Question

Answer the following by using the term which is used for describing a chromosome having a centromere at its middle.

Answer 1

Centromere essentially means a constriction present on the chromosome. It is also known as primary constriction. The chromonemata , the filamental appearance of chromosome material or the arms of the chromosomes are connected at centromere. The term chromonemata was coined by Vejdovsky.

Complete answer:
Chromosomes are the condensed form of chromatin material present in the nucleus of the cell which are formed during cell division; the term chromosome was coined by Waldeyer. Mitotic metaphase stage of the cell division is most favourable for measurement of size of chromosome and is between 3 to 12 microns in various organisms. Chromatid is the longitudinal half of chromosomes containing DNA molecules. In metaphase, two chromatids are present which are attached to centromeres.
Chromosomes are classified into various types based on various parameters.
a.) Function of chromosomes
b.) Number of centromeres
c.) Position of centromeres.
Chromosomes divided on basis of number of centromeres are:
Autosomes: Chromosomes not involved in sex determination, responsible for vegetative characcters.
Allosomes: Involved in sex determination and sexual characters .
Chromosomes divided on basis of number of centromeres are:

1. Monocentric: Presence of only one centromere, most common.
2. Dicentric: Presence of two centromeres
   Polycentric: Presence of many centromeres.
   Monocentric chromosomes are divided based on position of centromere are:
   1.) Telocentric: Single armed chromosomes having centromere located at the one end of chromosome. Appear as ‘I’ or Rod shaped chromosomes during anaphase.
   2.) Acrocentric: They appear with two unequal arms, centromere is located at close to one end of chromosome forming ‘j’ shape during anaphase.
   3.) Sub-metacentric: They also form unequal arms with centromere located slightly away from the center of chromosome. They appear as an ‘L’ shape during anaphases.
   4.) Metacentric :The centromere of the chromosome is located at the center, forming two equal arms appearing as ‘V’ shape during anaphase.

Hence the answer is the term ‘Metacentric’ used for describing a chromosome having centromere at middle.

Note:
Chromosomes are the physical basis of heredity. The number varies largely in number from species to species. Example, in humans, two sets of chromosomes of which 22 pairs are autosomes and 1 pair is autosome. Number of Metacentric chromosomes in humans are five, which are labelled as 1, 3,16, 19 and 20.