(B) You have developed a line of dwarf corn plants with purple leaves &salmon; s

Question

(B) You have developed a line of dwarf corn plants with purple leaves &salmon; silk. You cross a pure-bred line of plants with these traits with a true-breeding wild type corn. These hybrid plants are all normal heigl with purple leaves and salmon silk. You conduct a test cross using these hybrids, which results in the following progeny: 270 plants with purple leaves, yellow silk, and normal height 62 dwarf plants with purple leaves and salmon silk .4 plants with purple leaves, salmon silk, and normal height .235 dwarf plants with green leaves, salmon silk 60 plants with green leaves, yellow silk, and normal height 48 dwarf plants with purple leaves and yellow silk 7 dwarf plants with green leaves and yellow silk 40 plants with green leaves, salmon silk, and normal height i) Is the dwarf gene located on the same chromosome as the other genes? l) If so, determine the order of genes and calculate the map distance between the 3 genes ii) Consider why the map distances between the purple and salmon genes calculated in (A) and (B) are not identical

Explanation / Answer

Leaf colour purple P green p

silk variety yellow Y salmon y

plant height normal T dwarf t

PPYYTT= 270 (parental)

ppyytt= 235  (parental)

PPyytt= 62 (single recombinant between P and Y)

ppYYTT= 60 (single recombinant between P and Y)

PPYYtt=48 (single recombinant between T and Y)

ppyyTT=40 (single recombinant between T and Y)

ppYYtt=7 (Double recombinants)

PPyyTT=4 (double recombinant)

1. Yes dwarf gene is located on same chromosome beacuse recombination frequency is less than 50%

Recombination frequency of height gene= (48+40+7+4)/726*100= 13.6%

2. If we look at the parental and double cross over genotypes we see that silk colour gene is flipped it means silk colour is in middle

map distance between P and Y= (60+62+7+4)/726*100= 18.3% or 18.3cM

Map distance between Y and T = (48+40+7+4)/726*100=13.6% or 13.6 cM

so gene order is P------Y--------T

3. purple and salmon are on different chromosme

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