INTRODUCTION TO GENETICS

Genetics

Introduction to Genetics:

A person's eye can be blue, brown, green, gray, or hazel; a person’s hair can be different shades of brown, red, blond, or black; a parakeet’s feathers can be green, blue, or yellow, with black or gray markings. What causes these biological spectra of colours? We can frame the question in more general terms: What is genetic basis of variation among a population's individuals? Or, what principles account for the transmission of these variations from parents to offspring?

One possible explanation of heredity is a “blending hypothesis”, the idea that genetic material contributed by two parents mixes in a manner analogous to the way blue and yellow paints blend to make green. The hypothesis predicts that mating a blue parakeet with a yellow one would result in green offspring, and once blended, the hereditary material of the two parents would be as inspirable as the colours of mixed paint. If the blended hypothesis were correct, over many generations a freely mating population of blue and yellow parakeets would give rise to a uniform population of green birds. The actual results of parakeet breeding, however, contradict such a prediction. The blending hypothesis also fails to explain other phenomenon of inheritance, such as traits skipping a generation.

An alternative to the blending model is a "particulate model" of Inheritance: the gene idea. According to this model, parents pass on discrete heritable units – genes – that retain their separate identities in offspring. An organism's collection of genes is more like a bucket of marbles than a pail of paint. Like marbles, genes can be sorted and passed along, generation after generation, in undiluted form.

The first scientific advance in the study of inheritance was made by the Austrian monk Gregor Mendel who published a paper in 1866 which laid the foundations for the present-day science of genetics. He demonstrated that characteristics do not blend but pass from parents to offspring as discrete units. These units, which appear in the offspring in pairs, remain discrete and are passed on to subsequent generations by the male and female gametes which each contain a single unit. The Danish botanist Johannsen called these units GENES in 1990 and the American geneticist Morgan in 1912 demonstrated that they are carried on the chromosomes. Since the early 1900s the study of genetics has made great advances in explaining the nature of inheritance at both the level of the organism and at the level of gene.