Question

The chcomoseme in which centromere lies slightly away from the middle of the chromosome resulting into one shorter arm and one longer arm, is called as 1 (a) metacentric (b) submetacentric \(\begin{array}{ll}\text { (c) acrocentric } & \text { (d) telocentric. }\end{array}\) if

Short answer

The correct option is (b) submetacentric.

Step-by-step solution

Identify the Characteristics

The key characteristic mentioned is that the centromere lies slightly away from the middle of the chromosome, resulting in one arm being shorter than the other. This hints at the classification of the chromosome based on the position of the centromere.

Match the Characteristics to the Correct Term

According to the standard definitions: metacentric chromosomes have a centromere in the middle, making arms of equal length. Submetacentric chromosomes have the centromere slightly off-center, resulting in one arm being shorter than the other. Acrocentric chromosomes have the centromere significantly off-center, but not at the very end, making one arm much shorter. Telocentric chromosomes have the centromere at the very end of the chromosome.

Choose the Correct Option

Since the chromosome described has its centromere slightly away from the middle, with one shorter arm and one longer arm, the correct classification is submetacentric, which corresponds to option (b).

Key concepts

Chromosome Classification

Chromosomes are essential components of living cells that carry genetic information in the form of DNA. Chromosome classification is mainly based on the position of the centromere, which is the point on a chromosome where the two chromatids are held together and which plays a crucial role during cell division. There are four primary types of chromosomes classified according to centromere position: metacentric, submetacentric, acrocentric, and telocentric.

Understanding the structure of different chromosome types is vital in genetics and biology because certain characteristics and behaviors during cell division vary depending on the centromere's location. This classification also aids in the study of chromosomal abnormalities and their implications in various genetic disorders.

Centromere Position

The centromere position on a chromosome has significant relevance in genetics because it influences the balance and movement of chromosomes during cell division. A chromosome's centromere can be centrally located or positioned near one of the ends. This position is often indicative of certain genetic features and can help scientists predict how chromosomes will segregate during the complex process of cell division.

There are characteristic arm ratios and shapes that result from different centromere positions. The arms of a chromosome are referred to as 'p' for the short arm and 'q' for the long arm. A balanced chromosome usually has arms of equal or nearly equal length, while an imbalance can cause a variety of arm length ratios, leading to a distinct classification.

Metacentric Chromosome

A metacentric chromosome features a centromere that is positioned in the middle, thus producing two arms of roughly equal length. Visually, it resembles the letter 'X' when the chromosome is condensed and visible under a microscope during cell division.

The equidistant position of the centromere allows the metacentric chromosome to maintain balance and structure, contributing to even distribution during mitosis and meiosis. As a result, geneticists often find metacentric chromosomes simpler to identify and map due to their symmetrical shape.

Acrocentric Chromosome

An acrocentric chromosome is characterized by a centromere that is significantly off-center, closer to one end of the chromosome. This results in one very short (almost dot-like) 'p' arm and one long 'q' arm.

Importance of Acrocentric Chromosomes

In humans, certain acrocentric chromosomes are critical because they contain genes for ribosomal RNA. However, because these chromosomes have such short 'p' arms, they also raise unique concerns regarding genetic abnormalities, such as Robertsonian translocations, which are a type of chromosomal rearrangement.

Telocentric Chromosome

A telocentric chromosome is one where the centromere is situated at the very tip of the chromosome. As such, it forms a 'T' shape during cell division and essentially possesses only one arm.

Distribution of Telocentric Chromosomes

While this type can be found in certain organisms, it is not present in humans. Studying telocentric chromosomes contributes to understanding the diversity of genetic architectures across species and their evolutionary trajectories. Moreover, the presence or absence of these chromosomes can have significant implications for the genetic makeup of organisms.