Final answer:
An individual with two identical alleles for a trait is homozygous, which can be either homozygous dominant or homozygous recessive. Alleles are different versions of a gene, and the phenotype is the observable trait, while the genotype is the specific genetic makeup.
Step-by-step explanation:
If an individual has two identical alleles for the same trait, the individual is said to be homozygous for that trait. Homozygosity can come in the form of two dominant alleles, which would be referred to as homozygous dominant (e.g., AA), or as two recessive alleles, known as homozygous recessive (e.g., aa). In contrast, having one dominant and one recessive allele for a trait is termed heterozygous (e.g., Aa). Therefore, the correct answer to the student's question is option 4) homozygous.
Alleles are different versions of a gene, and an individual's genotype is the combination of alleles they possess. The phenotype is the observable trait that results from the interaction of these alleles. It is important to note that a recessive allele will affect the phenotype only when in the homozygous condition and that individuals can have the same phenotype without having the same genotype.