Environmental Effects on Phenotype Basics
This portion of the AP Biology curriculum examines the many ways in which the environment may influence an organism’s phenotypic. We’ll start by discussing what environmental variety is and how it might affect an organism. Then we’ll look at how certain environmental variables serve a definite function, while others are just accidental interactions between the environment and various characteristics of an organism that result in a phenotypic change that can be measured.
We’ll observe a characteristic of phenotypic plasticity that has evolved particularly to promote the fitness of an organism: the seasonal change of coat colour in snowshoe hares, after we look at an example of how soil pH may affect the colour of Hydrangea flowers. These alterations are epigenetic in nature since they are the consequence of differential gene expression in response to environmental stimuli. Finally, we’ll look at a few features that are affected by environmental factors, such as melanin formation in reaction to UV radiation and temperature-dependent sex determination in reptiles!
Environmental Effects on Phenotype Overview
Pea plants, like many other kinds of plants, contain genes that influence how tall they grow. Plants, on the other hand, need water to thrive. You may be able to tell the variation between a plant with a tall allele and a plant with a short allele in plants that receive water. Plants that don’t receive enough water will inevitably be stunted and develop considerably less than they might if they had access to water. This is only one example of how the environment may alter an organism’s phenotypic.
Environmental impacts on variation account for a significant amount of the variation found in most characteristics. Some environmental factors just modify the phenotype without affecting the genotype, whereas others truly impact the way DNA is expressed. These ideas will almost certainly be on the AP Exam. So stick with us while we dissect the complicated influences of the environment on many phenotypes.
Let’s begin by examining how the environment influences an organism’s phenotypic. Environmental influences on phenotypes are common knowledge in many circumstances. We know, for example, that humans come in a variety of forms and sizes. To begin, consider how a basic environmental variable such as food might influence a person’s height and weight. We all know that someone who has a lot of food and eats too much will gain weight. In comparison, someone who does not eat enough will become gaunt. As a result, it is apparent that diet influences body type phenotype.
Did you realise, however, that high-quality nutrition may also alter a person’s height? Animals (including humans) need high-quality food to reach their full potential, just as plants require water to reach their full potential. Food production and availability, according to experts, is one of the reasons why people’s average height has risen over the previous 100 years. We do know, however, that distinct populations of people grow and shrink at different rates and at different periods.
So, how can scientists tell how much of a characteristic is influenced by the environment and how much is influenced by genetics? Scientists begin by calculating the following equation:
Genetic Variation + Environmental Variation = Total Variation
VE + VG = V
Knowing that these two components make up total variation, we may deduce that total variation minus environmental variation equals genetic variation.
VG = V – VE
This equation tells us how much variance is caused by the environment and how much is caused by genetics. To begin with, we must conduct experiments to determine the level of environmental variation. Consider doing an experiment to see how water affects the height of cloned plants. One batch of clones is given as much water as they can stand.
We give the other clones just enough water to keep them alive. At the conclusion of the trial, we can measure the difference in height between these two groups. Because these plants are clones, their genes are identical. This suggests that this level of diversity is solely attributable to environmental factors rather than hereditary factors.
Then we may go out and test the variance in a natural collection of plants in places with varying water levels. We can compute the genetic variation and the contribution of both environmental and genetic variability to overall variability if we know the total variance and the environmental variation.
The topic of “why does the environment influence phenotype?” is a difficult one to answer. Consider the following scenario: The Hydrangea plant produces blooms in a variety of colours, ranging from pink to dark blue. Only one of these variants, the white hydrangea, is the product of a faulty gene. White hydrangeas don’t create any colour molecules at all, but the other three kinds do.
Surprisingly, aluminium ions in the soil cause this pigment molecule to react. The pH of the soil influences the availability of aluminium ions in the leaves. Aluminum ions are readily absorbed by plants when the soil pH is acidic. Within the pigment molecule, these aluminium atoms trigger a chemical process that causes each pigment molecule to reflect blue light.
