It has been alleged that Thomas Jefferson fathered children with one of his slaves, Sally Hemings. These decedents wish to recognized as blood relatives of a famous president. There has been some recent genetic analysis from Sally Hemings' male descendants. Thomas Jefferson only had one daughter that produced direct decedents that are still alive today. Because he only had a daughter passing on the DNA line, DNA from decedents of a paternal uncle of Thomas Jefferson was used to compare their DNA to Sally Hemings's male decedents. a. Based on this description what type of analysis was performed? b. Does this type of analysis guarantee that Thomas Jefferson fathered these children? c. Why couldn't the decedents of Thomas Jefferson's daughter be used for this type of analysis? d. What type of analysis could be performed to trace maternal ancestry?

a) Y-STR analysis

b) No, but it can rule out if he did not

c) Because his daughter cannot pass a Y chromosome on

d) mitochondrial DNA analysis

Explanation:

a) Because they are tracing male lineage, they are likely carrying out Y STR analysis, which looks at short tandem repeats (STRs) on the Y chromosome. Because the Y chromosome doesn't participate in crossing over, it can be reliably traced back generations and trace the paternal line, because it undergoes very little changes over time.

b) Y-STR analysis is not the best for narrowing complete specificity to one person. The Y chromosome is highly unchanged throughout generations, so it is difficult to determine differences between closely related males. However, it can rule out paternity if the Y-STRs between tested males do not match

c) Only his daughter went on to produce direct descendants still alive today. Because she is female, she could not have harbored the Jefferson Y chromosome, any of her male children will have the Y chromosome of their father. Therefore, they have to look at a male elsewhere in the Jefferson family to match the Y chromosomes, hence the paternal uncle.

d) Mitochondrial DNA is often used to trace maternal ancestry. Mitochondria are organelles in the cell that possess a small amount of DNA. This DNA is passed on through the maternal line (because when the sperm and egg fuse during fertilisation, the egg has thousands more mitochondria in the cell, and therefore contributes thousands of times more mtDNA than the sperm).