Genomic imprinting and epigenetics

Question 1

define androgenesis

Answer 1

development dependent on father

Question 2

define parthenogenesis

Answer 2

development dependent on mother.

Question 3

when are the 2 polar bodies pouched out of the egg

Answer 3

1st- pushed out meiotic division 1.

2nd pushed out- after meiotic division 2 which gives rise to the diploid composition.

Question 4

are hydrotidiform mole androgenic or pathogenic`

Answer 4

androgenic

Question 5

what is the composition of a Hydatidiform mole

Answer 5

homozygous 46,XX
Proliferation of abnormal trophoblast tissue.
Can develop into malignant trophoblastic tumour
No embryo

Question 6

which structure hyperprolifearates in hydatidiform mole

Answer 6

trophoblast.

Question 7

what teratoma is caused by parthenogenesis

Answer 7

beningn ovarian

Question 8

what are benign ovarian teratomas derived from

Answer 8

oocytes which have completed first or both meiotic divisions

Question 9

why do pathogenic embryos dies

Answer 9

failure of development of extra embryonic structures

trophoblast and yolk sac.

Question 10

what structures are present in patharthogenic tumours and what structures are not.

Answer 10

– Predominantly epithelial
– No skeletal muscle
– No membranes/placenta

Question 11

at what month do androgenetic embryos typically die

Answer 11

– 6 month stage

Question 12

what does uniparental conceptions fail

Answer 12

maternal and paternal genes have different structures.
gene dosage is not normal
karyotyping is not normal.

Question 13

define genomic imprinting.

Answer 13

A mechanism that ensures the functional non-equivalence of the maternal and paternal genomes.
if a patronal gene is imprinted it is silenced and only the maternal gene is expressed.

Question 14

where is genomic imprinting encoded because it is not in the DNA nucleotides

Answer 14

epignetics

Question 15

what factor does genomic imprinting rely on

Answer 15

modifications in gametogenesis

spermatogenesis and oogenesis.

Question 16

what are the common clinical signs of angelman syndrome

Answer 16

facial dysmorphism- proganthisms, wide mouth and drooling.
Mental handicap- microcephaly and absent speech.
Seizure disorder
Ataxic jerky movements
Hand jerks up and down.

Question 17

what are the common clinical signs of Prader- will syndrome

Answer 17

Infantile hypotonia-Feeding problems, Gross motor delay.
Mental handicap
Low muscle tone- floppy
Male hypogenitalism/
cryptorchidism
Small hands and feet
Hyperphagia- Obesity
Stereotypic behaviour

Question 18

In which chromosome do abnormalities in angel man and order willis arise due to

Answer 18

chromosome 15

Question 19

lack of maternal DNA on chromosome 15 causes which condition.

Answer 19

angelman

Question 20

lack of paternal DNA on chromosome 15 causes which condition.

Answer 20

Prader willis

Question 21

At what bases dinucleotide does demythylation occur

Answer 21

CG

Question 22

what enzyme carries out DNA methylation

Answer 22

DNA methyltransferase.

Question 23

which areas are spared of DNA methylation

Answer 23

promoter regions spared: CG “islands”

Question 24

what effect does methylating a CpG island have.

Answer 24

inactivate the promoter region gene and hence the translocation as well.

Question 25

what is the function of DNA methylation

Answer 25

gene regulation.

Question 26

example of a condition caused by imprinting problems

Answer 26

Beck with wiedenmann syndrome

Question 27

what is the pathogenesis behind beck with- wiedmann syndrome

Answer 27

hyper methylation causing increased insulin like growth factor 2 which is a major growth promoter

Question 28

clinical symptoms of beck with- wiedmann syndrome.

Answer 28

foetal overgrowth
organomegaly- exomphalos 
hypoglycaemia
asymmetry
tumour risk

Question 29

what is the pathogenesis behind Russell-Silver syndrome

Answer 29

hypomethylation causing decreased insulin like growth factor 2 which is a major growth promoter

Question 30

what are the clinical symptoms of russell silver syndrome

Answer 30

•	Growth retardation
–	Fetal (IUGR) 
–	Persistent postnatal growth failure
•	Triangular face
–	Brain size more preserved
•	Asymmetry
•	Sporadic occurrence

Question 31

when does imprinting take place

Answer 31

gametogenesis.

Question 32

X chromosome is larger than the Y so do males of females have a larger amount of DNA content.

Answer 32

females.

Question 33

when must genetic imprinting be remembered and when must it be forgotten

Answer 33

remember in somatic cell division

forget in gametogenesis.

Question 34

what process takes place to silence a full X chromosome in females

Answer 34

X inactivation or lyonisation.

Question 35

what is the difference between imprinting and X lionisation

Answer 35

–	Whole X chromosome is silenced
–	Random choice of parental chromosome
–	Different in different cells
–	Somatic cell clones “remember”
–	Occurs early in embryogenesis
–	Blastocyst

Question 36

what test is used for the Hypohidrotic ectodermal dysplasia.

Answer 36

– Starch/iodine test

– Patches of skin with or without sweat glands

Question 37

what is Hypohidrotic ectodermal dysplasia and what inheritance is it.

Answer 37

X-linked mutation

sweat glands have a abnormal distribution.

Question 38

random skewing in X inactivation- what problems can this cause

Answer 38

Increase the number of X linked mutation is females if the normal gene is switched of and the other gene remains on.