Homozygousity-assessment for B blood-group alleles in a layer population undergoing recurrent inbreeding by PCR based simple sequence repeat polymorphism

Suryakant Mishra, R.P. Sharma and S.R. Sharma
Project Directorate on Poultry, Rajendranagar, Hyderabad - 500 030

A brown egger population maintained at the PD on poultry, under deliberate inbreeding conditions for 3 consecutive generations was subjected to homozygousity-assessment for the “B” Blood-group alleles. The B-alleles are the constituents of the Major histocompatibility complex (MHC) which are usually defined by the serological reactions concerning the B-F (class-I) and B-G (class-IV) antigens expressed in the chicken erythrocytes against the corresponding antibodies (allo-antisera). An attempt was made in this study to examine the variant B-alleles segregating in these inbred chickens [2 distinct groups representing recurrent full-sib (FS) and half-sib (HS) matings respectively] versus a non- inbred random-mated group of chickens, using a SSRP marker (LEI-0258- reference International Consensus Gene-map). The LEI-0258 is a simple sequence repeat (SSR) locus that is physically located within the MHC (chromosome-16) spaced between the BF & BG regions. This SSR was used as the handle to type the MHC variants harbored by these 3 groups. Standard PCR conditions specific to the LEI-0258 was followed and the PCR-products were resolved in a 3% agarose-gel matrix. The results realized from the gel-documented allele types showed that: heterozygousity existed at the rate of ≥ 0.50, for all the non-inbred samples, while it was drastically low for both the FS and HS groups (0.1 to 0.2) concerning all the existent allele types. This also meant that the predominating B-alleles present in these inbred subpopulations were slowly attaining the homozygous states (varying from 80% to 90% across the H.S and F.S groups). When compared against the MHC haplotype reference available for 7 B-alleles (B2, B5, B12, B13, B15, B19 and B21) [source: B-congenic groups of avian diseases and oncology lab, MI-48823, USA], it was noticed that most of the B-alleles in these sub populations did not match with 6 of these B reference-types. However, a couple of the FS-families were heterozygotic for the B-21 types (carrying one 357bp allele). The study concluded that deliberate inbreeding for 3generations brought in the homozygousity at the B-locus proportionate to the expected-rise in inbreeding co-efficient as compared to the random mating situation. Further, this layer population possessed many other B-allele variants as detected vide this SSR locus, which could be useful in developing newer B-congenic sub-populations / strains from these populations for further studies.

Source : IPSACON-2005

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