Trigger 9: Epigenetics in action Flashcards
during gametogenesis
epigenetic profile is rest to de novo
when genes evade reprogramming
imprinted from previous generations
uniparental disomy
people who inherit both homologous chromosomes from the same parents
what occurs due to uniparentald disomy
loss of expression of some genes that maternal alleles and increased levels of paternally expressed genes
UPD
uniparental disomy
UPD was hypothesised to
cause diseases due to changes in epigenotype and disruption of genomic imprinting
genomic imprinting
where alleles inherited from one parent are expressed differently to the other parents
- e.g. allele from father is inactive due to imprinting
during imprinting the alleles
behave normally in meiosis- only their expression in the offspring is altered
during imprinting what is meaningless
dominants- basically hemizygous
hemizyoug
. A chromosome in a diploid organism is hemizygous when only one copy is present
most common imprinting method
DNA methylation
where does de novo emthylase act only at
CpG islands
after DNA replication
DNA methylation is replicated DNMT1
freshly replicated DNA is methylated only
on one strand (hemi-methylated)
maintenance methylase
acts only at hemimethylated CG sites
will a change in phenotype occur if the maternal copy of gene is imprinted, but the paternal copy is normal
no
will a change in phenotype occur if the maternal copy of gene is imprinted and the paternal copy is mutated
yes
function of genomic imprinting
parental conflict theory
name two genes involved in the parental conflict theory
IGF2
IFF2R
what is the parental conflict theory
imprinting has evolved in mammals because of the conflicting interests of maternal and paternal genes in relation to the transfer of nutrients from the mother to her offspring.
interest of mother
to grow well, but leave some resources for me and my future babies
interest of mother
grow big and strong
- use all the maternal resources
- future babies may not have my alleles
IGF2 and IGF2R in men
IGF2 on
IGF2R off
IGF2
insulin-like growth factor
- stimulates foetus to grow
IGF2 and IGF2R in female
IGF2 off
IGF2R on
IGF2R
insulin-growth factor receptor
- reduces the effect of IGF2
in mammals the GF IGF@ interacts with
IGF2R
in mice the gens for IGF2 and IGF2R are
both imprinted
deleting mother IGF2 receptor genes produces
overly large offspring
deleting the fathers IgF2 gene
produces award offspring
deleting the mothers IGF2 and fathers IGF2R
produces normally sized offspring
imprints on IGF2 and IGF2R usually
cancel each other out
changing the imprint on one copy of the gene
has a dramatic effect ton size of offspring
example of imprinted genes
liger and tiglons
father is lion and mother is tiger
very large
father its tiger and mother is lion
normal
different imprinted gene between the mother and father cuases
difference in size and appearance between ligers and tigons
females have
2 alleles X chromosomes genes
males have
1 X chromosome
in mammals the early embryo, the paternal X chromosomes (Xp)
is selectively inactivated in all cells
how is Xp inactivated
by imprinting
when is Xp reactivated
during blastocyst stage
Xp or Xm is randomly
inactivated
the X that is inactivated
stays silent for subsequentt cell generations
