1.0                                                       INTRODUCTION


Genetics is the science of heredity. It is concerned with the behaviour of particulate ‘factor ‘ now called genes, which are passed from parent to their offspring in the reproductive process. genes are responsible for differences and similarities of various characters or traits among individuals. The term genetics was first suggested in 1906 by an experimental geneticist, William   bateson. Among its different areas are mendelian molecular, quantitative and population genetics.

            Mendelian genetics deals with simply inherited traits, that is, those governed by relatively few gene pair differences   and whose transmission follows simple mendelian rules. These characters are also referred to as mendelian characters.

Most molecular traits, such as restriction fragment length polymorphism (RFLPS) are also inherited in a mendelian fashion. Like classical genetics, molecular nature and largely concerned with nature and transmission of genetics

Information and with the method of translation of this information into observable characters. Quantitative genetics on the other hand, is concerned with inheritance of quantitative characters. Unlike mendelian traits, these characters  are governed by few or several genes of small effect, which cannot be individually  identified by their segregation. Consequently, the methods of quantitative genetics are different from those of mendelian genetics. However, the genes governing quantitative characters obey the same laws of transmission as those governing quantitataive (mendelian ) characters . this  means that quantitative genetics founded on menelian principles.



 There can be little doubt that the first human on earth pondered the observation that children resembled their parents more  than other member of population, unfortunately, however, we havee no record of their ideas as to why this occurred. The Greek philosophers, Hippocrates and Aristotle obviously taught extensively about this fact and developed theories to explain resemblances among relatives.

            Gregor mendel (1822-1884) is appropriately called the father of genetics. His precedent –setting experiments with garden peas pisum sativum  published in 1866, were conducted in the limited space of a monastery garden while he was also employed as a substitute school teacher. The conclusion he drew from his elegant investigations constitute the foundation of today’s science of genetics. mendels was not the first to perform hybridization experiment, but he was one of the first to consider the result in terms of single traits. Sagret in 1826 had studied the inheritance of contracting traits. Other of Mendel’s predecessors had considered whole organisms which incorporate a nebulous  complex of traits, thus they could observed only that similarities and differences occurred among parents and progeny, and so missed the significance of individual differences. Employing the scientific method, Mendel designed the necessary experiments, counted and classified the peas resulting from his crosses, compared the proportion with mathematical models, and formulated a hypothesis for these differences. In 1900, mendel’s paper was discovered simultaneously by three botanists; Hugo devries in Holland, known for his mutation theory and studies on the evening primrose and maize, Carl correns in Germany, who investigated maize, peas, and beans, and Eric von tschermak seysenegg in Austria, who worked with  several plants including garden peas. Each of these investigators obtained evidence for mendel’s principle from his own independent studies. They all found Mendel ‘s report while searching the literature for related work and cited it in their own publications. william bateson, an English man, gave this developing science the name ‘genetics‘ in 1905. he coined the term from a greek word meaning “ to generate”.

            In addition to naming the science, Bateson actively promoted Mendel’s  view of paired genes. he used the word ’’allelomorph”, subsequently shortened to “allele”, to identity members of pairs that control different alternative traits. Also during the early 1900s, a French man, Lucien cuenot, showed that genes controlled fur colour in the mouse; an American, W.E castle, related genes to sex and to fur color  and pattern in mammals, and a Dane W.L Johannsen , studied the influence of heredity and environment in plants. Johannson began using the word “gene” from the last syllable of Darwin’s term ‘’pangene”   the gene concept, however, had been implicit in mendel’s visualization of a physical element or factor (Anlgae ) that acts as the foundation for development of a trait. These men and their peers were able to build on the basic principles of cytology, which were established between 1865 (when mendel’s work was completed) and 1900 (when it was discovered ).



            Prior to 1900, different theories were proposed to explain inheritance of character in living organism. The earliest, perhaps was the theory of spontaneous emergence of organism from organic matter. Then there was the per formation theory which regarded organism as present in miniature form in one of the gametes, and required only proper nutrition to mature. There was also the theory of epigenesis which attributed the emergence of structures that were not originally present in the individual to some unexplainable force.