When the same plant is moved to a more basic soil, aluminium bonds to hydroxide ions in the soil and is unable to be carried into the plant. As a result, the pigment molecule is never changed and stays red. A small quantity of aluminium is present in the plant at a neutral soil pH, and part of the pigment is changed, resulting in the purple colouring.
So, although scientists have found a solution to the immediate issue of why the environment affects phenotypes, they still don’t know what the ultimate goal of this shift is in the plant. There is currently no evolutionary benefit to having a flower that functions as a pH test.
However, as we’ll see in a few moments, many phenotypic alterations generated by the environment serve a clear function and improve an organism’s fitness.
Seasonal molting event
Consider the snowshoe hare for an example of planned and directed environmental diversity. The snowshoe hare, like many other animals that live in cold, snowy climates, goes through a seasonal moulting event. During the winter, the hare’s hair is pure white, but in the summer, it becomes brown. In all seasons, the hare’s two diverse colour phenotypes aid in concealment. Phenotypic plasticity is the term for this.
These modifications, unlike some of the environmental differences we’ve identified, are epigenetic. This implies that environmental cues affect which genes are expressed in particular situations. In fact, scientists have discovered over 600 genes that respond to environmental inputs by changing their expression patterns. For example, as winter gives way to spring, the rabbit is assaulted by a slew of environmental stimuli. More sunshine is available, more nutritious vegetables begin to grow, and the temperature begins to climb.
These changes in the environment activate a variety of signal transduction pathways, which in turn affect the expression of a huge number of genes. Genes involved in hair development, as well as genes involved in the creation of pigment molecules, are activated. This induces the growth of a new coat of hair, resulting in the moulting phase that occurs between the winter and summer phenotypes. It does, however, influence genes involved in metabolism as well as the release of hormones that initiate the reproductive cycle. All of these modifications eventually result in the hare phenotype we observe in the summer.
Unlike the previously documented changes in bloom colour, these environmental fluctuations have a clear evolutionary benefit: they not only keep the hare well disguised, but they also prepare the hare for changing seasons and guarantee the hare is reproducing at the proper time of year.
Few examples of Environmental Effects on Phenotype
Let’s take a look at a few additional instances of environmental diversity. Let’s begin by looking at the skin tanning procedure. UV radiation causes a phenotypic shift from lighter to darker skin, which is known as tanning. Contrary to common perception, everyone, including those with naturally dark skin, goes through the tanning process. Melanin, a pigment molecule generated by melanocytes situated many cell layers deep under your skin, is responsible for both dark and tanned skin.
Melanin goes through the skin cells to the surface, where it may protect the skin from damaging UV radiation. Melanin synthesis is actually increased by UV rays travelling through unprotected skin, which creates reactive oxygen species in the cells. These reactive oxygen species damage DNA and activate signal transduction pathways, resulting in enhanced melanin gene expression.
However, following the first sun exposure, this process takes around 10 days to completely activate. That’s why, instead of obtaining a tan right away, many individuals get sunburned on their first exposure to the sun. UV rays have caused extensive damage to your skin cells, resulting in this redness. Because tanning occurs only after UV damage, you should always use sunscreen and consider a spray-on tan to prevent the risk of skin cancer.
Temperature-dependent sex determination
Let’s have a look at another fascinating sort of environmental variation in reptiles: temperature-dependent sex determination! The X and Y chromosomes determine sex in animals. In birds, the sex of each individual is determined by a similar but opposing pair of chromosomes known as Z and W. In reptiles, on the other hand, each individual inherits an identical set of chromosomes. The chromosome will produce male hormones and the baby will be male if the egg is kept cool during incubation. The chromosomes produce female hormones when the egg is kept heated during incubation, and the offspring will be female.
This works effectively in the nest because certain portions of the nest are reasonably warm while others are chilly. Each nest produces a mixture of male and female offspring. While this temperature-dependent type of sex determination has served reptiles well for hundreds of millions of years, global warming may result in more females and fewer males, putting the existence of many diverse reptile species in jeopardy.