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.