What does the law of segregation state regarding gene alleles?

The law of segregation, first formulated by Gregor Mendel, states that during the formation of gametes (egg and sperm), the two alleles for a gene segregate from each other so that each gamete carries only one allele for each gene. This principle is foundational in understanding hereditary genetics, as it explains how traits are passed from parents to offspring.

In essence, when an organism reproduces, the alleles of its genes do not stay paired but instead separate, ensuring that offspring receive one allele from each parent. This process occurs during meiosis, the type of cell division that produces gametes, where homologous chromosomes are separated into different cells, resulting in gametes that contain a single allele for each gene.

By contrast, the other options do not accurately reflect the law of segregation. The idea that alleles combine to form a solid phenotype misrepresents the concept, as the law focuses on separation rather than combination. The notion that alleles remain paired throughout an organism's lifetime contradicts the principle of segregation that underlies genetic diversity. Likewise, while environmental factors can influence the expression of genes (phenotypes), they do not pertain to the fundamental mechanics of allele segregation during gamete formation as indicated by this law.