            Later on in the nineteen the century, the father of modern evolutionary theory, charles  Darwin, proposed a blending theory (pangenesis )whereby offspring arose simply from a ‘mixing’ of the different characters in their parents. Lamarck’s theory, which followed, proposed that acquired characters were inherited. For example an individual who has one limb amputed as a result produce some offspring with only one limb.

            However, as more advances were made regarding  cell  structure, cell division and behavior of chromosomes, more plausible theories were propounded. One of such theory was Weisman’s ‘germ plasm‘ theory that organisms produces two types of tissues, namely, somatoplasm and germ plasm. The germ plasm transmits hereditary materials from generation to generation. A firm basis for particulate inheritance was provided by the finding of an Austrian monk Gregor Johann Mendel. From his experiments with the garden pea  (pisum sativum), Mendel demonstrated that the appearance of different characters followed specific laws. His findings were published in 1865, but they were however not widely recognized until 1900 when they were independently rediscovered by Hugo Dc vries , CG correns E .tschermak.


Some theories have been developed to back up some of the scientific / experimental findings by contributors. Such theories are;

  1.                       i.        Charles Darwin’s theory –thus, know as the father of modern evolutionary theory, he proposed a blending (pangenesis) whereby offspring arose simply from a ‘mixing‘  of the different characters in their parents.
  1.                     ii.        Lamarck’s theory – He proposed that acquired character were inherited
  2.                    iii.        Hardly –Weinberg law-       It states that gene, and hence, genotype frequencies in a large random – mating population that is not subjected to selection, migration and mutation, remains constant every generation.
  3.                    iv.        Mendel’s experiments with the garden pea gave rise to two fundamental laws of genetics universally known as mendel’s  law. These are the law of segregation and law of independent assortment.

LAW OF SEGREGATION = It states that hereditary characters are controlled by pair of factors’ now called genes, which separate during gamete formation such that only one member of the pair is transmitted by a particular gamete.

Law of independent assortment=It states that members of one allelic pair segregate independently of other pairs and combine randomly to produce different gametes.


The growth and development of a ‘’normal,” “ healthy’’ adult human from a single cell, the zygote or ovum after fertilization by a sperm, is one of the most spectacular phenomena in biology. This complex process requires the coordinated action of thousands of genes. Each of the thousand of genes involved in the growth and differentiation of the multitude of different cell types in the adult organism must be expressed at the proper time and place in the developmental pathway. One fact is very clear. The genes in the human genome are highly co-adapted, and a malfunction in the expression of even a single gene can disrupt the entire developmental process. If the gene  involved  encodes an essential function, its malfunction will be lethal. In many other cases involving important but not absolutely essential (for survivial )  genes, such a malfunction will produce an unhealthy” or” abnormal “ phenotype. Often a defect in a single gene will lead to a whole series of phenotypic abnormalities collectively referred to as a ‘’syndrome’’ one well- known example is congenital hyperuricemia or lesch –Nyhan syndrome .this syndrome is caused by a defect in single gene. New born with this syndrome appear normal but produce excess amounts of uric acid in their urine. By about 10 to 12 months of age, mutilation (teeth,  grinding, lip biting , and so on ) usually ensues. Death often results from severe neurological and renal damage during adolescence.

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            The loss of activity of this single gene  product upsets the normal metabolic balance in the developing infant and leads to the entire array of phenotypic abnormalities. however genetics impacts on health and medical practices at many other levels are far too numerous to describe. One of the greatest successes of modern medicine has been the development of antibiotics to combat disease caused by pathogenic bacteria.

            About hundreds of human diseases are known to be caused by defects in  individual genes. The question is how can these be prevented or treated ? it is hoped that somatic cell gene therapy will provide an effective means  of treatment for some of these diseases in the not too- distant future. All genes have the same basic chemical composition, and all are undoubtedly capable of undergoing mutation to non functional states. Clearly, then, the number of inherited disease in humans will be large, probably on the order of 10,000. With this in mind, one of society’s goal must be to keep mutation rates and the genetic load” ( The accumulation of deleterious mutant genes) in the human genes pool at a tolerable level. To do so, we must minimize the pollination of our biosphere with substances that will increase the frequency of mutations, most notably radioactive agents and mutagenic chemicals.


