[Music] a genetic disorder is any one of several diseases resulting in whole or in part but change in the DNA sequence away from the normal sequence these disorders are often inherited there are three ways in which genetic disorders can arise due to mutations within genes due to changes in the number of chromosomes and due to changes in the structure of chromosomes today we're going to focus on disorders resulting from having an abnormal number of chromosomes the process of done disjunction which is when chromosome pairs or chromatids failed to separate during meiosis 1 or 2 respectively can result in gametes having too many or too few chromosomes anytime an organism has an abnormal number of copies of a chromosome it is known as aneuploidy whether the organism has too many or too few chromosomes problems can arise most of the time additional or missing chromosomes cause the resulting offspring not to be viable however sometimes aneuploidy results in changes to the organisms phenotype that is it's observable characteristics when aneuploidy occurs in humans it often results in genetic disorders such as Down syndrome which we will discuss right after we look at a special type of aneuploidy known as polyploidy we use this term to describe an organism or cell that has more than two sets of chromosomes it is possible for certain organisms to end up with 3 sets of chromosomes these are non asked triploid organisms or even four sets known as tetraploid organisms although polyploidy results in miscarriage and humans it is common in plants organisms with these types of chromosome numbers tend to have larger cells an example of a polyploid organism is a triploid banana these fruits tend to be larger in size than other bananas and they lack seeds seedless watermelons are also an example of a tricloid fruit as I mentioned earlier down syndrome is an example of a disorder that arises from having an abnormal number of chromosomes Down syndrome is an example of trisomy 21 it is caused by the presence of all a part of a third copy of chromosome 21 people with this genetic disorder tend to have small noses broad hands with small fingers eyes that slant upward and outward and a flat back of the head they also tend to have impaired cognitive abilities which causes delayed development but the severity of these symptoms vary greatly in affected individuals about 1 in 800 babies born have Down syndrome but the incidence of having a child with Down's increases as the age of the mother increases for reasons that are not clear human females over the age of 35 are 500 times more likely to have a child with Down syndrome than those who are younger while nondisjunction is the most common way for trisomy to occur another event called translocation can also produce Down syndrome in offspring during this event a piece of one chromosome breaks off and fuses with another [Music] turner syndrome is another chromosomal disorder that occurs from nondisjunction during meiosis normally people have two sex chromosomes males have an X and a Y chromosome whereas females have two X chromosomes internal syndrome the female receives only one x chromosome the missing X chromosome impact development before and after birth females with Turner syndrome are often short in stature and the ovaries don't develop normally which usually results in them being infertile other symptoms may include extra folds of skin on the neck kidney problems swelling of the hands and heart defects the last example were going to look at other condition arising from an abnormal number of chromosomes is Klinefelter syndrome Klinefelter's is similar to turner syndrome and that it has to do with a non disjunction of sex chromosomes during meiosis however in this case it impacts males who end up with two X chromosomes and one Y chromosome this aneuploid condition like Down's is classified as a trisomy having two x chromosomes interferes with the normal sexual development in the male and the results in other female features furthermore the testes in affected individuals do not develop properly and the levels of testosterone are greatly decreased the salata variation the way Klinefelter's affects males while many affected individuals show physical traits others will show no symptoms at all in fact this man may not even realize they have the disorder unless they visit a fertility specialist when trying to conceive a child as most affected individuals are infertile you