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小木虫论坛-学术科研互动平台 » 生物医药区 » 分子生物 » 存档旧帖 » 国外第一次上遗传课就被课后作业难倒，大家帮我看看，急！！
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yucheng9255

木虫 (著名写手)

[求助] 国外第一次上遗传课就被课后作业难倒，大家帮我看看，急！！

Graduate student Evert Explorer found an old ear of corn in Mexico that contained both plump kernels and shrunken kernels. Shrunken seed accounted for 25% of the total seed (a 3 to 1 segregation ratio).  Curious about the genetic cause of the shrunken seed, he brought the seed back to the UF, and planted these seeds as well as mutant seeds of three homozygous recessive mutants, termed shrunken-2, brittle-1 and brittle-2.  These mutants  are phenotypically indistinguishable from the mutant seed found in Mexico.
            Phenotypically mutant seed from Mexico did not germinate whereas non-mutant, or plump, seed from the ear did.  Six plants derived from the plump seed were crossed onto each of the three mutants.  Whereas all crosses onto plants from shrunken-2 and brittle-1 mutants yielded all plump seed, crosses of four of the six plants onto plants from the brittle-2 seeds gave rise to ears that were 50% plump and 50% shrunken.


What is the cause of the mutant seed found in Mexico?
Why didn’t all crosses onto brittle-2 yield mutant seed?
What is the origin of the 50:50 ratios in the brittle-2 crosses that segregated mutant seed?
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