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EMS > Lecture 38: Genomic imprinting and epigenetics > Flashcards

Lecture 38: Genomic imprinting and epigenetics Flashcards

1
Q

What is the term used for reproduction using just male genetic material?

A

androgenesis

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2
Q

Why can’t we reproduce asexually?

A

Two parents are required for mammalian development

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3
Q

What is androgenesis?

A

Androgenesis is a method for producing fish in which all the nuclear genetic information originates from the male parent (i.e., from the sperm) while the mitochondrial DNA is still maternally derived.

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4
Q

What is the term used for reproduction using just female genetic material?

A

parthenogenesis

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5
Q

What is pathenogenesis?

A

reproduction from an ovum without fertilization, especially as a normal process in some invertebrates and lower plants

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6
Q

What does androgenetic conception form in humans?

A

hydatidiform mole

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7
Q

What does parthenogenetic conception form in humans?

A

ovarian teratoma

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8
Q

What is a hydatidiform mole?

A

a cluster of fluid-filled sacs formed in the uterus by the degeneration of chorionic tissue around an aborting embryo / Benign tumour of trophoblastic tissue which develops at the placenta which may become malignant

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9
Q

What 3 tissues are not seen in ovarian teratomas?

A

1) skeletal muscle

2) membranes

3) placenta

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10
Q

What do androgenetic embryos usually result in? (3)

A
  1. Complete hydatidiform moles
  2. Proliferation of abnormal trophoblast tissue
  3. Can develop into malignant trophoblastic tumour
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11
Q

What is the usually genetic identification of androgenetic cells?

A

Mostly homozygous 46,XX

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12
Q

What are ovarian teratomas?

A

a bizarre tumor, usually benign, in the ovary that typically contains a diversity of tissues including hair, teeth, bone, thyroid, etc

A dermoid cyst develops from a totipotential germ cell (a primary oocyte) that is retained within the egg sac (ovary).

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13
Q

How are ovarian teratomas formed: Pathenogenetic or androgenetic?

A

Parthenogenetic conceptions

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14
Q

What is genomic imprinting?

A

an epigenetic phenomenon that causes genes to be expressed or not depending on whether they are maternal or paternal

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15
Q

How do ovarian teratomas form?

A

Derived from oocytes which have completed first or both meiotic divisions

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16
Q

Name 5 characteristics of ovarian teratomas?

A
  1. Diploid
  2. Wide spectrum of tissues
  3. Predominantly epithelial
  4. No skeletal muscle
  5. No membranes/placenta
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17
Q

Why do pathenogenetic embryos die?

A

embryos die due to failure of development of extraembryonic structures
(Trophoblast
Yolk sac)

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18
Q

Why do androgenetic embryos die at 6 somite stage?

A

Well developed extra-embryonic membranes
Poor embryo development

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19
Q

Why do uni parental conceptions fail?

A

Different roles of maternal vs. paternal genes in determining developmental fate

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20
Q

What are karyotypes and gene dosage like in uni parental conceptions?

A

Normal

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21
Q

What is genomic imprinting?

A

A mechanism that ensures the functional non-equivalence of the maternal and paternal genomes

Mothers and fathers somehow “imprint” their genes with a memory of their paternal or maternal origin

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22
Q

Is genomic imprinting encoded in the DNA nucleotide sequence?

A

No

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23
Q

When does genomic imprinting occur?

A

gametogenesis

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24
Q

True or false: genomic imprinting affects a very small subset of 100-200 genes

A

true

25
Q

What in the genome does genomic imprinting affect?

A

Affects the expression of a small subset of 100-200 genes
Evolutionarily conserved

Depends on modifications to the genome laid down during gametogenesis

26
Q

What is Angelman Syndrome?

A

a congenital condition characterized especially by intellectual disability and uncoordinated movement, typically resulting from loss of function of a gene present on the copy of chromosome 15 inherited from the mother

27
Q

What are 4 symptoms of Angelman Syndrome?

