Plant breeders have long appreciated the phenomenoncalled hybrid vigor or heterosis, in which hybridsformed between two inbred strains have increasedvigor and crop yield relative to the two parental strains.Starting in the 1930s, seed companies exploited the cytoplasmic male sterility (CMS) phenomenon in cornthat was described in Problem 17 so that they couldcheaply produce hybrid corn seed to sell to farmers.This type of CMS is caused by mutant mitochondrialgenomes that prevent pollen formation.a. How would CMS aid seed companies in producinghybrid corn seed?Dominant Rf alleles of a nuclear gene called Restorersuppress the CMS phenotype, so that Rf-containingplants with mutant mitochondrial genomes are malefertile.b. Describe a cross generating hybrid corn seed thatwould grow into fertile (self-fertilizing) plants.(Farmers planting hybrid seed want fertile plantsbecause corn kernels result from fertilized ovules.)c. One of the historical challenges in the commercialization of hybrid corn produced through CMS wasthe maintenance of strains with CMS mitochondria: How could the seed companies keep producing male sterile corn plants if these plants neverthemselves produced pollen? Suggest a strategy bywhich the seed companies could continue to obtainmale sterile plants every breeding season.d. Are there any potential disadvantages to the use ofhybrid corn? If so, what issues might arise?
Plant breeders have long appreciated the phenomenon
called hybrid vigor or heterosis, in which hybrids
formed between two inbred strains have increased
vigor and crop yield relative to the two parental strains.
Starting in the 1930s, seed companies exploited the cytoplasmic male sterility (CMS) phenomenon in corn
that was described in Problem 17 so that they could
cheaply produce hybrid corn seed to sell to farmers.
This type of CMS is caused by mutant mitochondrial
genomes that prevent pollen formation.
a. How would CMS aid seed companies in producing
hybrid corn seed?
Dominant Rf alleles of a nuclear gene called Restorer
suppress the CMS
plants with mutant mitochondrial genomes are male
fertile.
b. Describe a cross generating hybrid corn seed that
would grow into fertile (self-fertilizing) plants.
(Farmers planting hybrid seed want fertile plants
because corn kernels result from fertilized ovules.)
c. One of the historical challenges in the commercialization of hybrid corn produced through CMS was
the maintenance of strains with CMS mitochondria: How could the seed companies keep producing male sterile corn plants if these plants never
themselves produced pollen? Suggest a strategy by
which the seed companies could continue to obtain
male sterile plants every breeding season.
d. Are there any potential disadvantages to the use of
hybrid corn? If so, what issues might arise?
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