Answer:
Alleles refer to the alternative form of the same gene. These are mainly of two types: dominant and recessive allele.
The dominant allele is the which mask the effect of another allele in a heterozygous condition. The allele which is masked or which is not able to express itself in a heterozygous condition is termed as a recessive allele.
For example, T (codes for tallness of a plant) is dominant over t which codes for a dwarf trait.
The organisms that contain the same allele for a particular trait is said to be homozygous for that trait. For example, TT and tt.
In contrast, if the organism contains different alleles for a particular trait, it is termed as heterozygous for that particular trait. For example, Tt.
Thus, the first, second, third and fourth blank can be correctly filled with dominant, recessive, homozygous, and heterozygous respectively.
