Which type of chromosome may be lost during cell division?

The eukaryotic chromosomes are made up of

The part of chromosome beyond the secondary constriction is known as $:-$

Match the parts of the chromosome given in Column $I$ with their explanation in Column $II$:

Column $I$ (Chromosome)	Column $II$ (Explanation)
$1$. Centromere	$a$. Disc-shaped plate where spindle fibres get attached during cell division.
$2$. Secondary constriction	$b$. Long unbranched slender highly coiled $DNA$.
$3$. Kinetochore	$c$. Place where $2$ chromatids are joined together.
$4$. Chromatonema	$d$. Nucleolus gets organised at this place.

Choose the correct answer from the following options.

Polytene chromosomes in the salivary glands of Dipteran larvae are useful in gene mapping because they ..........

$S -$ Assertion: Individual chromosomes are not identifiable during interphase.
$R -$ Reason: They exist as highly extended and elaborate nucleoprotein fibers called chromatin.