Plant molecular markers and self-incompatibility: A cDNA clone prepared from stigma mRNA of Brassica oleracea is used as a probe on DNA digests of segregating populations to recognize which genetic elements?

Introduction / Context:
Brassica species such as Brassica oleracea (cabbage, cauliflower, broccoli) exhibit a sporophytic self-incompatibility system controlled at the S-locus. Stigmatic mRNAs include transcripts from S-locus receptor kinase and related genes. A cDNA probe derived from stigma mRNA can track allelic variation in segregating populations, aiding marker-assisted selection and genetic studies of self-incompatibility.

Given Data / Assumptions:

• cDNA clone is prepared from stigma mRNA of Brassica oleracea.
• Probe is hybridized to DNA digests (e.g., Southern blots) from a segregating population.
• Goal is to identify polymorphisms linked to a trait expressed in stigmas.

Concept / Approach:
The key transcripts in Brassica stigmas related to self-incompatibility map to the S-locus. Using a stigma-derived cDNA probe, one can detect restriction fragment length polymorphisms that cosegregate with S-alleles. This enables assignment of specific S-haplotypes in breeding material or mapping populations without phenotyping every cross.

Step-by-Step Solution:

Verification / Alternative check:
Classical Brassica genetics shows tight linkage between stigma-expressed S-locus genes and SI phenotype; cosegregation of hybridization patterns with SI classes validates allele identification in progenies.

Why Other Options Are Wrong:

• Aegilops or Triticum: different genera (wheat relatives), unrelated to Brassica S-locus diagnostics.
• Both (a) and (b): mixing unrelated cereals and Brassica is incorrect.
• Only R genes: stigma cDNA probes target SI genes rather than general disease resistance loci.

Common Pitfalls:
Confusing sporophytic SI in Brassica with gametophytic SI systems of other plants; the molecular markers and expressed genes differ between systems.

Final Answer:
S alleles (self-incompatibility alleles)