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”. 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.

1. What is the phenotypic ratio of the progeny of that mating with the F1-plant?

2._______: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?

3._______: 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

1.

According to the given data, the mitochondrial genes are always inherited from only female parent.

Thus, the cross will be as follows:

Thus, the phenotypic ratio of offsprings that are obtained by crossing F1 with 3rd plant is 2:2, where 2 are fertile-pollen plants and 2 is sterile-pollen plant. This is because Rf is a dominant gene.

2.

Cross between F1 with 2nd plant is as follows:

The mitochondrial genotype is same for both the progeny because the mitochondrial genes are always inherited from only female parent.

3.

Cross between F1 with F1 is as follows:

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