The contributions of genetics to increased food production is without question, one of the premier success stories of science in the twentieth country. Moreover, the pinnacle of these achievements was clearly the development of hybrid corn. Impressive increases in yield also have been achieved for most of the other important food crops. These dramatic increase in yields of crop plants, collectively call the ‘’green revolution’’, have played a major role in our present ability to feed an over populated world if economic and political systems that would permit adequate world wide distribution of the food produced were in place.

            Although we will never know for certain exactly when human carried out the first “genetic selection” experiments, this probably occurred during the period from 10,000 to 7000(AD) year ago. Fossil records indicates that almost all our present food crops  were domesticated during this early Neolithic period coincident with the development of stone tools. Initially, successful selection was done with no knowledge of the genetic basis of responses that occurred. The largest, more vigorous individuals or those with desired characteristics were simple chosen as parents for subsequent generations. This general approach is still a mainstay of modern plant and animal breeding. However, knowledge about the genetic variability in the population for the trait of interest now permits plants and animal breeding to fine-tune these selection  experiments and to predict the changes that will be realized in response to specific selection strategies.

            The important role of genetics in the achievement of the green revolution is documented by a comparison of the striking increase in agricultural production. Today scientists through the rest of the  world, are performing sophisticated plant and animal breeding and selection experiment that are designed on the basis of detailed information about the genetic control of traits such as yield growth rates in domesticated plants and animal. In addition, scientists are now using  genetic engineering techniques to design crop plants with desired gene such as insect and disease resistance for example, genes from fungi, other microorganisms ,or wild plant species that provide these organisms with resistance to insect pest can now be isolated, tailored for new host organisms by recombinant DNA procedure in vitro- for example, by adding new regulatory elements so that they will be expressed in the proper tissues in the new hosts and introduced into agronomically important domestic plants species by gene transfer technology.

1.6       GENETICS, POLITICS AND LAW.         

            Genetics impacts on all aspect of our live with food production and health being just two of the most important. Recently, genetic has moved front and centre in several area of government and law . the U.S food and drug administration and the U.S department of agriculture have been involved for years in regulating the use of mutagenic chemicals and radioactive substances. With recent revelations of horrendous pollution of the environment by toxic chemical and radioactivity, it is very clear that governments must do a much better job of regulating the use of these dangerous substances. This will only happen if we elect government officials who are knowledgeable of the magnitude of the dangers involved and who will take the actions required to protect the public and all other forms of life as well.

            A second arena in which genetics now plays an integral roles is patent law. The successes of genetic engineering have refocused attention on the question of whether living organisms should be patentable and, if so, within what limits? Plant varieties have been patented for many years with no major controversy, but what about bacteria that have been genetically engineered to degrade chemical pollutants or to make foreign growth hormone? Should they be patentable? The courts have ruled that they are indeed subject to patent protection. The practices of patent law should be a lucrative profession for years to come, and patent lawyers with a background in genetics and molecular biology should be in particularly strong demand. Criminal law is another arena in which the spot light new focuses on genetics. Human ’’DNA prints’’ “or ’’DNA fingerprints’’ are known to posses’ greater specificity by several orders of magnitude than human fingerprints. ’’DNA prints’’ now provide a powerful new tools for establishing identity or non identity in paternity ,rape, and assault cases, as well as all other identity cases where tissue sample might be available linking a criminal to the crime. The DNA printing” approach has become particularly powerful with the recent development of techniques by which small amount of DNA can be extensively amplified in vitro. This allows “DNA prints” to be made even when only very minute amounts of tissue are available.


 Laudable and landmark achievements has been made in the area of genetics. These achievements will be categorically grouped into the following areas;

a)    Human Medicine.

b)    Plant.

c)    Animal.

