11 lines (10 with data), 377 Bytes

>chrM
GATCACAGGTCTATCACCCTATTaaCCACTCACGGGAGCTCTCCATGCAT
TTGGTATTTTCGTCTGGGGGGTGTGCACGCGATAGCATTGCGAGACGCTG
>chr1 single_word_description
ACCACCATCCTCCGTGAAATCAATATCCCGCACAAGAGTGCTACTCTCCT
AAATCCCTTCTCGTCCCCATGGATGA
>chr2 multi-word description is here
CGCTNCGGGCCCATAACACTTGGGGGTAGCTAAAGTGAACTGTATCCGAC
ATCTGGTTCCTACTTCAGGGCCATAAAGCCTAAATAGCCCACACGTTCCC
CTTAAATAAGACATCACGATG