In some plant species, pollen development is influenced by genes in the nuclear

Question

In some plant species, pollen development is influenced by genes in the nuclear genome and by genes in the mitochondrial genome. In most species, the mitochondria (and chloroplasts) are only inherited through the female gametes (i.e., a type of maternal or extranuclear inheritance). The genotype of the pollen-sterile mitochondria is symbolized as “mtS” (same as “CMS” in the text, p388-89). The genotype of pollen-fertile mitochondria is symbolized “mtF”. The mitochondrial genome of a plant, the entire plant, is either mtS or mtF. Plants with mtF have a pollen-fertile phenotype regardless of the genotype of the nuclear genome . Plants with mtS may be either pollen-fertile or pollen-sterile, depending on the alleles in the nuclear genome. Some strains of corn have a dominant nuclear gene, Rf, that restores pollen fertility in plants that have the mtS. Plants that have the Rf allele are pollen-fertile regardless of the genotype of the mitochondrial genome. Rf is completely dominant to allele rf (ie., rf is the recessive allele that fails to restore pollen fertility in plants that have the mtS).

A pollen-sterile plant (plant 1, the female, genotype mtS rf rf) is mated with plant 2, (the male, genotype mtF RfRf), to produce F1 generation plants. The F1 plants are used as females in a mating with plant 3, genotype mtF rfrf.

_______: What is the phenotypic ratio of the progeny of that mating with the F1-plant?

_______:The F1 plants are used as the male in a mating with plant 2. What is the ratio of mitochondrial genotypes in the progeny of that mating?

_______: The F1 plants were mated with themselves (ie., a self-pollination) and produced 800 progeny. How many progeny are expected to be pollen-sterile?   Show your work.

Explanation / Answer

The phenotypic ratio of the progeny will be all pollen - fertile , It should have been 2:2. pollen fertile and pollen sterile since Rf homozygous is mated it will revert mtS to mtF hence the ration will be 1:1:1:1

F1 X plant 2 - All pollen fertile offspring mts Rf rf X mtF Rf Rf = mtS Rf Rf, mtsRf rf, mtF Rf rf and mtF Rf Rf

F1 X F1 - 3:1 of pollen-fertile and pollen sterile. mtS Rf rf X mtS Rf - mtS Rf Rf, mtsRf rf, mts rf rf mts Rf Rf

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