Gene Dosing & Genomic Imprinting

Question 1

what kind of expression majority of genes?

Answer 1

bi-allelic

Question 2

what mechanisms are involved in X-chromosome inactivation? 3 things

Answer 2

epigenetic mechs

1. histone mods
2. DNA meth
3. non-coding RNAs

Question 3

mono-allelic expression sufficient?

Answer 3

Many are

Some it’s not like autosomal dominant, aneuploidies

Question 4

When is mono-allelic expression essential?

Answer 4

many in imprinted genes

Question 5

The inactive X is called?

Answer 5

Barr body

Question 6

what starts the X-chromosome inactivation process? then what spreads?

Answer 6

Xist and long non-coding RNA, then leads to heterochromatin spread and DNAmethylation

Question 7

is the same X inactivated in all cells?

Answer 7

Nope. Most women are mosaic.

Question 8

How does X-inactivation affect daughter cells?

Answer 8

that first choice of X-chromosome inactivation during an embryo is passed down to daughter cells

Question 9

when do you get X-chromosome inactivation?

Answer 9

early embryogenesis

Question 10

are all genes on the inactivated X-chromosomes affected?

Answer 10

nope. some genes escape as they need to be expressed bi-allelically also Turner Syndrome proof that you need the Barr body

Question 11

4 causes of disruption of imprinting:

Answer 11

1. loss of heterozygosity (microdeletions)
2. uniparental disomy
3. epimutations
4. point mutations

Question 12

Maternally expressed genes tend to do what?

Answer 12

limit fetal growth

Question 13

Paternally expressed genes tend to do what?

Answer 13

promote fetal growth

Question 14

Imprints in gametogenesis?

Answer 14

Erased and re-establish and maintained in embryogenesis

Question 15

what does genomic imprinting mean?

Answer 15

parental origin of a particular gene is ‘marked’ by a reversible epigenetic mechanism

Question 16

are all imprinted genes uniform through tissues?

Answer 16

Nope. IGF-2 imprinted, but also biallelic in brain, liver and chondrocytes

Question 17

What is Beckwith-Wiedemann Syndrome big presentation?

Answer 17

macroglossia
60% epimutation on materal allele
9x great risk if IVF

Question 18

Prader-Willi syndrome deficiency of?

Answer 18

deficiency: Paternally-expressed genes

Question 19

Angelman syndrome deficiency of?

Answer 19

deficiency in maternally expressed genes

Question 20

if you don’t have parent of origin effect, you can get?

Answer 20

Parthenogenesis: ovarian teratomas
Androgenesis: complete hydatiform moles and choriocarcinomas