How do mutations occur? Are they harmful?
Mutations are changes in the copies of DNA passed from a parent to offspring. They creep into the DNA record in a random way according to their “molecular clock.” In other words, they are not caused by anything. Sometimes the DNA just changes, and this affects a certain position on the long strands of it that are in every cell of your body. In almost all cases, these changes do not do anything. Only in the case of genetic disease do the mutations have any effect on us. Even though they do not do anything, though, they continue to be passed down in exact copies from parent to offspring. So they are useful in identifying individuals who come from the same ancestor. All these descendants are in the same lineage. Once a mutation occurs it identifies that line forever. Descendants are said to be “downstream” from that change. What are alleles? Alleles are different variations of DNA at different positions on the long strands. The positions on the Y chromosome are called DYSs or loci (plural
