Trisomy – Possession of 3 copies of a chromosome instead of the normal 2.
Trisomies occur in non disjunction events: when chromosomes do not properly separate during the production of gametes (egg or sperm). In that scenario, an embryo conceived from gametes with improper number of chromosomes may be missing or have more than the normal number of chromosomes. In these cases – spontaneous abortions usually occur because the embryo is not viable due the lack of or the abundance of the chromosome in question. A very common disorder that results from a trisomy is trisomy 21 – Down Syndrome. In autosomes, a trisomy usually produces a non viable embryo. However, if a trisomy occurs in the sex chromosomes, the embryo is viable will most likely develop. There are a bunch of different variations of the trisomies.
In a normal biological female and male, the sex chromosome are XX and XY respectively. However, a trisomy can cause XXX, XXY, or XYY to occur. In these cases, the people that possess these combinations can live a relatively normal life.
People with XYY have a disorder called “Jacob’s Syndrome”. Jacob’s Syndome has also been dubbed “XYY Supermale”. The reason why is that the extra Y chromosome causes a dosage problem. Even though females may have two copies of the XX chromosome – one is inactivated to compensate for the dosage issue that might occur. However, the extra Y in this case, can not be inactivated. The dosage issue caused by the extra Y can have dramatic effects.
The following signs may be an indication that a young boy or teenager has XYY Syndrome:
- an autism diagnosis
- an inability to grow facial or body hair
- attention difficulties
- delayed motor skill development, such as writing
- delayed or difficult speech
- delayed or absent puberty
- emotional or behavioral issues
- gynecomastia, or enlarged breast tissue
- hand trembling or involuntary muscle movements
- hypogonadism, or low testosterone levels
- hypotonia, or weak muscle tone
- learning disabilities
- low energy levels
- small penis
- small, undersized testicles
- taller than average height
- weak bone
taken from: http://www.healthline.com/health/xyy-syndrome#Symptoms4
The reason why we spent quite a bit of time on this particular syndrome was that, in the past there was a huge issue about association of genetics and behavior. There was study done in the early 20th century with looking at the karyotypes of prisoners. They found that in the prison population compared to the general population, the prevalence of Jacob’s Syndrome was slightly higher. This was later debunked with further research. However, it brought about the debate on whether or not genetics predetermines behavior. Professor Ralph Bertrand presented the question of whether or not it was right to test for Jacob’s Syndrome at birth just like one would be tested for Cystic Fibrosis or Phenylketonuria. He asked about the rightness or wrongness of such testing because the results may then change the way the parents and society treats children who have been labeled at birth to be “future criminals”. Some students said it was wrong to do such testing because genetics is not destiny. Some students said the test should take place in order to give children with this disorder the proper care and education. Such subject exist in the realms of ethical purgatory. In the end, behavior is so complicated – that the explanation of having an extra Y predetermines criminal activity is simply inadequate.