In this chapter, we have focused on chromosomal mutations resulting from a change in number or arrangement of chromosomes. In our discussions, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. From the explanations given in the chapter, what answers would you propose to the following fundamental questions? How do we know that the extra chromosome causing Down syndrome is usually maternal in origin?

Hey everyone. Let's take a look at this question together. Down syndrome results from the trisomy of which chromosome. So we know that trisomy is when you have three copies of a chromosome instead of that normal amount of two copies. And so, looking at our answer choices, we know that the trisomy of chromosome 21 is what leads to Down syndrome. Making answer choice C the correct answer. Because we know that when we have three X chromosomes, that is something that only occurs and females three Y chromosomes is not something that is observed. And when we have three copies of chromosome 18, that is something called Edwards syndrome. And so three copies of chromosome 21 is what leads to down syndrome. I hope you found this video to be helpful. Thank you and goodbye.