Natural selection under different environments condition, Biology

Assignment Help:

In the absence of any large scale envirorrmental change that is, in more or less uniform environments, populations often maintain a stable genetic constitution with respect to many traits. Natural selection in the absence of environmental change maintains a genetic homeostasis. This phenomeon is known as normidising selection Several of the phenotypic, traits of individuals can be arranged on a linear scale. The distribution curve of the traits usually takes a bell shape, so that the number of individuals is greater at intermediate values and gradually decrease towards the extremes. Ja. As stated earlier, normalising selection occurs when individuals with intermediate phenotypes are favoured and those with extremes are under selection pressure. This tendency continues generation after generation. If there is a strong selection pressure against the phenotypes occupying the extremes of normal curve, then the population may show less variability although the mean remains the sarne. Natural selection has more often a normalising or stabilising effect on populations with mid-values for the traits and individuals with intermediate values for their traits have better chances of survival. For instance, new born infarits which weigh very less or very more than the average weight have high rate of mortality. Contrarily infants of intermediate weight have less problems of survival. We discuss two examples below, one from nature and the other from the experiments of Dobzhansky and Spassky to explain the concept of normalising selection.


Related Discussions:- Natural selection under different environments condition

Problems with untreated/ammoniated crop residues, Problems with untreated/a...

Problems with untreated/ammoniated crop residues Besides the low energy and protein contents, crop residues generally contain low content of minerals such as Calcium, Phosphor

Homopolysaccharides, HOMOPO L YSACCHARIDE S (= HOMOGLYCANS) These...

HOMOPO L YSACCHARIDE S (= HOMOGLYCANS) These are complex carbohydrats that are formed by repeated condensation or polymerisation of only one type of monosaccharide monome

Coelenterata, mode of digestion in coelenterata

mode of digestion in coelenterata

Osmosis, everything about osmosis

everything about osmosis

Differences between budding and fission, Differences between Budding and Fi...

Differences between Budding and Fission Both budding and fission are identical in at least one way in that the young ones produced by these procedures are the result of direct

What are the functions of the spleen, Q. What are the functions of the sple...

Q. What are the functions of the spleen? Why is a total splenectomy (surgical removal of the spleen) compatible with life? The spleen has many functions: it participates in the

Nutrient elements of plants, Nutrient Elements of Plants Let us first ...

Nutrient Elements of Plants Let us first find out the chemical composition of plants and see which element nature has selected to support their healthy growth. Only then we wi

Classification of nephrotic syndrome, Classification of Nephrotic Syndrome ...

Classification of Nephrotic Syndrome In childhood, nephrotic syndrome can be divided into minimal lesion nephrofic syndrome and  significant lesion nephrotic syndrome dependin

Define changing body composition - age related functional, Define Changing ...

Define Changing Body Composition and Techniques for Measuring Body Composition? Changing body composition has been suggested as a pathway to explain age-related functional decl

Effects of cardiac output and hormones, Excluding the effects of cardiac ou...

Excluding the effects of cardiac output and hormones, describe the other factors that may affect blood pressure and blood flow in a middle-aged man who is exercising in an aerobics

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd