Chromosome Types Based on Centromere Position

Chromosomes are classified based on the position of the centromere, which determines the relative lengths of the two arms (p-arm and q-arm). The centromere is a constricted region of the chromosome.

There are typically four main types of chromosomes based on centromere position:

• Metacentric: The centromere is located exactly in the middle of the chromosome, resulting in two arms of approximately equal length.
• Submetacentric: The centromere is located slightly away from the center, towards one end. This results in one arm being slightly shorter than the other (unequal arm lengths).
• Acrocentric: The centromere is located very close to one end of the chromosome. This results in one very short arm and one long arm. Acrocentric chromosomes often have satellites on the short arms.
• Telocentric: The centromere is located at the very end of the chromosome. This type is not found in humans but is present in some other organisms.

The question asks about a chromosome with a centromere located "near the middle". Let's consider the options:

• A metacentric chromosome has the centromere *exactly* in the middle.
• A submetacentric chromosome has the centromere *near* the middle, but slightly off-center, leading to unequal arm lengths.
• An acrocentric chromosome has the centromere near the *end*, not near the middle.

Based on these definitions, a chromosome with a centromere near the middle, implying it's not exactly in the middle but not close to the end either, is described as submetacentric. While "metacentric" is *in* the middle, "submetacentric" is the term used for a centromere position that is still relatively central but clearly off-center, hence "near the middle" often encompasses this type as it's closer to the middle than acrocentric or telocentric types.

Therefore, a chromosome with a centromere near the middle is called a submetacentric chromosome.