The pioneer and father in the study of genetics was Gregor Mendel (1822-1884), an Austrian monk. Mendel studied the cross breeding of common peas in the monastery’s garden. Mendel’s brilliance along with his innovative interpretation of the data collected is considered to be one of the greatest intellectual achievements by an individual in the history of science!
The pioneer and father in the study of genetics was Gregor Mendel (1822-1884), an Austrian monk. Mendel studied the cross breeding of common peas in the monastery’s garden. Mendel’s brilliance along with his innovative interpretation of the data collected is considered to be one of the greatest intellectual achievements by an individual in the history of science!
Mendel worked on his theories of inheritance long before there was any evidence of the existence of chromosomes and genes. For 8 years he studied certain traits of the common pea plant, Pisum sativum .
Mendel studied seven traits of Pisum sativum, each group of which had two different, distinct set of characteristics:
* seed color (yellow or green)
* seed coat (round or wrinkled)
* flower color (Purple or white)
* pod shape (inflated or constricted)
* stem length (long or short)
* flower position (axial or terminal)
* pod color (green or yellow)
First Mendel collected the seeds in groups of “Pure Parent” plants with the above characteristics. These were the plants whose offspring consistently possessed the given trait through successive generations. For the experiment on pea seed color, Mendel selected one group of plants that consistently produced offspring which only produced yellow seeds and those which only produced green seeds. He did the same with each of the 7 different groups giving him a “Pure Collection” of 14 different seeds.
Once he had his “pure parents,” Mendel crossed the two groups of plants. He took pollen from one of the groups and pollinated flowers on the other group, and vice versa. He took great care of the plants and carefully nurturing them until the pods were fully mature. Once the enclosed seeds were mature, he harvested the seeds noting the colour of the seeds from each plant. He planted the seeds from the F1 generation and let these new plants grow to maturity. He referred to these first offspring, produced by crossing two pure parents as the F1 being short for First Filial Generation.
Mendel found that all of the F1 generation had yellow seeds. He repeated the experiment with hundreds of plants where the results were the same.
Mendel then planted these F1 plants of yellow seeded peas and allowed them to self pollinate. Again, he let the seeds mature, harvested them, and recorded the seed color of the different plants. This second generation of offspring he referred to as the F2 generation.
After harvesting and counting the plants he found that three in four of the plants in the F2 generation had yellow seeds while 1 in 4 or 1:3 ratio of the plants had green seeds.
From these results, as well as the results from experiments on other plant traits over the following 8 years, Mendel came to the conclusion that there were two “hereditary factors” for every plant trait studied.
He proposed that one of the hereditary factors was dominant over the other one. He termed the trait that was visible in the first crossing (the F1 generation) the dominant trait. The trait that was not visible in the F1 generation, but that reappeared in the F2 generation, he called the recessive trait. With all of the seven pea plant traits that Mendel examined, one form appeared dominant over the other, which is to say it masked the presence of the other allele. For example, when the genotype for pea seed color is YG (heterozygous), the phenotype is yellow. However, the dominant yellow allele does not alter the recessive green one in any way and both alleles can be passed on to the next generation unchanged.
Mendel further theorized that during the formation of egg and sperm, these hereditary factors are segregated from one another. The parent plant has two hereditary factors, but only one of each pair goes to each gamete produced.
Then, during fertilization, two gametes unite. The egg donates one hereditary factor; the sperm the other, so the resulting zygote, like the parent plants, contains two hereditary factors. Mendel concluded that a recessive factor can be carried through a generation unchanged, even when it is not visible. Mendel’s Principle of Segregation explains how a trait can be hidden without being eliminated from the equation.
Mendel then planted these F1 plants of pink flowers and allowed them to self pollinate. Again, he let the seeds mature, harvested them, and recorded the seed color of the different plant’s flowers. The F2 generation plants had a ratio of 1:2:1, that is there was 1 white flower, 2 pink flowers and 1 red flower.
Snapdragon flower colour genes displayed what is now known as incomplete dominance where neither gene is dominant nor recessive. Mendelian genetics ultimately revolutionized the science of biology and provided support for Darwin’s theories of natural selection.
Plant Breeding
Artificial selection: Once humans realized this earnest programs began selecting and saving particular seeds. They began the process of crop improvement. By carefully observing growing crops and choosing seeds from the best plants to save for the following season, farmers slowly improved production, taste, pest resistance, and/or other features of their crops to our satisfaction not necessarily to the plants environmental advantage. This opposes the evolutionary process of natural selection, where the “fittest” survive and reproduce, this type of crop improvement allows farmers to encourage plant qualities that they consider important. Throughout much of the long history of agriculture, this was the only method of improving crop plants.
