Summary
Highlights
Genetic disorders are caused by changes in DNA sequence, leading to mutations within genes, altered chromosome numbers, or structural changes in chromosomes. This video focuses on disorders resulting from abnormal chromosome numbers, a condition called aneuploidy. Nondisjunction, the failure of chromosomes or chromatids to separate during meiosis, results in gametes with too many or too few chromosomes. While often causing non-viable offspring, aneuploidy can lead to observable genetic disorders.
Polyploidy describes organisms or cells with more than two sets of chromosomes, such as triploid (three sets) or tetraploid (four sets) organisms. While polyploidy often leads to miscarriage in humans, it is common in plants and results in larger cells. Examples include seedless triploid bananas and watermelons, which are larger and lack seeds.
Down syndrome, or trisomy 21, is caused by an extra copy of chromosome 21. Individuals often exhibit distinct physical traits like small noses, broad hands, upward-slanted eyes, a flat back of the head, and impaired cognitive abilities. The severity of symptoms varies. About 1 in 800 babies are born with Down syndrome, and the risk increases significantly with maternal age, particularly for mothers over 35. Besides nondisjunction, translocation (a piece of one chromosome fusing with another) can also cause Down syndrome.
Turner syndrome is a chromosomal disorder affecting females, resulting from nondisjunction of sex chromosomes, where females receive only one X chromosome. This missing X chromosome impacts development. Females with Turner syndrome are typically short, have underdeveloped ovaries leading to infertility, and may experience other symptoms like skin folds on the neck, kidney problems, swelling of the hands, and heart defects.
Klinefelter syndrome is another condition caused by nondisjunction of sex chromosomes, affecting males who end up with two X chromosomes and one Y chromosome (XXY). This aneuploid condition is a trisomy that interferes with normal male sexual development, leading to female-like features. Affected individuals often have improperly developed testes and decreased testosterone levels. The symptoms vary greatly, with some individuals showing no physical traits and only discovering the disorder when seeking fertility treatment due to infertility.