TheX ChromosomeShowsLessGenetic Variation atRestriction Sites ThantheAutosomes

SUMMARY Using astandard technique, 122single-copy probes werescreened for their ability todetect restriction fragment length polymorphisms (RFLPs) inthehumangenome.Theuseofastandardized RFLP screening enables theintroduction ofstatistical methods intheanalysisofdifferences inRFLPcontent between chromosomes andenzymes. RFLPsweredetected frompanels containing atleast 17unrelated chromosomes, digested withTaql, MspI, BgII, HindIll, EcoRI, andPstI. Forty autosomal probes, representing asample of2,710 base pairs (bp)perhaploid genome,weretested, and24RFLPswere found. With82X-chromosomal probes, 17RFLPswerefound in6,228 bpperhaploid genome. Thefrequency ofX-chromosomal RFLPsis three times less thanthatoftheautosomes; this difference ishighly significant (P= < .001). Thefrequency ofRFLPsrevealed byvarious restriction enzymesandthepossibility thattheX chromosome isa "lowmutation" niche inthehumangenomearediscussed.