Hybridization: Once the fundamentals of plant reproduction were better understood, the science of plant breeding began to emerge with hybridizing. Early plant breeders identified desirable characteristics, and carefully cross pollinated plants in the hopes of bringing these characteristics together in one plant. This technique is slow and requires patience and precision. A cross-pollinated plant might produce hundreds of seeds, and each of these would be planted. The new seedlings would be nurtured to maturity and, once again, those with the most desirable traits would be selected. This process would continue until a suitable plant was found. The breeders would then begin the task of propagating the suitable plant to produce commercial quantities of seed.
Organic agriculture : Critics claim it is too low yielding to be a viable alternative to conventional agriculture but have they stopped to think about their claims and what resources have been allocated to the Industry? Maybe part of the lowers yields can be contributed to the growing of poorly adapted varieties after all the chemical industry and governments have favoured and concentrated almost entirely on chemically produced foods and clothing with very little assistance being given to the Organic industry. It is estimated that over 95mm of organic agriculture is based on chemically adapted varieties at the expense of the environment, health of the farmers or production even though the production environments found in organic farming compared to chemical farming systems vary vastly. They are different due to their distinctively soft management practices and a more balanced approach to soil management compared to soils that are high in chemical fertilizers, excess water and higher volumes of toxic residues. Breeding varieties specifically adapted to the unique conditions of organic agriculture is critical for this sector to realize its full potential. This requires selection for traits such as compared to the chemical farmer’s crops that may be bred for resistance to herbicides, to utilize higher concentrates of fertilizers or even insecticides:
* Water use efficiency
* Nutrient use efficiency particularly nitrogen , phosphorus & potassium.
* Weed competitiveness
* Tolerance of mechanical weed control
* Pest/disease resistance
* Early maturity (as a mechanism for avoidance of particular stresses)
* Abiotic stress tolerance (i.e. drought, salinity, etc…)
There is very little if any breeding program is directed at organic agriculture and until recently those that did address this sector have generally relied on indirect selection using selection from chemical environments for traits considered important for organic agriculture. However, because the difference between organic and conventional environments is large, a given genotype may perform very differently in each environment due to an interaction between genes and the environment. If this interaction is severe enough, an important trait required for the organic environment may not be revealed in the conventional environment, which can result in the selection of poorly adapted individuals. To ensure the most adapted varieties are identified, advocates of organic breeding now promote the use of direct selection or selection in the target environment for many agronomic traits. This is presently done and paid for by the individual farmers.
In my own case we initially planted 15 varieties of citrus and after 5 years in our district realized 2 varieties outstripped all the other varieties and 1 was equal to other chemically laced orchards in the district. 1 of these varieties only displayed excellent results after we planted the remaining orchard out with the first type. The second variety which had high yields that proved itself later did so in drier weather conditions and as the trees matured. Against this we made further plantings of a lemon variety which also proved highly profitable but sensitive to environmental factors where we had to be very specific in its allocation and position. This was a cost born by us not the government’s agricultural department.
Hybrid Vigor :The increase in vigor, size, fertility, or other positive characteristic of a hybrid compared with its parents. You may have heard the term hybrid vigor. Selected hybrid plants are more uniform than non hybrids in production. Also, hybrids sometimes exhibit dramatic improvements in yield, size, disease resistance, or other desirable features when compared with the parent plants. Scientists do not know exactly why this occurs, but suggest that it may be stimulated by the mixing of the very different gene pairs of the parent plants.
Biotechnology- GMF Breeders sometimes cross crop plants with some of their wild ancestors, hoping to impart the ancestor’s desirable features, such as disease resistance or hardiness, without losing the current variety’s palatability or yield. Considering that very few crossings actually result in progeny showing significant improvements over the parent plants, and how time consuming and tedious the process is, the accomplishments of plant breeders are all the more remarkable.
Genetic Engineering is a new and often misunderstood technology that will certainly be in the news for years to come. This is not a natural phenomenon but as it states Engineered or MANipulated by large companies to increase profits with no consideration apart from legislation for the environment or human safety. Beware of false statements like increased production, decrease in herbicides or insecticides use or decrease in the quantity of fertilizers used. These same companies are selling the other products like fertilizers, insecticides and herbicides so are unlikely to sell a product that will lose them sales in another area. Glyphosphate resistant soy beans only meant that more of the chemical could be used on their already failing hybridized crops than before. It is the easy, profitable way out for the companies not the safe long tern way of the future.
