Genetic Imprinting

Question 1

What is epidemiology?

Answer 1

the study of mitotically and or meiotically heritable changes in gene function that cannot be explained by changes in DNA sequences

Question 2

how does epigenetics relate to imprinting?

Answer 2

gene silencing through methylation patterns on DNA

Question 3

what is genetic imprinting?

Answer 3

autosomal genes are inherited in a silenced state from 1 parent and a activated state from the other parent

Question 4

what is hemizygous?

Answer 4

only one gene is active or correctly expressed

Question 5

when does imprinting take place?

Answer 5

during gametogenesis before fertilization

Question 6

how is DNA methylation involved in gene silencing?

Answer 6

methylation of promoters can cause the gene to be silenced or by recruiting factors that repress transcription

Question 7

how is DNA methylation involved in gene activation?

Answer 7

mechanism poorly understood, but current model states may prevent binding of transcriptional repressor

Question 8

True or False

Imprinting must be reversible

Answer 8

True

must be wiped clean when gametogenesis occurs to pass da genes

Question 9

what are the characteristics of imprinted genes?

Answer 9

1. clustered together
2. contain maternal and paternal imprinted genes
3. encode both proteins and non-coding RNA’s

Question 10

what are the essential characteristics of the epigenetic mark?

Answer 10

1. modification must be established in gametes

2. allele modifications must be stably maintained after fertilization

Question 11

what causes prader-willi and angelman syndrome?

Answer 11

deletion on long arm of chromosome 15

del 15 q11-q13

Question 12

how does prader-willi syndrome come about?

Answer 12

deletion on the paternal chromosome with deactivated maternal chromosome

Question 13

what is the presentation of patients with prader-willi syndrome?

Answer 13

• obesity
• excessive and indiscriminate eating
• short stature
• small hands and feet
• hypogonadism
• mental retardation

Question 14

how does angelman syndrome come about?

Answer 14

deletion of maternal chromosome with deactivated paternal chromosome

Question 15

what is the phenotype of angelman syndrome?

Answer 15

• unusual facial appearance
• short stature
• sever mental retardation
• spasticity
• seizures

Question 16

what is the main way that you can discriminate phenotypically between angelman syndrome and prader-willi syndrome?

Answer 16

obesity is only present in prader-willi syndrome

Question 17

what is uniparental disomy?

Answer 17

when child receives 2 paternal or maternal chromosome rather than 1 of each

Question 18

what is the most common uniparental disomy?

Answer 18

trisomy 15 from maternal non-disjunction leading to 2 maternal and 1 paternal

Question 19

if trisomy 15 is not compatible with life, how does a uniparetnal disomy occur?

Answer 19

non-disjunction early in gestation

Question 20

how does demethylation of imprinted genes occur?

Answer 20

inhibition of maintenance methyltransferase (DNMT1, or through inactivation of chromatin-remodeling proteins

Question 21

where does erasure and resetting of imprinting occur?

Answer 21

at imprinting centers

Question 22

what does an imprinting center contain?

Answer 22

non-coding DNA sequences that bind imprinter RNA transcripts and recruit DNA methyltransferase (DNMT)

Question 23

what is the function of DNA methyltransferases (DNMT)

Answer 23

complexes that methylate CpG islands located near IC on same chromosome

Question 24

how is imprinting maintained after cell division of somatic cells?

Answer 24

maintenance methylation, have to methylate newly synthesized daughter strand