Which of the following best describes an allele? (A) Different forms of the same gene. (B) All the DNA within an organism. (C) A section of DNA that codes for a protein. (D) The interaction of DNA with the environment. Or (E) similar forms of different genes.
This question is asking us to choose the answer choice that gives the best definition for the term allele. Remember, when a question asks for the best answer, there may be more than one choice that seems correct. And it’s our responsibility to choose the answer that is the most correct. So what is an allele? Within each and every one of your body’s somatic cells, you have 23 pairs of chromosomes or 46 in total. Of each of these pairs, you inherited one chromosome from your mother and one chromosome from your father. These matching pairs of chromosomes are said to be homologous.
A chromosome is a long strand of DNA. If you took the DNA from all 46 chromosomes in one of your cells and laid it out end to end, it would be over two meters long. Chromosomes are typically represented in this more compact shape they take on during cell division. Each chromosome contains many genes. A gene is a section of DNA that typically codes for a protein or controls one characteristic. Let’s imagine that at this location, we have the gene for the characteristic of eye color. In this example, this individual has inherited one allele for blue eyes trait from their mother and an allele for the brown eyes trait from their father.
In reality, eye color follows a much more complicated pattern of inheritance. But for the purposes of this example, let’s pretend that there are two options, brown and blue. You may be wondering what makes these two alleles different. The answer lies in the code, the genetic code. DNA is made of a string of nucleotides. And these nucleotides are identified by the four different bases they may possess. A for adenine, T for thymine, C for cytosine, and G for guanine. One gene may be hundreds to thousands of bases long. And the different alleles are different because the order of these bases differ between them.
The allele for blue eyes will be the same length as the allele for brown eyes because they’re two different versions of the same gene. They represent different traits within the same characteristic. Now let’s return to our answer choices. An allele is different forms of the same gene. Based on what we’ve learned, this is true. A gene represents a characteristic, like eye color, while the alleles represent different traits available within that characteristic, such as blue eyes or brown eyes.
An allele is all the DNA within an organism. This is actually the definition of genome, not allele. An allele is a section of DNA that codes for a protein. This is close, but this is the definition of a gene. An allele is more specific, one version of a gene representing one trait within a characteristic. An allele is the interaction of DNA with the environment. While the environment can certainly influence the expression of certain genes, this is not a good definition of an allele. An allele is similar forms of different genes. Again, we know that an allele represents different traits or versions within the same gene. This definition does not fit.
The choice that best describes an allele is different forms of the same gene.