30 - HIPFNER 3 Flashcards
what is mendel’s laws (reminder) and therefore what is non-mendelian genetics
what is dosage compensation by X-chromosome inactivation
females have 2 X chromosomes, in theory they should be expressing double the amount of the genes present on the X chromosome
but there is “dosage compensation” so that males and females have equal expression levels of the 1000 genes located on the X chromosome
in the early female mammalian embryo (8-32 cells) each cell randomly inactivates one of the two X chromosomes and forms a “Barr body”
the same X chromosome is inactive in all descendants of a given cell: “mitotic” epigenetic inheritance
the fact that the inactivation of either of the two X chromosomes is random can lead to unexpected genetic consequences
example of tortoiseshell cats
this is non-mendelian inheritance of coat color due to X-chromosome inactivation= not every cell is gonna inactivate the same one
example of red green blindness
red green color blindness is due to the mutation of the OPN1-LW on the X chromosme
mut/Y males are colour blind, but mut/+ females are sometimes colorblind but also don’t have to be
if only half of the cells are mutant (in theory) that is enough to not be color blind
but if there is “skewed X inactivation” they may be color blind
in many X linked mutations females have partial symptoms with variable penetrance and expressvitiy
some diseases like Rett syndrome are only seen in females because mut/Y males are not viable
which enzymes methylate DNA and in what context
CpG cytosines are methylated
what is the distribution of CpG regions
what are the ways in which CpG methylation can repress/silence gene expression
how is DNA methylation passed on through mitosis
DNMTs have high affinity for hemimethylated sites, in order to replicate the methylation on the other strand
DNMTs are then guided by methylation patterns on the parental strand
DNA methylation is heritable
why is the inheritance pattern of the Igf2 gene unusual and what is the gene
what is genomic imprinting
how does imprinting work on the Igf2 and H19 genes
what is the effect of those methylations on the expressions of Igf2 and H19
when are imprints established and how?
although few, imprinted genes play important roles in embryonic development
how does imprinting and disease inheritance work, and how does the mutation act?
how does faulty imprinting lead to a disease
not enough methylation on the paternal ICR, thus CTCF can bind to this region and turn off Igf2 expression
since the maternal gene is already imprinted, this will lead to dwarfism as both alleles on both chromosomes are silenced
