Importance of variation and what causes it (25)
One way in which variation is introduced is through mutations to the DNA base
sequence of individuals. Mutations arise when a base is deleted, added or
substituted for a different base within the nucleotide sequence. Equally,
translocation, inversion and duplication mutations describe what happens when
whole sections of base sequence are changed on a chromosome. Mutations increase
the genetic diversity in a population by giving rise to new alleles, therefore it would
code for a different polypeptide with a different function. Although many mutations
are maladaptive, they are important because some give their possessor a selective
advantage. For example, a mutation to the base sequence of a bacteria, such as
MRSA, can give rise to an allele coding for a protein that gives rise to resistance to
antibiotics. Exposure to treatment with antibiotics provides a selection pressure that
causes bacteria with the resistance allele to be selected for. They survive and
reproduce, passing on the allele to their offspring. Over time, the frequency of the
allele for resistance increases in the population, due to division of surviving bacteria
by binary fission, but also horizontal gene transfer. Plasmids can be replicated, then
twisted up and pulled through a tube called a conjugation pilus, allowing the genes
that they contain to be exchanged between bacteria in a population. This leads to the
rapid spread of resistance to antibiotics, which is important for the bacteria as it
allows them to survive.
A second way in which variation is introduced between individuals of the same
species is in meiosis. During prophase I, bivalents form and non-sister chromatids of
homologous chromosomes become entangled, forming chiasmata. As sections break
off, equal lengths of non-sister chromatids are exchanged in a process called
crossing over, resulting in the formation of new combinations of alleles. Homologous
chromosomes are then independently assorted (i.e. they line up at the metaphase
plate at random), which means that the combination of chromosomes of maternal
and paternal origin that end up in each daughter cell is also a matter of chance.
Finally, variation is introduced due to the fact that fertilisation is random, which
means that any male gamete can fuse with any female gamete to form the zygote.
Meiosis is important because it increases genetic variation in a population of
sexually reproducing individuals as each of the daughter cells has a unique
combination of genetic material. This is crucial for evolution as it allows for natural
selection to act on a wider range of genetic variation within a population. This, in
turn, decreases the likelihood of extinction as it is likely that some individuals will
possess an advantageous combination of alleles which give them a survival
advantage in changing environments.
A third way that variation is introduced between individuals is through epigenetics.
Epigenetics refers to a heritable change to gene function without changing the base
One way in which variation is introduced is through mutations to the DNA base
sequence of individuals. Mutations arise when a base is deleted, added or
substituted for a different base within the nucleotide sequence. Equally,
translocation, inversion and duplication mutations describe what happens when
whole sections of base sequence are changed on a chromosome. Mutations increase
the genetic diversity in a population by giving rise to new alleles, therefore it would
code for a different polypeptide with a different function. Although many mutations
are maladaptive, they are important because some give their possessor a selective
advantage. For example, a mutation to the base sequence of a bacteria, such as
MRSA, can give rise to an allele coding for a protein that gives rise to resistance to
antibiotics. Exposure to treatment with antibiotics provides a selection pressure that
causes bacteria with the resistance allele to be selected for. They survive and
reproduce, passing on the allele to their offspring. Over time, the frequency of the
allele for resistance increases in the population, due to division of surviving bacteria
by binary fission, but also horizontal gene transfer. Plasmids can be replicated, then
twisted up and pulled through a tube called a conjugation pilus, allowing the genes
that they contain to be exchanged between bacteria in a population. This leads to the
rapid spread of resistance to antibiotics, which is important for the bacteria as it
allows them to survive.
A second way in which variation is introduced between individuals of the same
species is in meiosis. During prophase I, bivalents form and non-sister chromatids of
homologous chromosomes become entangled, forming chiasmata. As sections break
off, equal lengths of non-sister chromatids are exchanged in a process called
crossing over, resulting in the formation of new combinations of alleles. Homologous
chromosomes are then independently assorted (i.e. they line up at the metaphase
plate at random), which means that the combination of chromosomes of maternal
and paternal origin that end up in each daughter cell is also a matter of chance.
Finally, variation is introduced due to the fact that fertilisation is random, which
means that any male gamete can fuse with any female gamete to form the zygote.
Meiosis is important because it increases genetic variation in a population of
sexually reproducing individuals as each of the daughter cells has a unique
combination of genetic material. This is crucial for evolution as it allows for natural
selection to act on a wider range of genetic variation within a population. This, in
turn, decreases the likelihood of extinction as it is likely that some individuals will
possess an advantageous combination of alleles which give them a survival
advantage in changing environments.
A third way that variation is introduced between individuals is through epigenetics.
Epigenetics refers to a heritable change to gene function without changing the base
