Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

What does the term homozygous refer to?

1. A genetic condition with one dominant trait

2. Two identical alleles for a trait

3. Different alleles for a trait

4. A hybrid genetic condition

The correct answer is: Two identical alleles for a trait

The term homozygous refers specifically to having two identical alleles for a particular trait. In genetics, alleles are different versions of a gene that can exist at a specific locus on a chromosome. When an organism is homozygous for a trait, it means that it has inherited the same allele from both parents, whether that allele is dominant or recessive. For example, if a trait is governed by a gene with alleles A (dominant) and a (recessive), an organism that is homozygous could have either the genotype AA or aa. This genetic condition plays a crucial role in determining the phenotype of an organism, as homozygosity can lead to the expression of a certain trait consistently across generations, depending on whether the alleles involved are dominant or recessive. In contrast, the other options refer to different genetic conditions. One option mentions a genetic condition with one dominant trait, which does not accurately define homozygosity. Another option describes different alleles for a trait, which would indicate a heterozygous condition instead. Lastly, the term hybrid is often used to describe an organism that is heterozygous for a trait, where it has one dominant and one recessive allele, further