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what is mutation? / what is gene flow? / what is non-random mating? define - science info
It is a sudden and heritable change in an organism. It is generally due to a change in the base sequence of nucleic acid in the genome of an organism. Mutations are considered to be the ultimate source of variation. The mutation may produce a new allele that was not present earlier in the population.
It can also change the frequency of existing alleles. Virtually, any characteristic of an organism can be changed by mutation. However, some mutation is selectable (i.e. conferring them), while others are on-selectable. A selectable mutation confers a clear advantage of the mutant strain under certain environmental conditions. So, the progeny of the mutation cell is able to outgrow and replace the parent cells.
REPLICA PLATE EXPERIMENT TO DEMONSTRATE MUTATION
The adaptive significance of mutation was demonstrated by Joshua Lederberg and Esther Lederberg (1952) by replica plant experiments. in the experiment, the genetic basis of drug-resistant mutation in the bacteria Escherichia coli was tested.
from a culture of Escherichia coli derived from a single cell, they spread cell onto a 'master agar plate' each cell gives rise to a distant colony.
They place a velvet cloth onto a wooden block and pressed it gently on the master plate. As a result plate of master agar plate was made. then later touched this replica plate to a new plate containing a medium with antibiotic penicillin.
As a result of this most colonies found on the master, plate died due to penicillin. forever, a few colonies appeared on the replica plate. They were penicillin-resistant. Later, all the colonies on the master plate were tested for penicillin resistance, only those colonies that had been the source of penicillin resistance cell on the replica plate display resistance.
This given experiment indicated that some bacterial cells had acquired drug-resistant mutation even before they were exposed to penicillin. Natural selection has selected and supported the progeny carrying the beneficial mutation.
RECOMBINATION
The non-parental arrangement of alleles in the progeny is called recombination. It can result from the independent assortment and crossing over. recombination can occur not only between genes but also within genes resulting in the formation of new alleles in a population.
GENE FLOW
It is the physical movement of alleles into and out of a population. it can be a powerful agent variation because the members of two different populations may exchange genetic material.
some time gene flow is obvious when an animal moves from one place to another. if the characteristics of newly arrived animals differ from those of the animals already there, and if the newcomer is adapted well enough to the new area to survive. Gene flow also keeps separated populations genetically similar.
NON-RANDOM MATING
in this process, the organisms are mate with each other randomly this phenomenon is known as non-random mating. inbreeding (mating with relatives) is a type of non-random mating that caused the frequencies of particular genotypes to differ greatly from those predicted by the Hardy-Weinberg equilibrium.
Inbreeding does not change the frequency of the alleles, but rather increase the proportion of homozygous individuals. However, the relatives are likely to be genetically similar and thus, produce offspring with two copies of the same allele.
The population of the self-fertilizing plants consists primarily of homozygous individuals, whereas outcrossing plants, (which interbreed with individuals different from themselves) have a higher proportion of heterozygous individuals.
By increase homozygosity in a population, inbreeding tends to increase the expression of recessive alleles. Due to this marriages between close relatives are discouraged and to the same degree outlawed.
Inbreeding may also increase the possibility of producing children homozygous for an allele associated with one or more receives genetics disorders.
RANDOM GENETIC DRIFT
It was discovered by American geneticist Sewall Wright. Hence, also called Sewall wright effects. in a small population, frequencies of particular alleles may change drastically by change alone. such changes in alleles frequencies occur randomly as if the frequencies are drifting. This is known as genetic drift. it is usually rare in the case of a large population. Thus, a population must be large to be in Hardy-Weinberg equilibrium.
Genetic Drift is known to occur when by changes only certain members of the population reproduce and pass on their genes to the next generation.
Genetic drift fixes new alleles, genes that arise by mutation from time to time, and eliminates the original gene, thereby changing the genetic make of a small population.
