Question

A long answer question will require one to three paragraphs

Describe and compare the phenomena of genes that follow polygenic inheritance, multiple alleles, codominance, and incomplete dominance?

Answer 1

Polygenic inheritance

It is also known as multiple gene inheritance.It ocurs when one characteristics is controlled by two or more genes.Genes will be large in quantity but small in effect.Main mode of nonallelic gene interaction in gene series is through addition of small allelic contibutions.Polygenic characters show a continous distribution rather than discontinous distribution.The phenotypic effects of the polygenic characters is undergoing considerable modification by environmental influence.The effects of allelic substitution at each of the segregating genes are relatively small and interchangeable.when the frequencies of the phenotypic values are plotted ,a bell shaped curve is obtained.The mode of distribution represents the optimal or fittest phenotype.

Multiple alleles

Multiple alleles are two or more alternative forms of a gene that can occupy the same locus.But only two of the alleles can present in an organism.It exists in a population when there are many variations of a gene present.Both haploid and diploid organisms creates new alleles by spontaneous mutations.The effect of this mutation is a different sequence of nucleic acid bases in the dna.Any one of a series or alternative or allelic forms of a gene about which two only exists.Examples are the gene of ABO blood group system and the humsn leukocyte associated antigens.

Codominance

It is a form of inheritance wherein the alleles of a gene pair in a heterozygote are fully expressed.so the phenotype of the offspring is a combination of the phenotype of the parents.Thus,the trait is neither dominant nor recessive.Two different versions of gene are expressed,and each version makes a slightly different protein.Both alleles influence the genetic trait or determines the characterstics of the genetic condition.Codominance means that neither allele can mask the expression of other allele.examples includes ABO blood group in humans,where alleles A and B are both expressed.If a person inherits an allele A from mother and allele B from father,then they have blood type AB.

Incomplete dominance

It occurs when a dominant allele ,or form of a gene does not completely mask the effects of a recessive allele.so the organisms resulting physical appearance shows a blending of both alleles.It can also be called as semi dominance or even partial dominance.in incomplete dominance the third phenotype will be something in the middle of both the dominant and recessive alleles.Two better examples of incomplete dominance are height and har color.It occurs because neither of the two allelse are fully dominant over the other.In polygenic inheritance it occurs in the traits of eye color and skin color.it is a corner stone in th study of non-mendalian genetics.