ABSTRACTS
Genetic diversity and genetic distance of five populations of the Nigerian breeds of goat were investigated using random amplified polymorphic DNA markers. Five breeds of goat were used for the study and each breed constituted a population, hence, the five populations considered in the study. The populations were: Sokoto Red (SR), Sahel (SH), Kano Brown (KB), Bornu White (BW) and West African Dwarf (WAD) goats. The experiment was conducted within four geographical zones of Nigeria: South east, North west, North east and North central. One hundred and twenty (120) blood samples were randomly collected from various locations across the four geographical zones in Nigeria. The samples were collected from the stocks at the central markets, which served as collection point from all the localities and from household goat keepers. Varying numbers of sample sizes (Sokoto Red = 23, Kano Brown = 21, Bornu White = 23, WAD = 26 and Sahel = 27) were collected from each breed. The blood samples were collected from the jugular vein of the animals through a process known as venipuncture. Approximately, 5 ml of blood was collected aseptically from each animal into an EDTA container, using 23 gauge sterile needle and syringe, and was stored at -20oC using (ethylene-di-amine-tetra-acetic acid, EDTA) as anticoagulant containers. The DNA samples were isolated and purified from the 120 blood samples following protocol as recommended by (ZYMO RESEARCH CORPORATION, e-mail: info@zymoresearch.com). The RAPD-PCR reaction followed the procedure described by El Hentati et al., (2012). Seven random primers were used for this study but only three (3) primers produced clearly polymorphic and reproducible bands whereas four (4) failed to produce any band. Allele frequency per population per loci under consideration exceeded the minimum allele frequency (MAF) limit 10%. Level of polymorphism per primer varied from 43 – 80%. Total of 20 scoreable bands were obtained and thirteen (13) out of which were polymorphic to arrive at a total of 65% polymorphism. Genetic diversity of the studied populations was measured with three indices: (Nei’s genetic diversity, Shannon’s information index, Observed and Effective number of alleles). Observed number of allele (Na) was 2.0000 across the populations while Effective number of alleles (Ne) varied from 1.9003 in WAD to 1.9900 in Sahel population. However, SR, KB and BW had Ne values of 1.9897, 1.9287 and 1.9836 respectively. Nei’s heterozygosity varied across the populations with highest values 0.4975 and 0.4974 obtained in Sahel and Kano Brown respectively whereas lowest value 0.4736 was obtained in WAD. Shannon’s Information index followed similar trend across with average of 0.6822. The mean of coefficient of gene differentiation Gst was (0.0139) and mean of gene flow Nm across populations was (35.3710). The highest genetic similarity (0.9995) and lowest genetic distance (0.0005) was recorded between Sokoto Red and Sahel, while the lowest similarity (0.9505) and highest genetic distance (0.0507) was recorded between Bornu White and WAD. Populations with higher similarity indicated that they are of closer descent and closer geographical locations. The unweighted pair group method of arithmetic means (UPGMA) dendrogram based on Nei’s genetic distance clearly separated the five populations into two clusters. The closest relationship was observed between Sokoto Red, Sahel and Bornu White goat populations/breeds and the farthest relationship was observed between WAD and Sokoto Red populations. It was concluded that the high similarity obtained in this study was as a result of loss of heterozygosis in the populatons of Nigerian breeds of goat which may have originated among mates in each population/breed. However, the results of this experiment can offer some crucial scientific data useful for breeding programme of Nigerian breeds of goats.
CHAPTER ONE
1.0. INTRODUCTION
Nigeria is a country with heavy human population of about 168.8 million (U.S.C.B., 2012), and this population is continuously on the increase. The increase has led to the high demand for the available animal and animal products in all parts of the country, to meet up with the minimum animal protein requirement per individual per day. The protein intake of an average Nigeria is 45.5g per head per day as against the Food and Agricultural Organization’s recommended minimum intake of 70g per head per day, of which 35g should be of animal source (FAOSTAT, 2010). The inadequate supply of animal protein in Nigeria can be attributed to inadequate production potentials of the most common sources of meat which include poultry, goat, cattle, pig, sheep, rabbit etc. Gambo et al. (2004) reported that among the cheapest and mostly affordable protein source for this ever increasing population is mainly the poultry products and chevrons (goat meat).
