If a line having the chromosome pair of one species is replaced by pair of chromosome from another species is known as

If a line having the chromosome pair of one species is replaced by pair of chromosomes from another species is known as the Alien substitution line.
Alien Substitution takes place when chromosome(s) of another species replace the own chromosome(s) of a species. Alien substitutions may be obtained from alien addition lines.
Chromosome segment substitution lines (CSSLs) are genetic stocks representing the complete genome of any genotype in the background of a cultivar as overlapping segments.