A
  1. Facial dysmorphism (Prognathism, wide mouth, drooling Smiling/laughing appearance)
  2. Mental Handicap (Microcephaly
    Absent speech)
  3. Seizure disorder
  4. Ataxic, jerky movements
28
Q

What is Prader- Willi syndrome?

A

a rare congenital condition characterized by excessive appetite, often leading to morbid obesity, and a variety of other signs including intellectual disability, short stature, and underdevelopment of the sexual organs, caused especially by the absence of certain genes normally present on the copy of chromosome 15 inherited from the father.

29
Q

Name 5 characteristics of Prader-Willi syndrome?

A
  1. Infantile hypotonia
    (Feeding problems
    Gross motor delay)
  2. Mental handicap
  3. Male hypogenitalism /cryptorchidism
  4. Small hands and feet
  5. Hyperphagia (Obesity)
30
Q

What genetic change causes both Angelman and Prader-Willi syndrome?

A

a deletion at chromosome 15

31
Q

Is the deletion at chromosome 15 on the maternal or paternal chromosome in Angelman syndrome?

A

Maternal

32
Q

Is the deletion at chromosome 15 on the maternal or paternal chromosome in Prader-Willi syndrome?

A

Paternal

33
Q

Name a cytogenetic abnormality in AS/PWS?

A

Deletion of chromosome 15
Found in both Angelman and Prader-Willi syndromes
Always de novo
Recurrence risks very low

34
Q

What is the Molecular mechanisms in Prader-Willi syndrome?

A

Uniparental disomy (25%) vs. del (70%)

Indistinguishable clinically

Lack of a paternal 15q11-13 contribution

35
Q

What are the Molecular mechanisms in Angelman syndrome?

A

Deletion (75%)
UPD (1%)
Point Mutation (2-5%)

36
Q

What is the key mechanism of genetic imprinting?

A

DNA methylation

37
Q

What enzyme is used to methylate DNA?

A

DNA methyltransferase enzymes

38
Q

True or false: DNA methylation is irreversible

A

False

39
Q

Where does DNA methylation occur?

A

CpG islands (and CG nucleotides)

40
Q

Does a methylated CpG island express or silence a gene?

A

Silence

41
Q

Give three ways in which chromatin can be molecularly modified:

A

1) phosphorylation

2) methylation

3) acetylation

42
Q

What enzyme aids methylation of histones?

A

histone methyltransferase

43
Q

What enzyme aids phosphorylation of histones?

A

protein kinases

44
Q

What enzyme aids the removal of acetyl groups from histones?

A

histone deacetylase

45
Q

Why do parental genes favour large babies?

A

it correlates with high foetal fitness

46
Q

Why do maternal genes favour small babies?

A

it correlates with better maternal survival rate and reproductive fitness

47
Q

What is Beckwith-Wiedemann syndrome?

A

large foetus syndrome (foetal overgrowth, organomegaly)

48
Q

What is Russel-Silver syndrome?

A

small foetus syndrome (growth retardation, triangular face)

49
Q

What gene is affected in both Beckwith-Wiedemann syndrome and Russel-Silver syndrome?

A

11p15.5

50
Q

What causes Russel-Silver Syndrome?

A

hypomethylation causing both the maternal and paternal IGF2 genes to be silenced

51
Q

What is the role of the IGF2 gene?

A

foetal growth promotion

52
Q

What causes Beckwith-Wiedemann syndrome?

A

hypermethylation causing both maternal and paternal IGF2 to be expressed

53
Q

True or false: imprinting is preserved in somatic development

A

True

54
Q

What is imprint switching?

A

the swapping of imprinting patterns between paternal alleles to erase grandparental imprints and establish a new parental input

55
Q

True or false: X inactivation is reversed in germ cells

A

True

56
Q

True or false: it is random which X chromosome is inactivated

A

True

57
Q

When does X inactivation occur?

A

early embryogenesis (when blastocyst has formed)

58
Q

What is the name given to the split in cells with paternal vs maternal X inactivation?

A

mosaicism

59
Q

What is the effect of mosaicism on female carriers of X-linked mutations?

A

carriers may present with a partial phenotype for the disease (skewing results in varied clinical expressions)

EMS (54 decks)

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