Complex sentence: Whilst popular and advantageous, caution is required when interpreting data from mtDNa, and especially Y-DNA; as they carry only 1/4 of the effective population size compared to that of autosomal DNA (aDNA).
Split into simpler sentences: Whilst popular and advantageous, caution is required when interpreting data from mtDNa and Y-DNA. Their effective population size is only one quarter to that of autosomal DNA (aDNA).