GENETICS AND AGRICULTURE (Definition And Examples)

 


If a cross is made between a variety of maize plant with yellow grains and one with purple grains, the F, generation all have purple seeds. If the plants grown from these seeds are cross pollinated, the cobs of the F2 generation will look like those in. These results indicate that the grain colour is controlled by a single pair of genes of which the gene for purple is dominant. The F, plants are called hybrids because they are produced by crossing different varieties. It has been found that when two pure-breeding lines of maize plants are cross pollinated, the F, hybrids often give a much greater yield of grain than either of the parent varieties. The plants from the hybrid grain do not, however,  Therefore it is necessary for specialist seed producers to make the initial crosses and sell the F, grain to the farmers. AA knowledge of genetics can be used in this way to improve the yields of both plants and animals and also to introduce desirable characteristics such as disease resistance into a stock.

By a series of hybridizations the genes for resistance to a fungus disease in a wild grass Aegilops ventricosa have been introduced into a variety of wheat so that the final hybrid is both high yielding and disease resistant. With cotton plants, programmes of hybridization have enabled plant breeders to introduce genes for resistance to bacterial and virus disease. Cotton grown in the Sudan is particularly prone to a leaf curl virus and a bacterial infection called blackarm. From varieties already in the Sudan, it was possible to introduce genes for virus resistance but the genes for resistance to the bacterial disease had to be incorporated by crossing with a species of cotton from Central America.

Similar principles can be applied to farm animals. In most cases the hybrid ofispring are intermediate between the two parental types for characteristics such as milk yield, fertility growth rate and mortality rate. In some crosses of cattle, however. the F, hybrids have proved to have significantly higher fertility and reduced mortality rates; in other words they produce more offspring and are less prone to diseases.

Nevertheless, there is evidence that, in dairy cattle at least, the variation in, say, milk yield between herds of the same breed is 75 per cent due to management and environmental conditions and only 25 per cent is attributable to genetic differences The disadvantage of hybrids is that they do not breed true.

The desirable characters combined in the hybrid organism tend to segregate out at meiosis. For a long-lived hybrid organism such as a cow this is not so important but for plants it means that fresh hybrid seed must be obtained for each planting Alternatively the desirable characteristics of the hybrid must be preserved by vegetative propagation Inbreeding, that is, consistent self pollination with plants or brother-sister matings in animals produces pure-breeding lines with predictable offspring but also results in some falling off in yields or disease resistance, perhaps because of the accumu- lation of a number of undesirable genes in the homozygous condition.


GENETICS AND AGRICULTURE (Definition And Examples) GENETICS AND AGRICULTURE (Definition And Examples) Reviewed by Admin on July 09, 2022 Rating: 5

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