Science word of the day: AllelePronunciation: Ah-LEEL'What it means: Genes contain the instructions for the various proteins that determine traits, such as eye color or blood type. An allele is a specific variant of a gene. Alleles come in pairs, one from each parent. Some are dominant, meaning that copy will override any instruction from the other allele in the pair, and some are recessive, meaning there have to be two copies of that particular allele for those instructions to translate into an observable feature. Of course, not all inheritance is as simple as dominant and recessive patterns, particularly for traits that arise from combinations of hundreds of genes. How to use it in a sentence: We learned in grade school that alleles for brown eyes are dominant over alleles for blue eyes, leaving the kids with hazel eyes feeling lost and confused. Can you crack our science word of the day puzzle, Chain Word?