Final answer:
A chromosome with two arms of equal length is referred to as a metacentric chromosome, which is one of the several classifications based on the position of the centromere. Other types include submetacentric, acrocentric, and telocentric.
Step-by-step explanation:
When we describe the structure of chromosomes, one important aspect is the location of the centromere. The centromere is the region of a chromosome to which the microtubules of the spindle attach, via the kinetochore, during cell division. The position of the centromere determines the descriptive classification of the chromosome's shape during anaphase of cell division.
A chromosome with two arms of equal length is referred to as a metacentric chromosome. Conversely, in submetacentric chromosomes, the arms are of unequal lengths but not extremely so, resulting in one arm being slightly longer than the other. If one arm is significantly longer, the chromosome is referred to as acrocentric. Lastly, telocentric chromosomes have their centromere at the very end, essentially having no short arm.
In the karyotype, the position of the centromere, along with the number and size of the chromosomes, assists in identifying the particular chromosomes, which is valuable in diagnosing chromosomal abnormalities such as in Down syndrome, also known as trisomy 21.