Mitochondrial DNA analysis Mitochondrial DNA (mtDNA) is used instead of nuclear DNA when forensic samples have been degraded, are damaged, or are in very small quantities. In many cases there may be human remains that are older, sometimes ancient, and the only options for DNA collection are the bone, teeth, or hair of the body. mtDNA is able to be extracted from such degraded samples because its presence in cells is much higher than nuclear DNA. There can be more than 1,000 copies of mtDNA in a cell, while there are only two copies of nuclear DNA. Nuclear DNA is inherited from both the mother and the father but mtDNA is passed down from only the mother to all of her offspring. Due to this type of inheritance, mtDNA is useful for identification purposes in forensic work but can also be used for mass disasters, missing persons cases, complex kinship, and genetic genealogy. As mentioned, the main advantage of using mtDNA is its high copy number. However, there are a few disadvantages of using mtDNA as opposed to nuclear DNA. Since mtDNA is inherited maternally and passed to each offspring, all members of the maternal familial line will share a haplotype. A haplotype "is a group of alleles in an organism that are inherited together from a single parent". The sharing of this haplotype among family members can cause an issue in forensic samples because these samples are often mixtures that contain more than one DNA contributor. Deconvolution and interpretation of mtDNA mixtures is more difficult than that of nuclear DNA and some laboratories choose not to attempt the process Since mtDNA does not recombine, the genetic markers are not as diverse as autosomal STRs are in the case of nuclear DNA. Another issue is that of heteroplasmy. Heteroplasmy is when an individual has more than one type of mtDNA in their cells. This can cause an issue in the interpretation of data from questioned forensic samples and known samples that contain mtDNA. Having adequate knowledge and understanding of heteroplasmy can help ensure successful interpretation. There are some ways to improve success of mtDNA analysis. Preventing contamination at all testing stages and using positive and negative controls is a priority. In addition, the use of mini-amplicons can be beneficial. When a sample of mtDNA is severely degraded or has been obtained from an ancient source, the use of small amplicons