Karyotypic evolution of ribosomal sites in buffalo subspecies and their crossbreed

Abstract

Domestic buffaloes are divided into two group based on cytogenetic characteristics and habitats: the “river buffaloes” with 2n = 50 and the “swamp buffaloes”, 2n = 48. Nevertheless, their hybrids are viable, fertile and identified by a 2n = 49. In order to have a better characterization of these different cytotypes of buffaloes, and considering that NOR-bearing chromosomes are involved in the rearrangements responsible for the karyotypic differences, we applied silver staining (Ag-NOR) and performed fluorescent in situ hybridization (FISH) experiments using 18S rDNA as probe. Metaphases were obtained through blood lymphocyte culture of 21 individuals, including river, swamp and hybrid cytotypes. Ag-NOR staining revealed active NORs on six chromosome pairs (3p, 4p, 6, 21, 23, 24) in the river buffaloes, whereas the swamp buffaloes presented only five NOR-bearing pairs (4p, 6, 20, 22, 23). The F1 cross-breed had 11 chromosomes with active NORs, indicating expression of both parental chromosomes. FISH analysis confirmed the numerical divergence identified with Ag-NOR. This result is explained by the loss of the NOR located on chromosome 4p in the river buffalo, which is involved in the tandem fusion with chromosome 9 in this subspecies. A comparison with the ancestral cattle karyotype suggests that the NOR found on the 3p of the river buffalo may have originated from a duplication of ribosomal genes, resulting in the formation of new NOR sites in this subspecies.

Genetic analysis of river, swamp and hybrid buffaloes of north‐east India throw new light on phylogeography of water buffalo (Bubalus bubalis)

“…; Degrandi et al . ). The two types differ in chromosome number: swamp buffaloes have 24 pairs, while river buffaloes have 25 pairs; the reduction of a pair of chromosomes in swamp buffalo is attributed to tandem fusion of chromosomes 4 and 9 in river buffalo (DiBerardino & Iannuzzi ).…”

“…They serve as one of the important sources of milk, draught, meat and hide. Broadly, there are two types of water buffalo viz., river (Bubalus bubalis bubalis) and swamp (Bubalus bubalis carabanesis) types (http://eol.org/pages/311907/overview), which are distinguished primarily based on their distinct morphology and karyotypes (Ianuzzi 2007;Michelizzi et al 2010;Degrandi et al 2014). The two types differ in chromosome number: swamp buffaloes have 24 pairs, while river buffaloes have 25 pairs; the reduction of a pair of chromosomes in swamp buffalo is attributed to tandem fusion of chromosomes 4 and 9 in river buffalo (DiBerardino & Iannuzzi 1981).…”

The distribution of 45S rDNA sites in bird chromosomes suggests multiple evolutionary histories

“…This fragility is probably originated by the repetitive nature of clusters or their intense gene expression activity (Huang et al, 2008). In the chromosome, these breakages may result in different types of rearrangements, such as translocation, fusions, duplications, and inversions, leading to rapid changes in the chromosomal distribution of the rDNA sites in closely related species (Datson and Murray, 2006;Degrandi et al, 2014).…”

Genome-wide analysis reveals genetic diversity, linkage disequilibrium, and selection for milk traits in Chinese buffalo breeds

“…To date, Chinese swamp buffaloes have been classed into 24 local types based mainly on the regional distribution [2]. To improve the milk and meat performance of swamp buffalo, crossbred buffalo by hybridizing the river-type bulls with swamp-type cows has been practiced in many Asian countries, and they are fertile, although the hybrid may have a lower reproductive value [3, 4]. The cross-breeding programs in China began in the 1950s by introducing the exotic river breeds such as Murrah and Nili-Ravi, which has resulted in the different crossbred breeds including the Murrah × local buffalo, Nili-Ravi × indigenous buffalo, and Murrah × Nili-Ravi × indigenous buffalo.…”