It’s important to remember there are lots of different mutations that can occur in our DNA. First, we have small scale mutations where we have point mutations that are the change just in one base. Yes, in one base could be cytosine adenine, for example, in the DNA sequence. In the small scale mutations, we could have a substitution, it occurs when one or more bases in the sequence is replaced by the same number of bases. I know it’s a little tricky to understand but for example, a substitution is when for example a cytosine substituted for anatomy that’s another mutation that we have. We could have an inversion, that is, that occurs when the segment, just a segment, of a chromosome is reversed and we have insertion when a base is added to the sequence. All the sequence of the DNA that will form a protein and finally we could have angulation that when the base is deleted from the second so, there are very partial and small scale locations but on the other hand, we could have large scale mutations. We could have a copy number variation which is called CNV, it’s the type of mutations where large chunks of DNA are inserted, repeated or lost. These regions of DNA can be between 1000 and 5 million bases long, very long. We could have duplication of genes when there is an increase in the number of copies of the gene. We could have deletions of larger radians of the chromosome, less of one copy of a gene in an organism that previously had the copies, loss of one copies, movement of sections of DNA from one location to another and finally the most common that we have heard of is an addition of an extra copy of a chromosome, for example, an extra copy or partial copy of chromosome 21 results in Down’s syndrome.
Most mutations, hundreds of genes affecting fertility are found on the non-sex chromosomes. There are mutations that mostly affect male fertility on the X chromosome. For example, on the gene called X11 on the X chromosome and on the Y chromosome, there are DAZ genes So these are deleted in azoospermia genes. If IVF is successful using male sperm from Y chromosome defective patients, then any babies born will, unfortunately, suffer from the same infertile affliction as the father. So couples affected by such mutations could possibly consider Preimplantation Genetic Diagnosis, so only female embryos are implanted. This will avoid having male babies that will be affected by the same infertility problems as the father. In addition, there are rare dominantly inherited mutations that can cause infertility. This means that the male only needs to inherit one bad chromosome and not two to get the disease. For example, there is a rare, inverted DNA sequence on chromosome one. Karyotyping picks that up, and that causes Spermatic Genetic Failure in males who inherit only one bad copy. Fortunately, these mutations are rare. Most things are recessive and not dominant, or X or Y linked.
