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In this article, we will elucidate with specific examples, that phenotypic variation is due to genetic factors or environmental factors, or a combination of genetic and environmental factors.
What is Variation?
When new genetic variation is inherited, it gives rise to evolution. Variation explains the differences in the genetic make-up between individuals belonging to the same species. Although the variation can exist in all cells of the body, however, it is only transferred to the next generation if it is present in gametes. In this manner, genetic variation can affect future generations and change the genetic pool of a population.
Having a large gene pool with several variations is quite advantageous because it enhances the biological fitness of the species and enables them to adapt and survive the time of selection. This die to the fact that the diversity in genetic information enables the population to be flexible to environmental changes.
In the next section of the article, we will discuss phenotype variation in detail.
Phenotype Variation
Phenotype: The phenotype of an organism refers to its observable characteristics.
Phenotype Variation: Phenotype variation refers to the difference in phenotypes between organisms belonging to the same species.
Role of Genetic and Environmental Factors in Phenotype Variation
In a few cases, genetic factors can be used to explain phenotype variation. For instance, the human population has four different blood groups. The difference in blood groups within the human population is attributed to two of three possible alleles for a single ABO gene.
In other cases, the phenotype variation is caused by environmental factors. For instance, the height of the clones of plants varies although they contain the same genetic information, i.e. DNA when they are grown under different environmental conditions.
We can also explain phenotype variation using a combination of genetic and environmental factors. For instance, a recessive allele that results in sickle cell anaemia is widely present in a population where malaria is rampant because of the heterozygous individuals being resistant to malaria.
The expression of the genotype and the interaction of the environment determine the whole phenotype of an organism. Hence, we can say that:
Genotype + Environment = Phenotype
In the next section of the article, we will explain genetic variation in detail.
Genetic Variation
Organisms belonging to the same species will have similar genotypes, However, two individuals, no matter if they are twins, will have different DNA base sequences. Regarding the size of the genomes, these differences are minute between the individuals belonging to the same species. Now, let us formally define genetic variation:
Genetic variation refers to the minute differences in base sequences of the DNA between individual organisms within a species population.
The genetic variation is passed on from one generation to the next and it results in the phenotypic variation within a species population. The processes below cause the genetic variation because they result in a new combination of alleles in a gamete or an individual:
- During metaphase I, an independent assortment of homologous chromosomes
- During prophase I, the crossing over of non-sister chromatids
- During fertilization, the random fusion of gametes
- Mutation generates new alleles
- A new allele can prove beneficial or may have a drawback or have no visible effect on the phenotype because of the degeneration of the genetic code.
- We cannot always see the new alleles in individuals when they first occur in.
- It implies that they can remain hidden within a population for many generations before they cause phenotypic variation.
Genes can have different effects on the phenotype of an organism. A single or many genes can influence the phenotype. The effect of the gene on the phenotype can be large, small, and/or additive.
In the next section of the article, we will discuss sources of genetic variation.
Sources of Genetic Variation
Let us now explain processes that cause genetic variation as discussed in the previous section, along with their mechanism and result.
Process # 1: During metaphase 1, an independent assortment of homologous chromosomes.
Mechanism: When chromosomes are randomly aligned, it causes different combinations of chromosomes and different combinations of alleles in each gamete.
Result: It results in an individual producing genetic variation between gametes.
Process # 2: During prophase 1, the crossing over of non-sister chromatids.
Mechanism: When genetic information is exchanged between non-sister chromatids, it results in new combinations of alleles on the chromosomes. Moreover, it also has the potential to break linkages between genes.
Result: It also results in an individual producing genetic variation between the gametes.
Process # 3: During fertilization, the random fusion of gametes.
Mechanism: Any male gamete can fuse with any female gamete. In other words, there is random mating in a species population.
Result: As a result of this process, genetic variation is caused between the zygotes and resulting individuals.
Process # 4: Mutation occurs which generates new alleles.
Mechanism: When the DNA base sequence alters randomly, it leads to the generation of the new allele. Mutation should exist within gametes so that it can be transferred to future generations.
Result: As a result of this process, genetic variation occurs between individuals within a species population.
In the next section of the article, we will discuss how environmental factors affect the phenotype of an organism.
Environmental Factors
Phenotype is also affected by the environment that an individual lives in. Around the world, the environments are significantly different which gives rise to different conditions in terms of:
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- Length of sunlight hours (which can be seasonal)
- Water availability
- Supply of nutrients (food)
- Levels of oxygen
- Temperature range
How an organism grows and develops depends on the changes in the above factors. For instance, plants having a tall genotype growing in an environment that has scarce minerals, water and sunlight are unable to grow to their maximum potential size influenced by genetics.
Phenotype variation that is caused only due to environmental factors or pressures is not inherited by an organism’s offspring. On the other hand, changes to the genetic component of gametes will be inherited by an organism’s offspring.
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