Aligning Reads To Specific Chromosome Using Bwa

Hello Everyone,

I have whole genome illumina paired end reads and I want to align my reads to specific chromosome (chr 21) using BWA.

I was thinking of aligning the entire reads to fasta file of the human chromosome 21. Is this the appropriate way to solve my problem or is there any specific command for BWA to solve this.

Any kind of help is appreciated

Thanks Suz