Final answer:
Alternate forms of the same gene are called alleles, which are responsible for the variety of traits observed within a species. These alleles are variations of genes located on homologous chromosomes inherited from each parent, causing individuals to be homozygous or heterozygous for a trait.
Step-by-step explanation:
Alternate forms of the same gene are called alleles. This directly answers the student's question, where the correct answer is D. alleles. Alleles are significant in the study of genetics because they account for the diversity of traits observed in biology.
In diploid organisms, chromosomes come in matched pairs known as homologous chromosomes. Homologous chromosomes are identical in length and have the same sequence of genes at the same loci. However, while the genes (functional units of chromosomes that code for specific proteins) may be the same, their versions, or alleles, can vary, leading to different expressions of traits. For example, the gene for hair color can have alleles for blonde, brown, or black hair, each coding for the production of a different amount of pigment.
The variation in alleles between the two homologous chromosomes is what creates variation in traits. One homologous chromosome is inherited from each parent, so a child may inherit different alleles for a particular gene from each parent. If both alleles are the same, the organism is homozygous for that trait; if they are different, the organism is heterozygous. This genetic variation is fundamental to the process of inheritance and the principles first outlined by Gregor Mendel, the father of modern genetics.