1.7.1             Human Medicine :- the achievements are as follows;

i)             The determination of genotype and phenotype of an individual.

ii)            Determination on Human “DNA prints” for biological and criminal investigations.

iii)           Detection of blood groups.

iv)           Detection of some genetic diseases or abnormalities such as syndrome, congenital  effects, blood disease (leukemia, anaemia, septicemia, etc.) diabetes, cancer, acquired immunodeficiency syndrome (AID) (caused by retrovirus )etc.

v)            Fluorescence in situ hybridization (fish ) a technique used to identity the presence of specific chromosomes or chromosomal regions through hybridization (attachment ) of fluorescently labeled DNA probes . it provide researchers with a  way to visualize and map the genetic material in an individual’s cells , including specific genes or portions of genes.


vi)           Genetic research has provided geneticists or scientists with the best approach for controlling common diseases.

vii)         Fluoresce in situ hybridization (fish) can be used to diagnose  diseases like praden –will syndrome , Angelman syndrome, 22q 13 deletion syndrome, chronic myelogenous leukemia, acute lymphoblastic leukemia etc.

viii)        Recombinant DNA technology is used in production of chemically active compounds such as hormones, grow factors, anti bodies, vaccines , anti biotics, interferons and thus gene therapy,

1.7.2             PLANT

Research on plants has focused almost exclusively on a few of our most important agromonic crop. More recently, the potentials of genetic engineering of plants has been recognized  and research activities have increased considerably. Plant systems represent a wealth of genetic diversity, and the increased research activities on plants should yield important information about the basic biology of different plant systems as well as some successful commercial applications of genetically engineered plants. Advances made in plant genetics are as follows;

i)             Direct gene transfer, electroporation and microprojectile Guns= It involves the addition of selectable marker genes together with polyethylene glycol (which seems to stimulate membrane fusions)

ii)            Herbicide –Tolerant plant s=when one spray plant (tomato Seeds)  lightly with a solution containing a rapidly degradable broad- spectrum herbicide, the (tomato) plants carry a gene that makes them tolerant to the herbicide while all other plants (weeds) when present in tomato patch are killed by the herbicide.

iii)           Disarmed Ti vectors = once it had been established that the T-DNA region of the Ti plasmid of Agrobacterium tumefaciensis  is transferred to plant cells and becomes integrated in plant chromosomes, the potential use of A. tumefaciaens in plant genetic engineering was obvious. One could introduce foreign genes into the T-DNA region and hopefully, these genes would be transferred to the plant with the rest of the T- DNA segment.

iv)           Disease and insect –Resistant varieties

One goal of plant genetic engineering is to transfer the genes encoding these protein toxins to agronomically important plants with the hope that expression of the toxin genes in these plants will provide biology control of  at least  some serious plant diseases and insect pests.

v)  High-lysine corn.

           Some cereal crops are deficient of some –essential amino acids. For example corn (the seed protein) is deficient of tryptophan and  to a lesser extent of methionine and lysine . Mutants such as opaque-2 sugary -1, and floury-2 have increased amounts of lysine and/ or methionine in seeds.

1.7.3   ANIMAL

            Man relies on plants, animals and microorganism for his daily needs of food, clothing and health care. As a result of this, plant and animal breeders have strived to improve these organism. Methods of improvement have traditionally been by the conventional breeding techniques of selection and mating schemes aided at altering the genetic constitution of these organisms. More recently researchers have developed new techniques which have made it possible to manipulate the genome of living organism. These techniques, which belong to the realm of molecular biology, have resulted in the development of recombination DNA technology or genetic engineering. It is now possible, for example, to extract a DNA sequence or gene from one organism and insert it into another unrelated organism in a functional form. In agriculture, genetically engineered microorganism are being used to produce feed achieves, such as amino acids, vitamins and growth promoters. The greatest potential of this technology in  agriculture is perhaps in the production of genetically engineered plants and animals with desirable characters, for example, incorporation of the growth hormone gene into the genome of domestic animals to improve their growth rate.

There are two processes  involves in genetic manipulation of  animals namely;

Identification and cloning of genes for desired traits, and insertion and regulation of expression of the genes.

(1)       IDENTIFICATION  AND CLONING = genetic engineering of domestic animals must be concerned with those characters that are controlled by single major genes, such as the B21 allele and dwarf gene in poultry, booroola in sheep, and halothane sensitivity gene in pigs. In order to achieve rapid progress in this respect, effort should be geared towards identifying  various biochemical and physiological markers, including restriction fragment length polymorphisms (RELPS) in our domestic animals . These markers will surely facilitate the determination of specific sequence which will be exploited for cloning and subsequent transfer to recipients.