Goat (Capra hircus) is one of the smallest domesticated ruminants which are managed for the production of milk, meat, wool and leather particularly in arid, semi-tropical or mountainous countries (Morand-Fehr, 2004). Goat is the most prolific ruminant among all domesticated ruminant under tropical and subtropical conditions. It is a resourceful and efficient ruminant producing meat, milk, skin and hair (Morand-Fehr, 2004).
Goats constitute the largest group of small ruminant livestock in Nigeria totalling about 53.8 million and also constituting 6.2 percent of the World’s goat population (FAOSTAT, 2011). Surveys have shown that up to 85 percent of rural households, poor farmers and small-time business people of all age groups and sexes keep goat (FDLPCS, 2007). The ability of goats to tolerate harsh climates, the presence of trypanotolerance in some breeds (Salako, 2004), suitability to traditional systems on account of small size, short generation interval (Abdul-Aziz, 2010) and ability to thrive on poor quality diets provided by scarce grazing on marginal lands (Adedeji et al., 2011) all combine to make small ruminants strategic to increasing livestock productivity in rural agricultural systems (Adedeji et al., 2011). Despite these advantages, little attention has been paid to the genetic characterization and possible improvement of small ruminants in Nigeria.
Detailed knowledge of population structures among and within breeds of livestock is essential for establishing conservation priorities and strategies (Caballero and Toro, 2002). Livestock production is vital to subsistence and economic development (Yakubu and Ibrahim, 2011). The ever increasing demand for livestock production to cater for the
Molecular markers are important tools in tagging desirable loci underlying the expression of traits which have breeding importance. Estimations of genetic variation increasingly are being based upon information at the DNA level by various molecular markers such as, Randomly amplified Polymorphic DNA (RAPD), Amplified Fragment Length Polymorphism (AFLP), Restriction Fragment Length Polymorphism (RFLP) (Rincon et al., 2000), Simple Sequence Repeat (SSR) or Microsatellite (Dalvit et al., 2008) etc. Among them, RAPD markers, generated by the polymerase chain reaction (PCR) is widely used since the 1990's to assess infra-specific genetic variation at nuclear level (Welsh and McClelland, 1990; Williams et al., 1990).
In recent years, a range of innovations in molecular genetics have been developed for the study of genetic variation and evolution of populations using DNA marker genotype information. The study of genetic variation plays an important role in developing rational breeding strategies for economical animal species (Maudet et al., 2002). Genetic analysis of livestock species have been performed using of polymorphic markers such as restriction fragment length polymorphisms (RFLPs) and microsatellites (Rincon et al., 2000; Dalvit et al., 2008). However, their use is limited since designation of these genetic markers is expensive, technically demanding and is time consuming (Beuzen et al., 2000). However, Random amplified polymorphic DNA (RAPD) assay which uses short oligonucleotide primers of arbitrary sequence to amplify genomic DNA by Polymerase Chain Reaction (PCR) enables an approach for identifying polymorphic and genetic markers faster (Cushwa and Medrano, 1996). A primer is a strand of nucleic acid that serves as a starting point for DNA synthesis. They are required for DNA replication because the enzymes that catalyze the process, DNA polymerase, can only add new nucleotides to an existing strand of DNA. These markers have been used for genotype identification (Tinker et al., 1993), construction of genetic maps (Maddox and Cockett, 2007), etc. The RAPD technique has also been used in analysis of genetic variations between different breeds of animals such as fish (Ambak et al., 2006), chicken (Okomus and Kaya, 2005), cattle (Hassen et al., 2007), buffaloes (Abdel-Rahman and Elsayed, 2007), goat (Yadav and Yadav, 2007) and sheep (Kunene et al., 2009).....
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