Final answer:
During gametogenesis and early embryonic development, methylation patterns are generally reset, but an exception is genomic imprinting, leading to diseases like Prader-Willi Syndrome and Angelman Syndrome, which result from imprinting errors on chromosome 15.
Step-by-step explanation:
During gametogenesis and early embryonic development, almost all methylation patterns are wiped out (deprogramming) and new patterns are reprogrammed in the lifetime of the organism. An exception to this reprogramming process is genomic imprinting, where genes maintain the methylation pattern they acquired during gamete formation of one parent and are expressed or silenced depending on whether they come from the mother or the father. This can lead to diseases known as imprinting disorders. Two related syndromes caused by incorrect imprinting are Prader-Willi Syndrome (PWS) and Angelman Syndrome (AS). Both syndromes are the result of imprinting errors on chromosome 15 but manifest differently depending on which parent's gene is affected.
PWS is characterized by intellectual disability, hypotonia, and life-threatening obesity, among other symptoms. It occurs when the paternal genes that are normally active in the region are missing or not expressed. AS, on the other hand, includes symptoms like severe intellectual and developmental disabilities, sleep disturbances, and je_rky movements. It arises when the same region on the maternal copy is affected. Both syndromes highlight the importance of proper epigenetic regulation and the consequences of its disturbances. They also underscore the critical role of parental origin in the expression of certain genes.
Understanding that changes in chromatin organization interact with DNA methylation and that errors in these processes can lead to serious genetic disorders is essential for the development of targeted therapies and the study of epigenetics as a whole.