Environmental Effects on phenotype

Environmental Effects:

Effects of External Environment:

External environmental effects lead to phenotypic changes that seem directly correlated with observable changes in the surrounding of an organism. These are influenced by the following factors:

1. Temperature: Changes in temperature may result in changes in the degree of expression of a gene. It may activate or inactivate a gene.

2. Light: The seedlings grown in dark do not develop chlorophyll and appear, albino, though they have genes for chlorophyll. The corn plants that are homozygous for a particular gene when exposed to sunlight turn bright red (sun-red). People of certain genotypes develop face frecking when exposed to the sun.

3. Food: Genetically different organisms, even of the same species usually differ in their nutrient requirement, because of genetic mutations. They are unable to synthesize or metabolize specific compounds which must be added or removed from their diet.

4. Life Style and Physical Activity: This also contributes to gene expression. McArdle’s disease is a rare disorder in human beings. It stems from a deficiency of the enzymes phosphorylase in the muscles. Persons with this trait experience painful muscle cramps only when they engage in strenuous exercise because the absence of phosphorylase blocks the first step in glycogen degradation. Therefore, a sedentary lifestyle and avoidance of muscular stress eliminate the phenotypic expression of the trait.

5. Maternal Relations: Interactions occur between the fetus and maternal environment in mammals where the fetus leads an intrauterine life. Blood group incompatibility between mother and offspring is one example of environmental interaction.

Effects of Internal Environment:

Internal environmental effects are those phenotypic changes that are correlated to changes within the organism. These are age, sex, and the presence or absence of internal substrates.

1. Age: It has been studied, especially in human beings that the appearance of phenotypic effects of certain genes is correlated with age. Certain traits are expressed in the early life span such as the formation of blood group antigens in the fetus.

2. Sex: Sexual phenotypic differences appear because of differences in the sex chromosomes of male and female organisms. These include primary sex differences which appear during intraembryonic life and secondary sex differences that appear with sexual maturity during puberty in human beings.

3. Substrates: The activity or expression of certain genes depends on the availablity of substrate whether at the cellular or individual level. These substrates are the result of some metabolic activity within the organism.