Imprinting

Question 1

Describe androgenetic embryos

Answer 1

Where the female pronucleus is replaced by the male
Poor embryo development
Extra-embryonic tissues develop normally

Question 2

Describe gynogenetic embryos

Answer 2

Where the male pronucleus has been replaced by the female
Embryonic develpment begins normally
Extra-embryonic tissues develop poorly

Question 3

Describe parthogenetic embryos

Answer 3

Generated from nuclei of immature oocytes

Contain 2 female derived haploid nuclei

Question 4

What is genomic imprinting?

Answer 4

Differential marking of parental alleles of specific genes or chromosome regions during gametogenesis leading to differential expression during development

Question 5

What is the evidence for genomic imprinting?

Answer 5

Gynogenetic embryos, androgenetic embryos

Question 6

What is the kinship theory of genomic imprinting?

Answer 6

AKA parental conflict theory
Nutritional need of foetus met by mother via placenta but at a cost to the mother and her other offsrping
Many imprinted genes involved in growth control

Question 7

What is the evidence for the kinship theory of genomic imprinting?

Answer 7

IGF2 protein and receptor in mice
IGF2 promotes foetal growth and is expressed from paternal allele
IGF2R sequesters excess IGF2 and transports to lysosomes for destruction and is expressed from the maternal allele in mice

Question 8

What is the co-adaptation theory of genomic imprinting?

Answer 8

Imprinted genes have evolved to optimize foetal developlment as well as maternal provisioning and nurturing

Question 9

What is the evidence for the co-adaptation theory of genomic imprinting?

Answer 9

Genomic imprinting arose ~180-210 MYA in mammals - about the same time as viviparity and placentation arose.

Question 10

Describe Beckwith-Weidermann Syndrome

Answer 10

Comgenital overgrowth syndrome
Predisposition to childhood cancers
AD
15% cases familial
Imprinting defects in 80% BWS patients eg epimutations at 11p15 gene cluster
Leads to biallelic IGF2 expression

Question 11

Describe Silver Russell Syndrome

Answer 11

Severe intrauterie and postnatal growth retardation

Opposite epigenetic mutations to BWS

Question 12

Describe Angelman Syndrome

Answer 12

Ataxia
Severe intellectual disability
Happy disposition
70% of patients have a deletion on 15q11-13 on maternally inherited chromosome

Question 13

Describe Prader-Willi syndrome

Answer 13

Hyperphagia
Severe obesity
Intellectual disability
70% of patients have a deletion on 15q11-13 on paternally inherited chromosome