Question

15.a) What is the difference between a discrete polymorphism and a continuous trait? Provide an example of each. 15.b) What are the three sources of phenotypic variation in a population? Explain your answer using an example (real or imaginary).

Answer 1

Answer:

(a) Polymorphism is referred to the presence of two or more phenotypes that exists in a same population of a particular species, it simply means there is an occurrance of more than one form or Morph. This is a result of an evolutionary process. This is heritable and are modified during the natural selection process. Usually polymorphism deals with the forms where the variations are seen in the form of discrete or polymodal or bimodal.

Polymorphism helps in promoting diversity and usually persists over many generations, this is because no single form have the capability or disadvantage over the others in the terms of natural selection.

The discrete or discontinuous traits are controlled by small number of genes(often one). In other words, it means that the traits that have only few possible phenotypes fall under this category. Discrete, or the discontinuous traits are usually controlled by a small number of genes. These genes generally have two alleles. For example, Mendel’s pea seeds had two alleles for shape: smooth or wrinkled. Discontinuous variation is mainly controlled by alleles of a single gene or a small number of genes. There is no or little effect of environment in these type of traits. Individuals of these group fall under different groups and their features cannot be measured over a wide range.

A continuous trait on the other hand is a range of expression (such as height,weight, etc.) rather than an all-or-none appearance (such as white or red). Continuous traits are usually under polygenic control and they are subject to changes in the environment. This is basically a combined effect of many genes i.e., polygenic inheritance and they are significantly affected by the environmental factors.

(b) Phenotypic Variation:

Phenotypes can be defined as the traits of features of an organism that can be obeserved(such as colour,size,shape etc). Phenotypic variations is referred to as the variations that can exists in a population. There are basically two types of phenotypic variations:

(i) characteristics that varies continuously and the

(ii) phenotypes that are discontinuous.

Phenotypes varying continuously, the characteristics or the phenotype usually exists in a range or gradient. In contrast the phenotypes that are discontinuously varying exists only at the discrete intervals

Sources of variations:

• Random mutations are the ultimate source of genetic variations. The mutations are rare and most of them are either neutral or deleterious but in some cases the new alleles are favoured mostly by natural selections.
• For example: Polyploidy is an example for the genetic variations caused which is a great example for chromosomal mutations. This is a condition where the organisms usually posses three or more sets of genetic variations.
• Other source is crossing over causing genetic recombination and the random segregation during the meiosis. This can result in the production of new or new combination of alleles.
• Random fertilization also plays an major role in variation