Hales RS 2- Epigenetics Flashcards
What is aneuploidy?
An abnormal amount of chromosomes
What is a Barr Body? What genes are responsible for their formation?
A Barr body is an inactive X chromosome found in cells with more than one X chromosome.
The Xist and Tsix genes play an essential role in this process.
What is a pseudoautosomal region? Is this region susceptible to X-inactivation?
Pseudoautosomal regions are homologous sequences of nucleotides on the X and Y chromosome. Their function is to allow X and Y chromosomes to pair and properly segregate during meiosis in males. These regions escape X-inactivation
How can genes outside of the pseudoautosomal region escape x-inactivation?
X-chromosome genes with homologous genes on the Y chromosome will lead to two active genes, but no crossover.
What is a manifesting heterozygote?
When the dominant allele for a gene that would not be expressed is on the X chromosome that was inactivated, someone with a deleterious gene will express the trait.
Essentially, the wrong X would get inactivated.
What disease would monosomy of the X chromosome lead to? What genetic composition would be due to paternal meiotic error 50% of the time?
Turner’s syndrome
45x is due to paternal meiotic error 50% of the time
What is genomic imprinting?
An epigenetic phenomenon that causes genes to be expressed in a parent of origin specific manner.
One gene copy is silenced by methylation, and only the other copy is expressed. Parent of origin effects
What is the difference between the inheritance of Prader-Wili and Angelman syndrome? What other gene mutation can cause a similar phenotype to one of these?
Both diseases are due to a deletion on the q arm of chromosome 15. If this happens paternally, Prader-Wili will occur. If this happens maternally, Angelman Syndrome will occur.
A deletion in the UBE3A gene can present with a similar phenotype
What causes Beckwith-Weidmann syndrome?
A biallelic expression of IGF2 or silencing of CDKN1C
How can a man with an active, paternally imprinted gene have descendants that are affected?
He will pass the faulty gene to 1/2 of his offspring. It will be reactivated in the descendants of his female children only.
Only females with the faulty gene can have affected offspring
How can a woman with an inactive, maternally imprinted gene have descendants that are affected?
She will pass the gene to her offspring, but it will be inactive
Her sons will pass it on to 50% of their offspring.
Only males with a faulty gene can have affected children.
