_____allele from that is only seen when it is homozygous
Answers
An allele (UK: /ˈæliːl/, /əˈliːl/; US: /əˈliːl/; modern formation from Greek ἄλλος állos, "other") is a variant form of a given gene, meaning it is one of two or more versions of a known mutation at the same place on a chromosome. It can also refer to different sequence variations for a several-hundred base-pair or more region of the genome that codes for a protein. Alleles can come in different extremes of size. At the lowest possible end one can be the single base choice of a single nucleotide polymorphism (SNP). At the higher end, it can be the sequence variations for the regions of the genome that code for the same protein which can be up to several thousand base-pairs long.
Sometimes, different alleles can result in different observable phenotypic traits, such as different pigmentation. A notable example of this trait of color variation is Gregor Mendel's discovery that the white and purple flower colors in pea plants were the result of "pure line" traits which could be used as a control for future experiments. However, most alleles result in little or no observable phenotypic variation.
Most multicellular organisms have two sets of chromosomes; that is, they are diploid. In this case, the chromosomes can be paired: each pair is a set of homologous chromosomes. If both alleles of a gene at the locus on the homologous chromosomes are the same, they and the organism are homozygous with respect to that gene. If the alleles are different, they and the organism are heterozygous with respect to that gene.
Recessive
Because its effect will only be seen when both the alleles are recessive in nature.
If dominant allele it's also present then recessive allele can't express it's character.