Problem 6 - Campbell Biology

Question

In a species showing sporophytic incompatibility, which type(s) of pollen could successfully fertilize an \(S_{2} S_{3}\) flower? (A) \(S_{1}\) pollen from an \(S_{1} S_{3}\) flower (B) \(S_{2}\) or \(S_{3}\) pollen from an \(S_{2} S_{3}\) flower (C) \(S_{3}\) pollen from an \(S_{1} S_{1}\) flower (D) \(S_{1}\) pollen from an \(S_{1} S_{1}\) flower

Step-by-Step Solution

Answer

Pollens that can fertilize are (A) and (D).

Step 1: Understand Sporophytic Incompatibility

Sporophytic incompatibility is a mechanism in plants where the ability of pollen to fertilize a flower is determined by the interaction between the pollen's genotype and the stigma's genotype. If any of the alleles in the pollen match either of the alleles in the stigma, the pollen is rejected.

Step 2: Identify the Genotype of the Flower

The flower's genotype is given as \(S_{2} S_{3}\). This means the stigma will reject any pollen that contains \(S_{2}\) or \(S_{3}\) alleles.

Step 3: Analyze Each Pollen's Genotype

Evaluate each pollen type to see if it contains any alleles that would be rejected by the \(S_{2} S_{3}\) flower:(A) \(S_{1}\) pollen from an \(S_{1} S_{3}\) flower – Accepted (no matching alleles)(B) \(S_{2}\) or \(S_{3}\) pollen from an \(S_{2} S_{3}\) flower – Rejected (matching alleles)(C) \(S_{3}\) pollen from an \(S_{1} S_{1}\) flower – Rejected (matching allele)(D) \(S_{1}\) pollen from an \(S_{1} S_{1}\) flower – Accepted (no matching alleles)

Step 4: Conclusion

Based on the analysis, pollen types \(S_{1}\) from \(S_{1} S_{3}\) flower and \(S_{1}\) pollen from \(S_{1} S_{1}\) flower can fertilize an \(S_{2} S_{3}\) flower.

Key Concepts

Understanding Pollen-Stigma Interaction

Pollen-stigma interaction is a vital process in plant reproduction. When pollen lands on a stigma, a series of biochemical events occur. These interactions determine whether the pollen will be accepted or rejected by the stigma. In cases of sporophytic incompatibility, the stigma recognizes the genotype of the pollen. If the pollen shares any allele with the stigma, it is rejected.
This mechanism ensures genetic diversity and prevents inbreeding. For example, in a flower with an S2S3 genotype, any pollen carrying S2 or S3 alleles will be rejected. This is akin to a security check, where only pollen with different genotypes can pass through and proceed to fertilize the ovule.

Plant Reproductive Mechanisms

Plants have developed various reproductive mechanisms to ensure survival and adaptation. One such mechanism is genetic self-incompatibility, like sporophytic incompatibility. This system prevents self-fertilization and promotes cross-pollination.
Cross-pollination increases genetic variability, which is crucial for the adaptability and resilience of plant species. In sporophytic incompatibility, the pollen's outer layer (exine) determines compatibility. The exine's genotype, inherited from the father plant, must not match either allele of the stigma.
This type of reproductive barrier has evolved to maintain healthy populations by encouraging genetic diversity.

Genotype Compatibility

Genotype compatibility in plants is crucial for successful fertilization. Compatibility is assessed based on the genetic makeup of both the pollen and the stigma. In our example, an S2S3 flower will only accept pollen that does not carry S2 or S3 alleles.
The specific genotype of the pollen plays a crucial role. For instance, pollen from an S1S1 flower, which only carries the S1 allele, would be compatible with an S2S3 flower. This is because there is no sharing of alleles between the pollen and the stigma.
Understanding genotype compatibility helps breeders and botanists in controlling pollination and breeding strategies. It also provides insights into how plants avoid inbreeding and maintain genetic health.