The Hardy-Weinberg law equation theorem is the fundamental law of population genetics.it provides the basis for studying the mendelian population. this law was independently developed by GH Hardy, an English mathematical and G Weinberg, a German physician in 1908.' the Hardy-Weinberg law state that the gene and genetic frequency in Mendalin population remain constant generation after generation if there is no selection, mutation, migration or random genetic drift.'
Thus, the original proportions of the genotype in a population will remain constant from generation in a population will remain constant from generation to generation, as long as the following assumptions are met
* The population size is very large.
* Random mating occurs.
* No mutation takes place.
* No gene is input from other sources, i.e. no immigration take place
* No selection occurs.
Hardy-Weinberg principle gives the generation a tool to determine whether the evolution is occurring or not. population geneticists use the Hardy-Weinberg principle to calculate allele frequency at a starting point and then compare it with the frequencies measured at some feature time. Mathematically, it can be interpreted as a binomial expression p2 + 2pq +q2 to calculate the genotypic and allele frequencies of a population where,
p2 = % homozygous dominant individuals
p = frequency of dominant allele
q2 = % homozygous recessive individuals
q = frequency of recessive allele
2pq = % heterozygous individuals
Realize that (p + q )2 = 1 ( there are only two allele )
p2 + 2pq + q2 = 1 (there are the only genotype)
Hardy-Weinberg principle says that the sum total of all the allelic frequencies of a gene is 1. Any disturbance in Hardy-Weinberg equilibrium, i.e. change in frequency of alleles would be interpreted as resulting in evolution.
Example: An investigator has determined by the inspection that 16% of a human population has a recessive trait. Using this information, we can calculate all the genotype and allele frequencies for the population, provide the condition for Hardy-Weinberg equilibrium are met.
Given: q2 =16%= 0.4= frequency of recessive allele
2pq= 2 (0.6) (0.4) = 0.48 =48% are heterozygous individual
p2+ 2pq+ q2 = 1.00-0.52=0.48
note: Though many other factors can alter frequencies, the above five can alter the proportions of homozygotes and heterozygotes predicted by hardy-Weinberg principle.
only selection produce adaptive evolution changs because only in selection, the result depent on the nature of the envirnment. mutaion, gene flow, genetic drift, etc., operate relatively independent of the envirnment. so. the chang they produce are not shaped by the envirnment demands.
2 POLYMORPHISM
It is defined as the existence of two or more from or phenotypes of the species within the same population. Polymorphism can apply to biochemical, morphological, and behavioral characteristics. it also plays a significant role in the process of natural selection.
Polymorphism in a population may develop due to the following reasons
* Changes in the environment.
* Superiority of heterozygotes.
* mutation pressure, which may introduce a variety of alleles.
* frequency-dependent selection.
polymorphism is of following two types
TRANSIENT POLYMORPHISM
This arises when the difference from or morphs, exist in a population undergoing a strong selection pressure. The frequency of the intensity of the selection pressure, such as the melanic and the non-melanic forms of the peppered month. the distribution of insular, i.e. an intermediate variation of the peppered moth. Transient polymorphism usually applies in the following situation polymorphism usually applies the following situation
(1) When one form is gradually being replaced by another.
(2) A newly arose mutation is found to be advantageous and is favored by selection. it spread through the population and become more abundant, while the population wild type is becoming rare due to negative selection.
(3) In a changing environment, a previously rare form may become advantageous and is favored by selection. it spread throughout the population.
BALANCE (STABLE) POLYMORPHISM
This occurs when different forms coexist in the same population in a stable environment. Like the existence of the two sexes in animals and plants. These genotypic frequencies of the various polymorphism forms exhibit equilibrium since each form has a selective advantage of equal intensity. some example is
(1) ABO blood groups
in humans, the existence of the a, b, ab, o, blood group of an example of balanced polymorphism. however, the genotypic frequencies within a different population may vary, they remain constant from generation to generation within that population. This is because none of them have a selection advantage over the other. statistics reveal that the white men of blood group o have a greater life expectancy than those of other blood groups. However, interestingly they also have an increased risk of developing duodenal ulcers, which may perforation and lead to death.
(2) sickle- cell anemia in some regions of the world (e.g. part of Africa) where malaria is caused by plasmodium falciparum, natural selection favors heterogonous allelic people over both homozygotes.
(3) Tay-Sachs disease
it is common in children of Jewish heritage because one out of 40 Jewish heritage person is a heterozygote, where is one out of 380 non-Jewish people is a heterozygous carrier. this is because the grandchildren of a person suffering from Tay-Sachs disease were resistant to pulmonary tuberculosis in Bethesda Maryland. The incidence of Jewish tuberculosis patients from Eastern Europe is relatively high. This finding indicates that heterozygous carriers of Tay-such disease are resistant to pulmonary tuberculosis.
other examples: red-green color blindness in humans, the existence of workers, drones, and queen in social pin eyed and thrum-eyed from in primrose, etc.
