In a unique species of plants, flowers may be either yellow, blue, red, or mauve
ID: 193692 • Letter: I
Question
In a unique species of plants, flowers may be either yellow, blue, red, or mauve. A pure-breeding line with blue flowers is crossed to a pure-breeding red-flowered line, and the resulting F1 plants have yellow flowers. In the F2 the following ratio is observed:
9/16 yellow: 3/16 blue: 3/16 red: 1/16 mauve
If pure-breeding yellow and mauve plants are crossed, the same F2 ratio is observed.
A. Give a concise genetic hypothesis for the inheritance of this trait (include number of genes, number of alleles and dominance relations between alleles).
B. Designate your own gene symbols and list the genotypes and ratios for each F2 class.
C. Determine the expected phenotypic ratios if the F1 from above is crossed to a pure-breeding mauve plant.
Explanation / Answer
Answer:
A).
Non epistatic Inter allelic genetic interaction:
In some cases two pairs of genes determine same phenotype but assorted independently, produce new phenotypes by mutual epistatic interaction. The F2 ratio remains the same as 9:3:3:1.
Gene A consists of two alleles A(dominant) & a (recessive)
Gene B consists of two alleles B(dominant) & b (recessive)
A_B_ = Yellow
A_bb = Blue
aaB_ = Red
aabb = Mauve
B).
Purple (AABB) x Mauve (aabb)
AaBb (Mauve) ---F1
F1 x F1
AB
Ab
aB
ab
AB
AABB (Yellow)
AABb(Yellow)
AaBB(Yellow)
AaBb(Yellow)
Ab
AABb(Yellow)
AAbb (blue)
AaBb(Yellow)
Aabb (blue)
aB
AaBB(Yellow)
AaBb(Yellow)
aaBB (red)
aaBb (red)
ab
AaBb(Yellow)
Aabb (blue)
aaBb (red)
aabb (Mauve)
Yellow : blue : Red : Mauve = 9 : 3 : 3 : 1
C).
AaBb (F1) x aabb—Test cross
Ab
AB
AaBb (yellow)
Ab
Aabb (blue)
aB
aaBb(red)
ab
aabb(mauve)
Purple : Blue : Red : Mauve = 1 : 1 : 1 : 1
AB
Ab
aB
ab
AB
AABB (Yellow)
AABb(Yellow)
AaBB(Yellow)
AaBb(Yellow)
Ab
AABb(Yellow)
AAbb (blue)
AaBb(Yellow)
Aabb (blue)
aB
AaBB(Yellow)
AaBb(Yellow)
aaBB (red)
aaBb (red)
ab
AaBb(Yellow)
Aabb (blue)
aaBb (red)
aabb (Mauve)
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