As humans, we all belong to the same species but we don't look or act the same way. These differences in how we look and behave are called phenotypic variations. In this article, we'll talk about what phenotypic variations are, what causes them, and give some examples. We'll also talk about why phenotypic variation is important in natural selection.

What is the definition of phenotypic variation?

The phenotype of an organism refers to its observable traits- its physical appearance, behavior, learning ability, mode of reproduction, and so on. Phenotypic variations are differences among organisms in these observable traits.

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What are the causes of phenotypic variation in a population?

Phenotypic variation in a population is caused by two main factors: genotypic variation and environmental influence (Fig. 2).

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Genotypic variation

Genotype refers to the genetic information of an organism, which is made up of the combination of alleles or gene variants an organism has. The genotype influences the phenotype or observable traits of an organism. An organism can be either homozygous, meaning it has two identical alleles for a particular gene, or heterozygous, meaning it has two different alleles for a particular gene (as shown in Figure 3).

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It's important to understand the difference between homozygous and heterozygous genotypes because they affect how traits are passed down from parents to their offspring. We'll discuss this further in the examples later on. Genotypic variations, or differences in genotype, contribute to the variation we see in observable or phenotypes. These variations can be caused by mutations, gene flow, and sexual reproduction:

Mutation is a change in the sequence of genes in DNA. It is the ultimate source of new alleles.

Gene flow occurs when genes are introduced from one population of organisms to another. This can happen when organisms migrate and mate with a different population or when pollen or seeds are carried to a population that's far away.

Sexual reproduction creates new combinations of genes, leading to genetic variation.

Environmental influence

Environmental factors such as climate, food availability, and interactions with other organisms can affect the development of inherited traits, leading to phenotypic variations. This ability of a genotype to produce different phenotypes in response to different environmental conditions is known as phenotypic plasticity.

For instance, differences in food availability can result in size and weight variations among organisms of the same genotype. Likewise, differences in climate, such as dry season versus wet season, can affect crop yields. In both cases, growthic are not heritable and cannot be passed on from parent to offspring.

The thermosensitivity of the embryo in some species of reptiles is another exciting example that demonstrates how environmental influence can affect the phenotype of an organism. Exposure of freshwater turtle embryos, for example, to various temperature ranges during a specific two-week period (referred to as the "thermosensitive period") in their development can affect the sex of the resulting baby turtle. Only female turtles hatch when exposed to 30°C, while only male turtles hatch at 25°C. When exposed to around 28.5°C, a mixture of male and female turtles hatch.

What are examples of phenotypic variations?

Phenotypic variations can be classified as either discrete or continuous. Examples of each type will be discussed in the following section.

Discrete variations

Discrete variations refer to traits that have distinct and separate categories with no intermediate forms. An example of this is blood type, where there are only four possible types: A, B, AB, or O.

In discrete variations, the combination of alleles at a single gene locus (the position of a gene on a chromosome) has a significant impact on the phenotype. For instance, inheritance of sickle cell anemia in humans and the stem color of tomato plants are examples of discrete phenotypic variations.

Let's take a closer look at sick cell anemia as an example. Suppose a gene determines whether or not a human has sickle cell anemia. The alleles of this gene could lead to either normal or sickle-cell hemoglobin. As discussed earlier, a genotype could be homozygous or heterozygous, resulting in the following genotypes:

• A homozygous genotype will have alleles that are either both normal or both sickle-cell. A homozygous genotype with two sickle-cell alleles will have sickle cell anemia. All their hemoglobin will have difficulty transporting oxygen. A homozygous genotype with two normal alleles will have completely normal hemoglobin.
• A heterozygous genotype will have one normal allele and one sickle-cell allele. Such an individual will have some normal hemoglobin and some sickle-cell hemoglobin. They will have a sickle-cell trait but will appear normal.

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Another example of discrete phenotypic variation in plants is the flower color of pea plants. The color of the flowers is determined by two alleles, one for purple and one for white. A pea plant that has two alleles for purple flowers will have purple flowers, while a pea plant that has two alleles for white flowers will have white flowers. A pea plant that has one allele for purple flowers and one allele for white flowers will have purple flowers, as the allele for purple flowers is dominant over the allele for white flowers.

Similarly, in humans, earlobe attachment is another example of discrete phenotypic variation. The trait is determined by two alleles, one for attached earlobes and one for unattached earlobes. A person with two alleles for unattached earlobes will have unattached earlobes, while a person with two alleles for attached earlobes will have attached earlobes. A person with one allele for attached earlobes and one allele for unattached earlobes will haveattached alleleattachedes is dominant over the allele for attached earlobes.

Continuous variations

Continuous variations refer to traits expressed as quantitative differences with a wide range values. In contrast to discrete variations, for continuous variations, the combination of alleles at a single or. Height, weight, and skin color are examples of continuous variations in humans.

Polygenes are multiple genes that have an additive effect on one trait, and traits determined by multiple genes are called polygenic traits. For instance, height is a polygenic trait that is determined by multiple genes with an additive effect.

Phenotypic variations necessary for evolution by natural selection because they lead to different survival and reproduction rates among organisms. Evolution by natural selection can take place when these differences are present. phenotypic variation, a population cannot evolve.

Inbreeding and genetic drift are factors that can lead to reduced phenotypic variation. Inbreeding reduces the number of alleles in the gene pool of the population, leading to loss of genetic variation. Genetic drift occurs when chance events cause allele frequencies to change at random, potentially causing individuals with inherited traits to die out, hence reducing genetic variation.

With less genetic variation, it becomes less likely that there are individuals with the traits needed to survive changes in environmental conditions, which can lead to the extinction of the population or the entire species. 

Phenotypic Variations - Key takeaways The phenotype of an organism refers to its observable traits. Phenotypic variations are differences among organisms in terms of these observable traits. Phenotypic variation in a population is caused by two main factors: genotypic variation and environmental influence. Genotypic variations are caused by mutations, gene flow, and sexual reproduction Environmental conditions can also influence the development of inherited traits Phenotypic variations due to environmental influence are not passed on from parent to offspring Phenotypic variations can be classified as either discrete or continuous. Discrete variations are traits with qualitative differences. Continuous variations are traits expressed as quantitative differences with a wide range of values. Without phenotypic variation, evolution by natural selection cannot take place.

Phenotypic Variations

What is phenotypic variation?

The phenotype of an organism refers to its observable traits- its physical appearance, behavior, learning ability, mode of reproduction, and so on. Phenotypic variations are differences among organisms in these observable traits.

What factors cause phenotypic variation?

Phenotypic variation in a population is caused by two main factors: genotypic variation and environmental influence. 

What process produces many variations in phenotypes?

Differences in genotype (or genotypic variations) produce phenotypic variation. Genotypic variations are caused by mutations, gene flow, and sexual reproduction. Environmental conditions such as climate, availability of food, and interactions with other organisms can contribute to phenotypic variation. 

Why is phenotypic variation necessary for natural selection?

Phenotypic variations lead to different survival and reproduction rates among organisms. Natural selection--where individuals with traits that are more adapted to the environment have more chances of survival and reproduction--can only take place when these differences are present.

What are the possible causes of phenotypic variations?

Phenotypic variation in a population is caused by two main factors: genotypic variation and environmental influence.

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