Question

Which statement about alleles is not true?
A. There may be several at a locus
B. One may be dominant over another
C. They may show incomplete dominance
D. They occupy different loci on the same chromosome

Answer 1

Hint:- All the genetic information of a living organism is stored in the nucleus of its cells. The nucleus contains the genetic material of an organism in the form of DNA. DNA carries all the genetic structure of an organism. It is responsible for the inheritance of the genetic characters from parents to offspring.
Genes are located on the DNA. It is responsible for inheritance.

Complete answer:-
Genes contain the data required to express a particular trait. The genes which code for a pair of contrasting traits are known as alleles. They are slightly different forms of the same gene. Thus the alternate form of a gene present at the same locus on a homologous chromosome is called alleles.
According to Mendel's law of dominance, when two different alleles are present in an individual, only one of the alleles can express itself and it is known as dominant allele whereas another allele fails to express itself and it is known as a recessive allele.
As per the law of dominance given by Mendel, F1 generation must have the dominant character. But in some organisms, the F1 generation is different from both the parents. This results in the generation of an intermediate individual thus termed as incomplete dominance.
Presence of more than two alleles of a gene at the same locus on the homologous chromosome can also be seen. These types of alleles are called multiple alleles.

Note:- Mutations can cause an allele to modify and thus the modified allele will perform a different function. Thus the phenotype will only be dependent on the function of an unmodified allele.
During incomplete dominance, both factors such as dominant and recessive are present in the formed progeny but the dominant factor is unable to express it's a character completely resulting in an intermediate type of generation that is formed which is different from both the parents.
Multiple alleles can only be studied in a population but not in an individual.