What is the difference between a gene and a allele?

A gene is a portion of DNA that determines a trait. A trait is a characteristic, or a feature, passed from one generation to another, like height or eye color.

Explanation:

"Genes come in multiple forms, or versions. Each of these forms is called an allele. For example, the gene responsible for the hair color trait has many alleles: an allele for brown hair, an allele for blonde hair, an allele for red hair, and so on."

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation:

the electromagnetic energy from the sun arrives in the form of visible and invisible light.