INSERTION AND REGULATION = cloned gene can be transferred to animal genomes either by micro-injection or by the use of DNA and RNA viruses as vectors. Domestic animals reproduce sexually by fusion of sperm and egg cells to form zygote. In order to achieve genetics transformation of these animal by genetic engineering,   foreign DNA or gene must be inserted into the sperm, ovum or early embryo. Genetics in pisces (fish ) as vertebrate are not left behind. However huge level of progress has become recorded in the genetics of fish and this will form a major area of interest of these works.


The application  of genetics in the study of fish can be described as fish genetics. It is done to improve or achieve a desired traits  or characters in fish. Such traits are; better quality of meats better growth rates and survivals, production of hybrids, better tolerance for reduced level of oxygen and salinity etc. fish genetics seek to understand and identify the genetics of fish .


            The beginning of fish genetics in brazil in a permanent and organized way involves research developed early in the sixties by silvio de Almeida Toleda Filho at the bioscience institute of the university of sao Paulo, a research who, is perhaps the most important person in the field of fish genetics in brazil ever since the early years of this discipline. Silvo’s research on fish genetics began in the late 1960’s when ove Fryden bery from Denmark, recognized his work on protein electrophoresis and its application to population genetics of Atlantic cod visited brazil. Protein electrophories generated much interests among brazilian researchers  and was a quickly  adopted techniques  that resulted in  the establishment of new research option for laboratories devoted to the study of fish populations. This important research groups in fish genetics were established in Rio Graude do sul by professor Jose levy, in Amazonia by professor Aylton Teixeira, and in parana by professor Emesto Renesto, etc many of these researchers and members of their group have continued to use the protein electrophoresis techniques, even up to this day, for the resolution of fish genetics problems.


Fish genetics has provides researchers with information on how best to improve, in the various areas of fisheries and in the studies of fish population advances in fish genetics are to be discussed below


            It is defined as the introduction of exogenous gene/ DNA into host genome resulting in its stable maintenance, transmission  and expression. The technology offers an excellent opportunity for modifying or improving the genetic traits  of commercially important fishers, mollusks and crustaceans for aquaculture.This idea of producing transgenic animals became popular when palmitter et al. (1982), first produced transgenic mouse by introducing metallothionaum human growth hormone fusion gene (Mt-hGH) into mouse egg, resulting in dramatic increase in growth. This triggered a series of attemptson gene transfer in economically important animals including fish. The first transgenic fish was produced zhu et al. (1988) in china, who claimed the transient expression putative transgenic, although they gave no molecular evidence for the integration of the transgenics. The techniques has now been successfully applied to a number of fish species. Dramatic growth enhancement has been shown using this technique especially in salmonids (Devlin et al. 1994). The introduction of transgenic techniques has simultaneously put more emphasis on the need for production of sterile progeny in order to minimize the risk of transgenic stock mixing in the wild populations. Although significant progress has been made in several laboratories around the world, there are numerous problems to be resolved before the successful commercialization of the transgenic brood stock for aquaculture. To realize the full potential of the transgenic fish technology, several important scientific break through are required. These include;

  1.                                 i.        More efficient technological mass gene transfer.
  2.                               ii.        Targeted gene transfer technologies such as embryonic stem cell gene transfer.
  3.                              iii.        Suitable promoters to direct the expression of transgenic at optimal levels during the desired development stages.
  4.                              iv.        Information on the physiological, nutritional, immunological and environmental factors that maximize the performance of the transgenics.
  5.                               v.        Safely and environmental impact of transgenic fish.
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            Biotechnological tools such as molecular diagnostic methods ; use of vaccines and immunostimulants are gaining popularity for improving the disease resistance in fish and shell fish species world over for viral diseases, avoidance of the pathogen is very important .


            Chromosome sex manipulation techniques to induce polyploidy (triploidy and tetraploidy ) and uniparental chromosome. Inheritance (gynogenesis and androgenesis ) have been applied extensively in  cultured species (pandian and koteeswaran, 1998,lakra and Das 1998). These techniques are important in the improvement of fish breeding as they provide a rapid approach for gonadal sterilization, sex control improvement of hybrid viability and clonation. Vertebrates are diploid, meaning  they possess two complete chromosome sets in their somatic cells. Polyploidy individuals possess on or more additional chromosome sets, bringing the total to three in triploids, four in tetraploids and so on. Induced triploids is widely accepted as the most effective method for producing sterile fish for aquaculture and fisheries management.The method used to induce triploids and other types of chromosome set manipulations In fishes and the application of these biotechnologies to aquaculture and fisheries management are well described (purdom, 1983; chowrout 1987; thorgaard, 1983; pandian and koteeswan, 1998).

