 brm 104 19 mst 101 mst, wec 70 67 bst, wec mst, bst wec

Answer 1

The greater number are showing that they are of parental type and the lowest number are showing that they are of double cross over type progenies.

During double cross over, it is found that middle gene is swapped between homologous chromosome.

Please look in the image for solution:

most wect/bstt wild learental most wee bst Hoouble crossover mstt wet b st Double cross over Imst wee bott Type- bst gene swapped. That's why bst gene I is in middle . Order is mst bst wec

Table 2 brmt mst tweet _ Parental brm mot wee troubte Gross Over bromt mott wie : Double cross blem mst wat Over type wee order is gene is in middle 0 brm wee mst

Now arrangements compare these two brm wec i mot - mot wec ost" . : : 13t h his! Itt brm wee bet mot That's why order of gene on chromosome 9 Lis.

Genetic distance blen met and bet Ujs = (single cross over ) + ( Double Crossover de tot Total mst but wed n met het wee (74) mot but wie met het weet 70 Genetic distance - 174+70 +19+175 10 0 L 1000 . - 18 CM Genetic distance blwn bot and wec mttbitt weet mot bst wect (10) - XT D mott bott wec'ttoy mst but wee Date: genetic distance 100 (110 +104) + ( 9+11 1000 25 cm Genetic distance blwn brm and wie is vormt west brott i brmt wer myt Hol) br to d º or, HerFM +(H)

Genetic distance - 111 7101 +6976 7 x100 pencerede 1000 534CM chromosome Map is AH brm wee bist 3425 mst K

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