Question by ionon: *10 POINTS* How could a farmer tell if his tomatoes are pure or hybrid?
In tomatoes, red fruit color is dominant, R, to yellow fruit color, r. A farmer has tomatoes that produce either red or yellow tomatoes. He has signed a contract with a large seed company to provide pure red, RR, and pure yellow seed, rr. They do not want any hybrids. How could the farmer tell if his red tomatoes are pure or hybrid?
Best answer:
Answer by Ben G
He could accomplish this by using a test-cross. By crossing a population with a test-cross, it enables you to determine if the genotypically unknown parent was homozygous or heterozygous. The test cross is always homozygouse recesssive.
For example,
AABB X aabb –> F1 generation 100% AaBb (the phenotype of the generation would be dominant in both traits).
AaBb X aabb –> F1 generation 3:1 phenotypic ratio (their would be a homozygous recessive genotype in the progeny which would stand out from the rest of the phenotypes–a clear marker to suggest that the parent in question was indeed heterozygous).
Hope this helps.
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He should perform a “testcross” by crossing the tomatoes in question with yellow-fruited plants.
If they are pure, all offpsring will be Red: RR x rr = all Rr
If they are hybrids (heterozygous), half the offspring will have yellow fruits: Rr x rr = 1:1 (red to yellow)
Do a test cross of the red with a double recessive yellow. If the red are homozygous then all the offspring will be red (RR x rr –>all Rr).
If the red are hybrids then the offspring will be 50:50 red:yellow (Rr x rr –>Rr &rr).