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Science & Technology
Mendel's breaks through in Genetics


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Science & Technology
Special Report

We should strengthen our efforts on bio-fertilizers and bio-pesticides

By Dr. S. M. ALAM
Nuclear Institute of Agriculture, Tando Jam
Sep 18 - 24, 2000

Life of any type on our earth really appears to be in an infinite variety of forms and is represented by a very large number of man, plant and animal species. Among animals alone the number of known species exceeds more than a million. Each individual species of man, animal or plant has unique characteristics. One of the main tasks of genetics is to clarify the really strange fact that why life appears in so many different forms. Another major good genetics is to analyze or examine the causes of similarities between parents and offspring. Individual peculiarities of the parents often reappear with great sharpness in offspring. A common but fascinating experience is to observe that our children are similar to us or to other close relative with respect to their physical and their mental properties. It has been assumed that modern genetics is a rather young science, but speculation concerning the nature of heredity have been made as far back it is possible to trace in our cultural history. These speculations are in part founded on observations or speculation in man, partly upon experiences gained from plant cultivation and animal breeding. Charles Darwin (1809-1882) a famous English naturalist completely dominated biological thought during the later half of the 19th century and that his publications and theories entirely overshaded the apparently modest experiences of one of his contemporaries, Gregor Johann Mendel (1822-1884) an Augustinian monk or a clergyman, who lived in Brunn, Austria (now Brno Czech). Mendel's results were destined to become of fundamental importance for genetics in our time. Mendel demonstrated that the hereditary substance was not a uniform extract of the body cell, but was composed of many independent and constant hereditary unit, which are transferred from one generation to the next. During this transfer, the hereditary unit would be regrouped, in this way giving rise to a high degree of biological variation in the system of the body cell. As a scientist Mendel performed several experiments, but his main material consisted of different pea varieties which in cultivation were found to be constant, but differed in single conspicuous characters. Certain varieties had yellow seeds, others green seeds, the seeds could be round or wrinkled, the flowers white or coloured, the pads yellow or green and so on. Mendel once succeeded in obtaining such pairs of contrasting characters that were found to be conditioned by allelic genes. From several crosses, he found that the hybrids were not at intermediate between the parents, but in most cases corresponded to one or the other of them. For this reason, he introduced the term dominant and recessive, frame the experimentally induced hybrids (F1 generation). Mendel raised progressively self- pollinated and found that these progenes (F2) were by no means, uniform and constant. On the contrary, some of the plants showed the dominant character the recessive one.

Mendel counted the number of individual of these categories and find that on an average, three fourth of a progeny had the dominant character, one found the recessive one alone he raised one more generation (F3), he found that the recessive F2 plants gone offspring that only displayed the recessive character. In this way Mendel collected very reliable and comprehensive data.

Transmission of hereditary substance: It has been realized since time immemorial that the similarities between parents and offspring must be due to some kind of hereditary substance, which is transmitted by the sexual products. That the mother puts her mark on the child is easy to imagine, but it is more difficult to understand how the child can inhered the properties of the father just the same high degree as those of the mother. Nowadays, unfortunately, we know certainty what happens, but not until 1875 did not become definitely clear that the true essence of the process of fertilization is the union of the female and male sex cell. More precisely fusion occur between the nuclei of these cells and in this way their chromosomes are brought together.

Genes, alleles and multiple alleles: It has been established that chromosomes are linearly differentiated and the genes are arranged in sequence like beads of necklace. The site in a chromosome where certain gene is located is called a locus. Now it has been found that in certain cases a locus may be the site a gene that is exactly the same in all chromosome of this kind within a species or group of individuals. In many cases, however, a locus does not display this absolute constancy but may be the site for either one of a number of genes. Often only two different alleles are known for certain locus. In other cases it may be a question of a whole series of different gene expressed states and in these cases we are dealing with multiple alleles.

Discovery of stable genes: ended realized that his results could only be explained by the assumption that the hereditary differences between the intercrossed parents depend on individual, constant units of heredity later on called genes, which in an unchanged condition are transmitted by the sex cells from one generation to the next. That a hybrid forms more than one kind of sex cells and that the dominate and recessive genes are distributed with equal frequencies in the male as well as in the female sex cells represent the central point of Mendel's discovery.

The genes in these combinations are exactly the same as the previous ones, but they have been regrouped and this regrouping or recombination has led to the origin of new individuals from which new true-breeding varieties with new constellation of characters can arise. Still more important but just as simple is the formula 3n in which (n) again indicates the number of genes for which a certain hybrid is heterozygous. This formula denotes the number of genetically different combinations in the offspring of the hybrids. In mono hybrid segregation n=1 and 3=3. This is indeed true because in the F2 according to the formula 32=9. With trihybrid segregation, 33=27 genetically different categories are formed. And with higher revalues the degree of genetic variation is enormously increased. If n is 10, 310=59,049 different combinations of genes may be formed and if n is 50 or 100 we obtain astronomically large numbers. The country made tremendous success during the Green revolution era in early 60's and food production has increased to almost double from the level of 70's. Cropping intensity has increased considerably with the help of modern inputs. However, the present trend is not very bright as in the past. The demand of cereals is increasing day by day due to increase in population growth. There will be demand of food products of animal origin, such as fish, meat and chicken. Poverty is also a serious problem in the country. Lower productivity of crops is the root cause of poverty, leading to want to exploitation of the natural resources. The country's agriculture will have to strike for greater global competitive in agricultural production and marketing. Although, the challenges are many and complex. The proper utilization of science-based knowledge will help to surmount the challenges. We have to utilize the frontier technologies available in the world to the problems. Awareness among the users must be made to get the full benefit of those research output so that the gap between the potential and actual yield is minimized. Conventional breeding systems will play a key role in enhancing the yield potential of modern varieties but the availability of aid lunching tools of biotechnology would accelerate development in the transfer of genes from one species to another. Utilization of knowledge of intensive technology like bio-fertilizers, integrated pest management, integrated nutrient management system should be introduced at an accelerate rate. Bio-fertilizer is a cost effective and renewable source of plant nutrients to supplement chemical fertilizers. We should strengthen our efforts on bio-fertilizers and bio-pesticides. Wild plants and traditional cultivars among other biological resources, represent raw genetic material for crop improvement and plant-based industry. Pakistan has quite high biodiversity. Efforts should be made to use modern tools for the conservation of endangered plant species. Today, the world of sciences are very much competitive, we should have more frontier knowledge on molecular biology, biotechnology, nuclear science, biomadies etc.