Question

Arm ratio in the metacentric condition is
A.1:1
B. 1:2
C. 1:3
D. 2:3

Answer 1

Each chromosome possesses two arms, labeled p (the shorter of the two) and q (the longer). These arms can be connected in either metacentric, submetacentric, acrocentric, or telocentric manner. The metacentric chromosomes are X-shaped chromosomes, with the centromere in the middle so that the two arms of the chromosomes are equal.

Complete answer: According to Levan et al. (1964), Chromosome types (CT) are-
1. Metacentric (m), with an arm ratio from 1 to 1.7
2. Submetacentric (sm), with arm ratio from 1.7 to 3
3. Subtelocentric (st), with arm ratio from 3 to 7
4. Acrocentric (a), with arm ratio more than 7
5. Telocentric (t), with only one arm.
Also, m/sm, sm/st, and st/a respectively correspond to the defined borders of the chromosome types.
A chromosome is called metacentric if its two arms are roughly equal in length. In a typical human karyotype, five chromosomes are deemed metacentric: chromosomes 1, 3, 16, 19, and 20. In some cases, a metacentric chromosome is formed by symmetrical translocation i.e by the fusion of two acrocentric chromosomes to form one metacentric chromosome. The arm ratio in the metacentric condition is 1:1 as X-shaped chromosomes have the centromere in the middle and the two arms of the chromosomes are almost equal.
So, the correct option is A- 1:1

Note: Each chromosome possesses a constriction point known as the centromere, which divides the chromosome into two sections, called the “arms.” The short arm of the chromosome is named the “p arm.” The long arm of the chromosome is named the “q arm.”