An individual with Down's syndrome has repeat length alleles of size 8, 13, and
14 for a microsatellite near the centromere of chromosome 23. Her mother is homozygous for the 13 repeat allele. Her father is heterozygous for 8 and 14. What can we say about the origin of Down's syndrome in this case?
To determine the origin of Down's syndrome in this case, we need to understand the nature and inheritance of Down's syndrome. It's important to note that Down's syndrome, also known as trisomy 21, is typically caused by the presence of an extra copy of chromosome 21.
However, the information provided in your question pertains to alleles found near the centromere of chromosome 23, rather than chromosome 21. Therefore, it seems there might be some confusion.
To accurately determine the origin of Down's syndrome, you would need to analyze the chromosomes of the individual in question. This is done by karyotyping, a process involving the visualization and examination of an individual's chromosomes.
During karyotyping, the presence of an extra copy of chromosome 21 would indicate Down's syndrome originated from the individual themselves. In other words, if the individual has three copies of chromosome 21 instead of the usual two, it would suggest that Down's syndrome is due to a nondisjunction event during the formation of the individual's eggs or sperm.
If you would like further clarification or have more specific information regarding the scenario you provided, please provide additional details so I can offer more accurate guidance.