L-shaped chromosomes are called as (a)Sex chromosomes (b)Acrocentric (c)Telocentric (d)Sub-metacentric
Hint: During metaphase, chromosomes are stretched as they are separated due to the forces exerted by the spindle fibres. While being dragged towards the daughter nucleus, various chromosomes appear to have different shapes.
Complete answer: The chromosome is divided into two sections or ‘arms' at a constriction point known as the centromere. The centromere is the position of DNA that acts as a link between the two sister chromatids. The characteristic shape of the chromosome is given by the position of the centromere on each chromosome. If the centromere is present slightly near the centre, the chromosome arms appear unequal and hence look like the shape of the alphabet ‘L’ during metaphase.
Additional Information: On the basis of how the chromosomes appear at the metaphase of cell division, chromosomes are divided into 4 main types. Out of which sub-metacentric is as explained above. The remaining three types are - Metacentric: The centromere is present almost exactly at the centre. The two arms seem almost of the same length. We can also say that the centromere is located in the middle of the complete structure. These chromosomes appear in the shape of alphabet ‘V’ during metaphase. Acrocentric: The centromere is seen almost towards the end region. The term “acro” in Greek relates to “peak”. Thus, the name acrocentric refers to the type where the centromere is near the terminal region. These chromosomes appear in the shape of the alphabet ‘J’ during metaphase. Telocentric: The centromere is present at the extreme end. That is the centromere is present in the telomeric region. Hence the name telocentric. However, these telocentric chromosomes are not found in humans. These chromosomes appear in the shape of the alphabet ‘i’ during metaphase. So, the correct answer is Sub-metacentric i.e option (d).
Note: Some chromosomes also have secondary constriction. These chromosomes are called SAT -chromosomes or marker chromosomes. Some of these secondary constrictions are involved in the formation of nucleoli.