In sickle-cell anemia,what is the sequence of the defective nitrogen base on the $DNA$ strand that does not act as a template?

What does $Y$ represent in the given figure?

Define/Explain the following:
$1.$ Nucleotide
$2.$ Central Dogma

Match the following columns:

Column-$I$	Column-$II$
$(a)$ Exon	$(I)$ Non-coding sequence
$(b)$ Intron	$(II)$ Coding sequence
$(c)$ Genetic code	$(III)$ Nucleosome
$(d)$ $DNA$ packaging	$(IV)$ Nirenberg,Khorana and Matthaei

Select the correct match for $X$ and $Y$:

Column $X$	Column $Y$
$(1)$ $DNA$	$(P)$ Most abundant
$(2)$ $m-RNA$	$(Q)$ Various types based on anticodons
$(3)$ $t-RNA$	$(R)$ Carries information as genetic code
$(4)$ $r-RNA$	$(S)$ $A$ specific part acts as a template

Consider the following four statements $(a-d)$ and select the option which includes all the correct ones only $:-$
$(a)$ Transcription and translation can be coupled in bacteria.
$(b)$ The split gene arrangements represent the advanced feature of the genome.
$(c)$ The process of splicing represents the dominance of $\text{RNA-}$world.
$(d)$ The presence of introns in split gene is reminiscent of antiquity.