What is an allele?
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a. an organism that lives in eukaryotes
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b. a group of chromosomes
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c. a gene that causes a specific trait
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d. a chromosome that determines gender

Just did the lesson on this, the answer is  C.

Explanation:An allele is one of the possible forms of a gene. Most genes have two alleles, a dominant allele and a recessive allele. If an organism is heterozygous for that trait, or possesses one of each allele, then the dominant trait is expressed. ... So a gene is a particular region of your DNA that controls a specific trait.

stress fractures occur largely in the feet and legs and are common in sports that require repetitive impact, primarily running/jumping sports such as gymnastics or track and field.

b. to discover aspects of the natural world.

hopefully i .