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miniPCR bio™ Electrophoresis Forensics Lab. Wrongfully Convicted? Instructor's and Student's Guide Version: 1.1 - Release February 2022 - © 2022 by miniPCR bio™ Student's Guide P./10 Non-coding regions of the genome When we think of DNA, we often think of genes, which contain the coded instructions to make RNA and proteins. However, the majority of the genome doesn't code for proteins. Scientists refer to this DNA as non-coding DNA. Non-coding DNA can have many functions. For example, non- coding DNA can be involved in gene regulation or have a structural role, like protecting the ends of chromosomes. There are also many regions of non-coding DNA where scientists don't know what the function is, or if it even has a function. Importantly, these non-coding regions are more variable between individuals than coding regions. For this reason, forensic scientists analyze non- coding regions of the genome when creating DNA profiles. An allele is one of two or more versions of a DNA sequence that appears in the same location in the genome. Forensic scientists refer to STR alleles by the number of tandem repeats they contain. In the example of STR 1, if there are 5 GATA repeats, then forensic scientists would say that it is the "5" allele. Because humans have two copies of each chromosome, one inherited from each biological parent, people have two alleles for each STR region. Scientists use the term genotype to refer to different combinations of alleles that a person could have. For instance, someone who is "9, 9" at STR 1 inherited 9 GATA repeats from each parent. On the other hand, someone who is "5, 9" at STR 1 inherited 5 GATA repeats from one parent and 9 GATA repeats from their other parent (Figure 2). Maternal chromosome STR 1 Paternal chromosome STR 1 genotype: 9, 9 STR 1 ......AACTAAC GATA GATA GATA GATA GATA GATA GATA GATA GATA GACAGAT...... 9 REPEATS 9 REPEATS Person A Maternal chromosome STR 1 Paternal chromosome STR 1 genotype: 5, 9 STR 1 ......AACTAAC GATA GATA GATA GATA GATA GACAGAT...... ......AACTAAC GATA GATA GATA GATA GATA GATA GATA GATA GATA GACAGAT...... 5 REPEATS 9 REPEATS Person B ......AACTAAC GATA GATA GATA GATA GATA GATA GATA GATA GATA GACAGAT...... Figure 2. STR genotypes People have two alleles for each STR region in the genome. The alleles could be the same or they could be different. Person A has two copies of the same allele for STR 1 and their genotype is 9, 9. Person B has two different alleles for STR 1 and their genotype is 5, 9.