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If an organism is heterozygous, what does it have?

  1. Genes arranged in pairs on chromosomes

  2. Identical alleles for a trait

  3. Different alleles for a trait

  4. Mutant alleles that affect phenotype

The correct answer is: Different alleles for a trait

If an organism is heterozygous, it has two different alleles for a particular trait. This means that each parent has contributed a different version of the gene, resulting in genetic diversity. Option A is incorrect as genes are always arranged in pairs on chromosomes, regardless of whether an organism is heterozygous or not. Option B is incorrect as heterozygous organisms have different alleles, not identical ones. Option D is incorrect as not all heterozygous organisms exhibit mutant alleles.