Briefly describe the procedure for genomic selection and compare it with marker-assisted selection.

Genomic selection (GS) and marker-assisted selection (MAS) are both molecular breeding approaches that utilize genetic information to enhance the efficiency and accuracy of trait selection in plant breeding. However, they differ in their methodologies and objectives. Here's a brief description of the procedures for each approach and a comparison between them:

Marker-Assisted Selection (MAS):

 

MAS involves the use of molecular markers linked to target genes or genomic regions associated with desired traits.

The procedure typically includes the following steps:

·         Marker Development: Molecular markers are identified and developed based on their association with target traits through techniques such as genetic mapping or association studies.

·         Genotyping: Individuals in the breeding population are genotyped using the developed markers to determine the presence or absence of target alleles.

·         Selection: Breeders select individuals with the desired marker alleles for further breeding based on the marker-trait associations.

·         MAS allows for the direct selection of individuals carrying specific alleles associated with target traits, leading to more efficient trait improvement compared to traditional phenotypic selection.

Genomic Selection (GS):

GS involves the use of genome-wide molecular markers distributed across the entire genome to predict the breeding value of individuals for complex traits.

The procedure typically includes the following steps:

·         Training Population: A training population consisting of individuals with both marker data and phenotypic data is used to establish the relationship between marker genotypes and phenotypic traits.

·         Marker Effects Estimation: Statistical models, such as genomic prediction models, are used to estimate marker effects based on the training population data.

·         Genomic Prediction: Marker effects estimated from the training population are used to predict the breeding value of individuals in the selection population using marker genotypes alone.

·         Selection: Individuals with the highest predicted breeding values are selected for further breeding, regardless of their phenotypic performance.

GS aims to capture the additive genetic variance distributed across the entire genome to predict the breeding value of individuals more accurately, especially for complex traits with low heritability or controlled by multiple genes.

Comparison:

Scope of Selection:

·         MAS: Targets specific genes or genomic regions associated with known traits.

·         GS: Considers genome-wide marker information to predict breeding values for multiple traits simultaneously, including those controlled by unknown genes.

Prediction Accuracy:

·         MAS: Prediction accuracy depends on the strength of the marker-trait association and the heritability of the trait.

·         GS: Generally provides higher prediction accuracy, particularly for complex traits with low heritability or controlled by multiple genes.

Genetic Gain:

·         MAS: Facilitates the selection of individuals with known favorable alleles, leading to rapid genetic gain for targeted traits.

·         GS: Allows for the selection of individuals with high predicted breeding values, resulting in more efficient genetic gain across multiple traits simultaneously.

Resource Requirements:

·         MAS: Requires marker development and genotyping, which can be resource-intensive.

·         GS: Requires a well-characterized training population for model training, but once established, marker genotyping costs are relatively lower for selection.

In summary, MAS and GS are both valuable tools in plant breeding, each with its advantages and limitations. While MAS enables targeted selection based on known genetic information, GS offers broader genomic predictions for complex traits, allowing for more comprehensive and accurate trait improvement in breeding programs.