A friend who works in a research lab performed a GWAS and discovered a tight association between a SNP allele and the disease she is studying. She concluded that the SNP allele must be the mutation that causes the disease. Explain why she is likely to be wrong.

Video transcript

Hi, everyone. Let's look at our next problem. It says the most common STRS in the human genome are blank. Let's recall from our content video. What STRS are, these are short tandem repeats. Um We can think of it as a genetic stutter for lack of a better word. Uh Imagine we have a DNA sequence in our genome here. And now let's imagine we have inserted in the sequence, a mutation that involves two repeated nucleotides. In this case, the nuclei G and T repeated five times inserted into that DNA sequence that we had. Well, that sequence of repeating GT units is an tr in this case, two nucleotides repeated five different times because they have a high mutation rate and many polymorphisms. These are useful for genealogy and genetic identification. Um They can help you trace uh relatives and distinguish different people from others uh useful for looking at relatedness in recent times. Um This is as distinguished from SNP S single nucleotide polymorphisms and that would be as you can guess from the word single, a single base permutation that occurs in over 1% of the population. These are used to look at uh in genealogy, but more looking back in farther into the past, um, and in determining halo groups. So if you're looking for um, distant ancestry, you'd look at SNP S if you're looking for uh close relatives in recent times, STRS are more commonly used for that. So our question says, which are the most common STRS? Well, these STRS can come in different uh little repeated units. So the one example we showed was a dinucleotide repeat, two bases over and over again. But when we look at our answer choices, we have choice, a dinucleotide repeat choice B trinucleotide, choice C te trinucleotide or choice D hext ti. So two repeats, three repeats, four repeats or six repeats. Looking at our refix is here uh try for three he tetra for four XF for six. Well, the most common STRS are actually the example that I gave. So dinucleotide repeats are the most common in the human genome. And in fact, a GT repeat and times is the most common STR. So that's what an STR is. And it is most common in the choice. A dinucleotide repeats. See you in the next video.