Molecular breeding is the application of molecular biology tools, often in plant breeding.
The areas of molecular breeding include:
QTL mapping or gene discovery
Marker assisted selection and genomic selection
Genetic engineering
Genetic transformation
Genotyping and creating molecular maps - genomics
The commonly used markers include Simple sequence repeats (or microsatellites), single nucleotide polymorphisms (SNP). The process of identification of plant genotypes is known as genotyping.
Development of SNPs has revolutionized the molecular breeding process as it helps to create dense markers. Another area that is developing is genotyping by sequencing.
Phenotyping - phenomics
To identify genes associated with traits, it is important to measure the trait value - known as phenotype. "omics" for measurement of phenotypes is called phenomics. The phenotype can be indicative of the measurement of the trait itself or an indirectly related or correlated trait.
QTL mapping or association mapping
Genes (Quantitative trait loci (abbreviated as QTL) or quantitative trait genes or minor genes or major genes) involved in controlling trait of interest is identified. The process is known as mapping. Mapping of such genes can be done using molecular markers. QTL mapping can involve single large family, unrelated individuals or multiple families (see: Family based QTL mapping). The basic idea is to identify genes or markers associated with genes that correlate to a phenotypic measurement and that can be used in marker assisted breeding / selection
Marker assisted selection or genetic selection
Once genes or markers are identified, they can be used for genotyping and selection decisions can be made.
Marker-assisted backcrossing (MABC)
Backcross is crossing F1 with its parents to transfer a limited number of loci (e.g. transgene, disease resistance loci, etc.) from one genetic background to another. Usually the recipient of such genes is good adapted cultivars otherwise except the gene that is to be transferred. So we want to keep genetic background of the recipient genotypes, which is done by 4-6 rounds of repeated backcrosses while selecting for the gene of interest. We can use markers from the whole genome to recover the genome quickly in 2-3 rounds of backcrossing might be good enough in such situation.
Marker-assisted recurrent selection (MARS)
MARS include identification and selection of several genomic regions (up to 20 or even more) for complex traits within a single population.
Genomic selection
Genomic selection is novel approach to traditional marker-assisted selection where selection are made based on few markers. Rather than seeking to identify individual loci significantly associated with a trait, genomics uses all marker data as predictors of performance and consequently delivers more accurate predictions. Selection can be based on genomic selection predictions, potentially leading to more rapid and lower cost gains from breeding.Genomic prediction combines marker data with phenotypic and pedigree data (when available) in an attempt to increase the accuracy of the prediction of breeding and genotypic values.
Transfer of genes make it possible for horizontal transfer of genes from one organism to another. Thus plants can receive genes from humans or algae or any other organism. This provides limitless opportunity in breeding crop plants.
