6. In certain plant species such as tomatoes and petunias, a highly polymorphic incompatibility gene Swith more than 100 known alleles prevents self-fertilization and promotes outbreeding. In this form ofincompatibility, a plant cannot accept sperm carrying an allele identical to either of its own incompatibility alleles. If, for example, pollen carryingsperm with allele S1of the incompatibility genelands onto the stigma (a female organ) of a plantthat also carries the S1allele, the sperm cannot fertilize any eggs in that plant. (This phenomenonoccurs because the pollen grain on the stigma cannotgrow a pollen tube to allow the sperm to unite withthe egg.)For the following crosses, indicate whether anyprogeny would be produced, and if so, list all possiblegenotypes of these progeny. a. ♂ S1S2× ♀ S1S2b. ♂ S1S2× ♀ S2S3c. ♂ S1S2× ♀ S3S4d. Explain how this mechanism of incompatibilitywould prevent plant self-fertilization.
6. In certain plant species such as tomatoes and petunias, a highly polymorphic incompatibility gene S
with more than 100 known alleles prevents self-fertilization and promotes outbreeding. In this form of
incompatibility, a plant cannot accept sperm carrying an allele identical to either of its own incompatibility alleles. If, for example, pollen carrying
sperm with allele S1
of the incompatibility gene
lands onto the stigma (a female organ) of a plant
that also carries the S1
allele, the sperm cannot fertilize any eggs in that plant. (This phenomenon
occurs because the pollen grain on the stigma cannot
grow a pollen tube to allow the sperm to unite with
the egg.)
For the following crosses, indicate whether any
progeny would be produced, and if so, list all possible
genotypes of these progeny.
a. ♂ S1
S2
× ♀ S1
S2
b. ♂ S1
S2
× ♀ S2
S3
c. ♂ S1
S2
× ♀ S3
S4
d. Explain how this mechanism of incompatibility
would prevent plant self-fertilization.
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