In monohybrid inheritance, if an organism carries two different alleles for a particular gene, it is called:

1. Analyze the question The question asks for the term used when an organism carries two different alleles for one gene.

2. Explain the concept

• An allele is one of the alternative forms of a gene.
• Every diploid organism has two alleles for each gene, one from each parent.
• The pair of alleles can be: • Identical (e.g., TT or tt), which is homozygous. • Different (e.g., Tt), which is heterozygous.

3. Solution, step by step

• The organism has two different alleles, for example Tt.
• Option A, Homozygous: this means two identical alleles (TT or tt). It does not fit.
• Option B, Dominant: this describes an allele that shows its effect even when only one copy is present. It describes an allele, not the genotype of an organism with two different alleles.
• Option C, Heterozygous: this means two different alleles (Tt). It fits.
• Option D, Recessive: this describes an allele that is only expressed when two copies are present. It does not fit.

4. Answer The correct option is C. Heterozygous.

5. Exam tip Use the Greek prefixes: homo = same, hetero = different. So "heterozygous" means "different zygote (allele) combination."

Also remember that dominant and recessive describe alleles or traits, while homozygous and heterozygous describe the genotype of the organism.