ZOOHCC - 602: Evolutionary Biology (Theory)
Sources of variations: Heritable variations and their role in evolution
Sources of variation refer to the mechanisms that generate genetic diversity within a population. There are two main sources of variation: genetic and environmental. Genetic variation can be further divided into two categories: heritable and non-heritable.
Genetic variation and environmental variation are the two main sources of variation in populations.
Genetic variation:-
It refers to the differences in genetic makeup among individuals of the same species. This variation arises due to random mutations in the DNA sequence during replication or recombination events during sexual reproduction. These mutations create different versions of genes, known as alleles, which can affect an organism's physical or behavioral traits. Genetic variation can be passed down from parents to offspring and can accumulate over time, leading to the evolution of new species.
Environmental variation:-
It refers to the differences in the environment that can affect an organism's phenotype, or observable traits. This variation can arise from differences in factors such as temperature, humidity, availability of resources, and exposure to toxins or pathogens. Environmental variation can also interact with genetic variation to produce complex traits, such as height or weight, that are influenced by both genetic and environmental factors.
Both genetic and environmental variation can influence an organism's phenotype and behavior. For example, a genetic variation that causes a bird to have a longer beak may allow it to better access nectar from flowers, but this advantage may only be realized if the bird lives in an environment where flowers with deep nectar tubes are abundant. Similarly, an environmental variation such as exposure to a pathogen may affect an organism's ability to survive and reproduce, but this effect may be modified by the organism's genetic makeup.
Non-heritable variations:-
Non-heritable variations, also known as non-genetic variations, are differences in traits among individuals that are not caused by differences in their DNA sequence. These variations can be caused by factors such as differences in the environment, experiences, and chance events.
Non-heritable variations can also be caused by chance events that occur during development. For example, during embryonic development, random errors in cell division or environmental factors such as exposure to toxins can cause variations in traits such as eye color, height, or intelligence.
Non-heritable variations are not passed down from parents to offspring, and therefore, they do not contribute to the genetic diversity of a population. However, they can still play an important role in shaping an individual's phenotype and behavior and can have important implications for health and disease.
Heritable variations:-
Heritable variations are those that are passed down from parent to offspring through the genetic material (DNA). This type of variation is the result of random mutations that occur in the DNA sequence during DNA replication. These mutations can lead to different versions of genes, known as alleles, that can affect an organism's physical or behavioral traits.
Heritable variations play a crucial role in evolution because they are the raw material upon which natural selection acts. Natural selection is the process by which organisms that are better adapted to their environment are more likely to survive and reproduce, passing on their advantageous traits to their offspring. Over time, this process can lead to the evolution of new species.
Some examples of heritable variations include variations in eye color, height, skin pigmentation, and susceptibility to certain diseases. These variations can be advantageous, disadvantageous, or neutral, depending on the environment in which the organism lives.
Heritable variations are a key driver of evolution, providing the genetic diversity that allows organisms to adapt to changing environments over time.
Role in evolution:-
Heritable variations arise from random mutations in the DNA sequence during replication or recombination events during sexual reproduction. These mutations create different versions of genes, known as alleles, which can affect an organism's physical or behavioral traits. If a particular allele confers an advantage in a given environment, individuals with that allele are more likely to survive and reproduce, passing their advantageous allele to their offspring. Over time, this can result in an increase in the frequency of the advantageous allele within the population.
Heritable variations can also contribute to genetic diversity within a population, which is important for the long-term survival and adaptability of a species. A diverse gene pool allows a population to respond to changing environments or new selective pressures, which can be important for avoiding extinction.
Heritable variations play a crucial role in the process of evolution by providing the genetic diversity and variability that allows populations to adapt and evolve over time. Without heritable variations, natural selection would have no raw material to act upon, and evolution would not be possible.