* 1850’s Cross pollination between varieties of the same species like in wheat to gain an advantage in a particular direction in a particular location leaving the diversity in tact.
* 1930’s Hybridization between different species. e.g. wheat + rye = triticale
* 1975 Cell fusion to overcome species barriers by combining individual plant cells so that hybridization between different species and genus could be undertaken.
* 1985 DNA Technology is the addition or modification of crop characteristics at the level of individual genes.
Cell and molecular biology have allowed scientists to remove a portion of a chromosome from one species and place it into another organism. This type of cell manipulation has dramatically accelerated the world of plant breeding without long term consideration.
Remembering Chapter 1 we learnt about bioendosymbosis. Is GMO the start of a new resistant bioendosymbosis? It only takes one, it only needs one and it may be too late the planet maybe changed for ever unfit for human beings. After all it started with 2 bacteria one consuming another two separate genes one inside the other and the gene pool was altered for ever.
Company representatives like to refer to it as saving time rather than crossing and growing out generation upon generation upon generation of bean plants, for example, when in essence you simply splice the desirable genes into the bean cell. This single cell is then placed in a special nutrient medium that stimulates it to begin dividing; eventually the cells begin to differentiate and a complete plant is formed. Because the genetic material is contained in the initial cell, the new genes are incorporated into every new cell. If it is so simple and beneficial why hasn’t nature afforded this naturally?
Plants and foods created using this technology are known as transgenic bioengineered, genetically engineered or Genetically Modified Foods GMF. In contrast to performing conventional plant breeding, scientists can now take genes from virtually any living organism and insert them into another totally unrelated organism even from animal to plant.
This poster said it all The Food Chain in action Grow a GMO corn and the insect dies. What it does not show is alarming. A bird eats the insect and also accumulates the poison; not necessarily Bacillus thuringiensis, or a human eats the corn and accumulates the poison. After all DDT was once considered harmless as was arsenic on bananas.
The noticeable omission is many years ago farmers were told poisonous sprays would solve the insect problem. Did it? No. Insects that were on the front line and being targeted slowly built up immunity to the poisons. So the chemical companies made stronger poisons and governments raised the safety levels where farmers could not add more. The next solution and we were sold on the benefit no drift, no soil contamination accumulation with GMO’s. An admission that what they were doing was not in my view entirely ethical. The fact is the insect being targeted will sooner or later build up a defence immunity to the GMO crop or another unbeknown insect will step into its place. genetics is at work everywhere. I grew a number of Sterculia quadrifolia trees from seed.
Expecting them to flower in their 4th to 6th year, I had one tree that flowered when it was n the pot at six months of age and at just 300mm in height. That was 1:8 plants.to allow it develop could have affected the local populations so we did the correct thing and killed it. The other trees all grew as normal. my argument is there is a gene pool out there in the form of natural predators. we are far better off utilising nature and them to combat the peril.
The possible uses for this technology are “limitless”. I once read “For example, if scientists were able to transplant the genes that allow peas to fix nitrogen from the atmosphere into corn or tomato plants, there could be a dramatic reduction in the need for fertilizing with nitrogen. This would impact water quality by reducing fertilizer runoff and help farmers unable to afford synthetic (chemical) fertilizers. Where is the profitability here for the companies to market such a crop?
Remember:
1. “Pure Parent Traits” could be maintained over successive generations even with cross pollination occurred.
2. An F1 plant is short for First Filial Generation while subsequent generations are known as F2, F3 etc.
3. The trait that was not visible in the F1 generation, but reappeared in the F2 generation is known as the recessive trait while the dominant trait is visible in the F1 generation.
4. The principle of Gregor Mendel theory of Segregation explains how a trait can be hidden without being eliminated from the equation.
5. The F1 generation of dominance and recessive traits in organisms all display the characteristics of the dominant gene while the recessive genes are hidden or masked.
6. The F2 generation plants have a ratio of 3:1. 3 dominant to 1 recessive plant.
7. The F1 generation plants with co dominant genes have a mixed or blending of characteristics.
8. The F2 generation plants with co dominant species have a ratio of 1:2:1, that is there is one dominant plant, 2 blended gene plants and 1 recessive gene plant.
9. Hybridization is the cross breeding of 2 different species in order to gain a horticultural advantage over the parent plants.
10. Genetic Engineering is not a natural phenomenon but as it states Engineered or MANipulated.
11. Plants and foods created using this technology are known as transgenic bioengineered, genetically engineered or Genetically Modified Foods – GMF.
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