– Chromosomal Patterns and Variability in the African Giant Rat –
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ABSTRACT
The studies of mammalian chromosomes have constituted an effective area of investigation to explain their relationship.
The entire chromosome set of a species is known as a karyotype. Many rodent species show a tendency for extensive chromosomal variability within species and species complexes.
The use of molecular methods to provide more insight into the taxonomy and phylogeny of Cricetomys was recommended.
Karyotypic studies were carried out on the African Giant rat, (Cricetomys gambianus, Waterhouse-1840) with the aim of determining its chromosome number, length, centromeric indices and nomenclature.
The chromosomes were prepared from the conventional bone marrow of 10 African Giant rats – five male and five female Giant rats, treated intraperitoneally with 2 ml of 0.04% colchicines for 3 hours.
Chromosomes in well-spread cells were counted and measured using KaryoType computer software. Arm lengths, centromeric indices and nomenclature were determined from these measurements and were expressed in micrometre (µm).
TABLE OF CONTENTS
Cover page ………………..i
Fly leaf………………ii
Title page……….iii
DECLARATION……………..iv
CERTIFICATION…………….v
ACKNOWLEDGEMENTS ……………vi
TABLE OF CONTENTS ………………vii
LIST OF TABLES ……………….x
LIST OF FIGURES ………….xii
LIST OF PLATES ………………xiv
LIST OF ABBREVIATIONS ………….xv
ABSTRACT…………….xvii
1.0 INTRODUCTION………………..1
1.1 Background ……………..1
1.2 Statement of Research Problem ……………..9
1.3 Justification of the Study………………9
1.4 Aim and Objectives of the Study ………..10
1.4.1 Aim of the study……………….10
1.4.2 Objectives of the study…………….10
1.5 Research Hypothesis…………………10
2.0 LITERATURE REVIEW …………..11
2.1 Karyogenetics of the African Giant Rat ………….11
3.0 MATERIALS AND METHODS ………25
3.1 Materials………………..25
3.1.1 Acquisition of the experimental animals ………………25
3.1.2 Equipment………………25
3.2 Methodology ………………….26
3.2.1 Injection and sacrifice of the animals ………….26
3.2.3 Place where karyotype studies were carried out…………..27
3.2.4 Extraction of cells…………………27
3.2.5 Fixation of cells………………….27
3.2.6 Spreading of cells and air drying …………….30
3.2.7 Preparation of Giemsa Stain ………..30
3.2.8 Staining of cells……………..30
3.2.9 Chromosome analysis…………..33
3.3 Components of karyotypic patterns of Cricetomys gambianus…………34
3.4. Statistical Analyses……………..36
4.0 RESULTS ……………37
4.1 Anthropometric measurements of Cricetomys gambianus……………………………….37
4.1.1 The mean weight and length of Cricetomys gambianus…………………………………….37
4.2 Chromosomal Numbers, Lengths and Morphology of Cricetomys gambianus….41
4.2.1 The mean chromosomal arm lengths of Cricetomys gambianus…………………………67
4.2.2 Sexual dimorphism of chromosomal arm lengths of Cricetomys gambianus ……….69
4.2.3 Sexual dimorphism of the total chromosomal lengths of Cricetomys gambianus….71
4.2.5 Sexual dimorphism of the centromeric indices of Cricetomys gambianus……………73
4.2.7 Chromosomal nomenclature of Cricetomys gambianus…………………………………….75
5.0 DISCUSSION………77
6.0 CONCLUSION AND RECOMMENDATION …………..85
6.1 Conclusion ………………85
6.2 Recommendations……………..85
6.3 Contributions to Knowledge ………..87
REFERENCES………..88
INTRODUCTION
The African Giant rat (AGR) also known as Gambian pouched rat belongs to the order Rodentia, Suborder Myomorpha, family Cricetidae, subfamily Cricetomyiane and genus Cricetomys (Delany and Happold, 1979). It is a wild rodent consumed by the rural population in Nigeria.
Two species have been recorded in Nigeria, Cricetomys emni and Cricetomys gambianus, Waterhouse-1840 (Happold, 1987).
Other Gambian species exist in South Africa and they include Cricetomys gambianus adventor, C. gambianus selindensis and C. gambianus cunator.
Cricetomys emni is distributed naturally in the rain forest zone and is not associated with human habitation. It is less common than the Gambian Giant rat (Happold, 1987).
African giant pouched rat is found throughout tropical and subtropical Africa, South of the Sahara Desert down to about 27o South latitude (Novak, 2009).
Their native range stretches from the Atlantic Ocean coast of West Africa, east across the Congo Basin to the Indian Ocean Coast of East Africa (Peterson et al., 2006) and southwards into the Transvaal and KwaZulu-Natal Provinces of South Africa (Malekani et al., 2002).
REFERENCES
Abraham, Z. and Prasad, P. N. (1983). A system of chromosome classification and nomenclature, Cytologia, 48: 95-101.
Adegoke, J. A. and Ejere, V. C. (1991). Despcription of the chromosomes of three lizard species belonging to the genus Mabuya (Scincidae, Reptilia). Caryologia, 44 (3), 333-342.
Aguilar, G. H. (1993). The karyotype and taxonomic status of Cryptomys hottentotus darlingi (Rodentia: Bathyergidae). South African Journal of Zoology, 28: 201-204.
Ajayi, S.S. (1975). Observations on the biology, domestication and reproductive performance of the African giant rat (Cricetomys gambianus, Waterhouse) in Nigeria. Mammalia, 39: 343-364.
Ajayi, S.S. (1977). Field observations on the African giant rat, Cricetomys gambianus Waterhouse in Southern Nigeria. East African Wildlife Journal, 15: 191-198.
Akintoye, M.A. and Awopetu, J.I. (2005). Chromosomal studies of the African giant rat and the hairy soled gerbils (Rodentia, Cricetidae). Ife Journal of Science, 7: 163-171.
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