Question

A recessive mutation is?
A. Not expressed
B. Rarely expressed
C. Expressed only in homozygous and hemizygous states
D. Expressed only in heterozygous state

Answer 1

Genes are the structural and functional unit of nucleic acids and these are present on the locus of the homologous chromosomes, and these genes have alleles where each gene on the chromosome have pair of alleles which represent the certain traits of the organisms.

Complete answer:
The alleles that present on the genes are of again two types, they are dominant and recessive, and based on that the phenotype is expressed.
In general the dominant alleles express their phenotypes than the recessive alleles.
As we know that each homologous chromosome has a pair of alleles and they present as either homozygous or heterozygous state, where the homozygous means the gene has both alleles which are either dominant or recessive. Whereas the heterozygous condition is that each gene has one dominant and one recessive allele, such type is called heterozygous condition.
In order to explain the recessive mutation, an example is that females have XX chromosomes, and males have XY chromosomes.
For example to inherit any X linked recessive gene, for the females they have recessive genes on both the chromosomes which means homozygous recessive, to express it.
For example in boys they have one X and one Y where they need only one recessive gene to express the condition, and this is called hemizygous condition.
So the recessive mutation can be expressed in both homozygous and hemizygous condition.
So, the correct answer is “Option C”.

Note: For the dominant one to express even one allele is enough, that is the reason in heterozygous condition only the dominant one is expressed, while the expression of recessive gene is masked by dominant one so that recessive mutations can be expressed only in homozygous or hemizygous condition.