Given below are a few statements on concepts of molecular breeding.

• A. Correlations between quantitative traits can be because of pleiotropic effects of the same gene and/or genetic linkage of genes associated with the traits.
• B. In a Recombinant Inbred Line (RIL) population, genetic segregation of both dominant and codominant markers occurs in a 1:1 ratio.
• C. Near isogenic lines (NILs) can be produced by repeated backcrossing of the $F$ to a recurrent parent.
• D. SNPs are dominant markers.

Correct option is C

Statement A: Correct

Correlations between quantitative traits can arise due to:

1. Pleiotropy – when a single gene affects multiple traits.
2. Genetic linkage – when genes controlling different traits are located close to each other on the same chromosome, leading to their co-inheritance.

Statement B: Correct

Recombinant Inbred Lines (RILs) are developed by repeated selfing of hybrid generations, leading to homozygous lines. The expected genetic segregation ratio of codominant markers (like SSRs and SNPs) in RILs is 1:1. However, dominant markers do not segregate in a 1:1 ratio in RILs due to fixation of alleles through inbreeding.

Statement C: Correct

Near-Isogenic Lines (NILs) are developed through repeated backcrossing of an individual from an $$F_1$$​ population with a recurrent parent while selecting for a specific gene of interest. This process ensures that the NIL is genetically almost identical to the recurrent parent except for the introgressed gene of interest.

Statement D (Incorrect)

Single Nucleotide Polymorphisms (SNPs) are codominant markers, meaning they can distinguish between homozygous and heterozygous genotypes. Dominant markers, like RAPD and ISSR, only show the presence or absence of a band, whereas SNPs allow differentiation between alleles.

​Information Booster:

1. Pleiotropy vs. Genetic Linkage

   • Pleiotropy: One gene influences multiple traits.
   • Genetic Linkage: Two or more genes located closely on a chromosome are inherited together.

2. Recombinant Inbred Lines (RILs)

   • Developed by repeated selfing for several generations (usually F6F_6F6​ or more).
   • Used in Quantitative Trait Locus (QTL) mapping.

3. Near-Isogenic Lines (NILs)

   • Created by six or more backcrosses.
   • Used for fine mapping and functional validation of genes.

4. SNP Markers

   • Codominant markers used in genetic mapping.
   • Can differentiate between homozygous and heterozygous individuals.

5. Dominant vs. Codominant Markers

   • Dominant markers (e.g., RAPD, ISSR) only indicate presence/absence.
   • Codominant markers (e.g., SNPs, SSRs) distinguish between alleles.

6. Applications of Molecular Markers

   • Used in marker-assisted selection (MAS), plant breeding, and genetic diversity analysis.