2.4       Crypo preservation of gametes and gene banking

            Crypopreservation is a techniques which involved long- term preservation and storage of biological material at a very temperature usually -1960C ,  the temperature  liquid nitrogen. It is based on the principle that very low temperature tranquilize or immobilize the physiological and  biochemical activities of cells, thereby making it possible to keep them viable for very long period. The technology of cryopreservation of fish spermatozoa (milt) has been adopted for animals husbandry. The first success in preserving fish sperm at low temperature was reported by Blaxter (1953 ) who fertilizes herring (clupaherengus ) eggs with frozen thawed semen. The spermatozoa of almost all cultivable fish species has now been cryopreserved (Lakra 1993). Cryopreserved overcome problems of male maturing before females allows selective breeding and stock improvement and enables  conservation (Hawey,1996). one of the requirement for that can be used by breeders for evolving new strains. Most of the plant varieties that has been produced are based on the gene collections.

2.5       INTERGENRIC HYBRIDIZATION =It consists of crossing fish belonging to different species. This is done to unite the useful characters of two different species in one of the new forms and to produce a new construction in consequent of the heterosis effect. Result of intergeneric hybridization are;

  1.                   i.        New construction with new feeding habits for composite  fish culture or for water reservoirs.
  2.                 ii.        Better growth rates and survivals.
  3.                iii.        More restful behavior, having better tolerance for reduced levels of oxygen (silvercarp x big head).
  4.                iv.        Better quality of meat (common carp x silver carp).
  5.                 v.        Monosex triploid grass feeder fish (grass carp x big head).

2.6       Artificial Gynogenesis And Hormone Sex Reversion

               The main purpose of gynogensis is to produce inbreed individuals having only maternal chromosomes for the further genetics work. For causing gynogenesis  artificially, inactivated sperm can be used for fertilization of eggs, with a cold shock treatment after fertilization. For the inactivation of sperm, a cobalt 60 gamma ray source of ultra-violet germicide lamp has to be used. The genogenetic populations are female with diploid chromosome sets similar to the mother. The technique of artificial gynogenesis was demonstrated on the common carp. For producing gynogenetic inbreed male populations, methyl testosterone hormone feeding has to be provided for the sex formation in direction of the male. For the purpose of increasing the inbreeding level, the gynogenesis  can be applied from generation to generation. It is important to make a proper selection within the gynogenetic population to avoid the undesirable effect of inbreeding depression.


These investigation are aimed at finding and using genetic markers for character and identification of fish populations and individuals. Such markers are the enzyme and proteins, including transferrins.the instrucment foer this method is th polyyacrilanad gel – electrophoretic equipment which was ordered.


Good results have been achieved so far such as;

  1. Analysis of chromosome sets and karyotypes
  2. Crossing the species, using artificial propagation
  3. Studying the fish species character, behaviour and genetic structures.
  4. Rearing the hybrids in the most suitable environment for their expected habit.
  5. Describing the new hybrids morphological, biological and economic characteristics.
  6. Stabilizing the new character with inbreeding or back- crossing with the closer parental species which are similar in their main characteristics to the new hybrids.



The birth of genetics brought to the understanding of human resemblance, population, hereditary issues and their connectivity from generation to generation. Genetics findings have no doubt, solved and answered so many questions such as nutrition, biology and physiology of cretures. It has helped in identifying  and improving the biology of human, animal and plant nature. Advances in fish genetics has led to the enhancement and achievement of desired characters in fish such as production of quality fish for consumption, breeding and resistance purposes, hybridization, controlled characters, mono sex cryopreservation of gametes etc. with this, one is able to understand the rudiments and principle of genetics.

I  recommend that more incentives should be provided especially in the area of funding for more sophisticated genetic researches and instrumentations .


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