def on imprinting
parental origin specific differential gene expression
via epigenetics
(gamete of origin dependent modification of genotype)
where is imprining found
eutherian mammals
marsupials
flowering plants
mechanism imprining happens through
epigenetic instructions in paretnal germ cells
key molecular mech on imprinting
dna methylation
parthenogenetic embryo
PG embryo
2 copies of maternal genome NO paternal genome
androgenetic embryo
AG embryo
2 copies of paternal genome
summary of results of uniparental embryo experiment
mat genome aids development of foetus
pat genome = extra embryonic tissues
genes on both germ cells in the ovary or the testis are selectively switched off
goals of paternally expressed gene
extract more resources from mohter to benefit offspring fitness
goals of mat expressed gene
conserve resources
divide resources across more offspring
maximise reproducive performance of femal
parental conflict hypothesis
imprinting evolved as a result of conflicting interests between pat and mat genes
example of pat imprinted gene that acts during embryogenesis
peg1
gene product is a hydrolase enzyme
* Promotes:
○ Placental growth
○ Trophoblast expansion
* Supports nutrient supply to the fetus
Effect on embryonic growth
* Acts as a growth-promoting gene
* Loss of PEG1 (paternal allele mutation):
○ ↓ fetal growth
○ ↓ placental size
○ Developmental defects
* Linked to:
○ Maternal behaviour
○ Postnatal growth regulation
* Knockout studies in mice show altered nurturing behaviour
or
Asci2
helix-loop-helix transc fctor
contributes to spongiotrophoblast development
* Maintains trophoblast progenitor cells
* Prevents premature differentiation
Allows continued placental growth and expansion
example of mat imprinted gene
Phida2
pleckstrin homology domain protein
spongiotrophoblast restriction
coadaptation hypothesis
fitness of offspring determined by the interaction of mum and offsprings phenotypes
if silencing a patrigenic allele leads to better interaction between the mum and offspring phenotype then it is silenced
chimaera experiment result
chim mice survived as long as they have less than 40% of pg/ag cells
characteristics of PG-N mice
large brain
small body
inc brain:body weight ratio
increased aggressive behaviour in male PG-N
characteristics of AG-N
small brain
large body size
reduced brain:body weight ratio
where do PG cells conc in the brain
vcognitive function
where do AG cells conc in the brian
emotional and autonomic function
