Down syndrome from the view of an 8 year old

Last night I was laying next to Travis before bed, and I shared with him that one of my graduate students has a sister with Down syndrome. He responded by saying, 'they could be friends.' I explained that her sister is an adult. He said, 'oh, I thought she was Kat's age.' Then he asked, 'how do people have babies with Down syndrome?' I replied, 'that is a something that scientists don't completely know the answer to.' But, I explained to him that he and I have 46 chromosomes and Kat has 47 chromosomes. He asked, 'what's a chromosome'...ok that's fair, he's only 8, but I forget that sometimes! I said a chromosome is a cell and that we get 23 from our mom and 23 from our dad. Then, in his infinite curiosity he asked, 'where does the extra one come from?' I replied, 'that is a GREAT question.' Again, I told him that scientists aren't entirely sure about that either, BUT they suspect it comes from the mom. His face lit up and he said, 'I was thinking the mom TOO!' It's definitely a journey helping Travis understand what Down syndrome really means, and I know that will come in time. For now, he knows Kat is somehow different, and yet on the other hand, he knows that she's simply his sister. When we were dropping him off at school yesterday I was reminded of the uniqueness of their relationship as brother and sister. I opened the car door to help him get out and he was leaning over giving Kat a kiss on the forehead. Then he asked her to give him a kiss back ;-) All that really matters is that he loves her and honors her as an individual. I'm pretty sure that part is taken care of.