Advantages and Limitations of Y-STR DNA Analysis of Semen   Samples from Rape Kits

Biological Aspects of Forensic Science
Professor Eric N. Bernard, MFS, MT (ASCP)
Tuesday 8:00PM-10PM

Jennifer Daniels-Higginbotham

Advantages and Limitations of Y-STR DNA Analysis of Semen   Samples from Rape Kits

I. Y-STR DNA Analysis
      A. Methods
1. Y-STR markers
      B. Uses of Y-STR Markers
          1. Majority of cases
          2. Minority of cases
II. Advantages of Y-STR
      A.   Advantages
          1. Mixed genotypes
          2.   Azoospermic males
          3. Commercial Kits
III. Limitations of Y-STR
      A. Expense
      B. Low discrimination power
      C. Related individuals
      D. Loci are not Independent
IV. Conclusion
A. Advances in Y-STR Typing


Short tandem repeat (STR) analysis is widely used in identifying the origin of biological fluids in the investigation of sexual assault crimes. Difficulties in the analysis of these fluids have arisen due to specimens that result in mixed genotypes. Mixed genotypes are a result of the assailant’s sperm not being completely separated from the victim’s epithelial cells making genotype analysis challenging. Difficulties have also transpired when the presence of spermatozoa is minimal or absent. The absence of spermatozoa can be due to many factors, including a condition called azoospermia. Azoospermia is a medical condition where a male does not have a measurable level of sperm in his semen, resulting from a vasectomy or other medical condition. Since a majority of the DNA in the ejaculate comes from Spermatozoa, azoospermic individuals leave less DNA to be analyzed. Scientist continue to look for new and improve current differential extraction methods to improve DNA analysis of rape kits. The use of Y-STRs (DYS19, DYS38I, DYS389II, DYS390, DYS391, DYS392 and DYS393) in DNA analysis of seminal fluid samples in azoospeermic assailants has many...