genomic imprinting and dynamic mutation

Question 1

epigenetic trait

Answer 1

heritable (at the level of mitosis) phenotype resulting from changes in a chromosome without any changes to DNA sequence
e.g. DNA methylation, microRNAs

Question 2

DNA methylation

Answer 2

• mainly in promoter region (front end of genes) with G and C
• causes transcriptional silencing
• transmitted through cell division (but not from parents to children as methylation wiped out during embryogenesis)

Question 3

X chromosome inactivation

Answer 3

• methylation contributes
• process of lyonization
  there are multiple mechanisms of inactivation of X chromosomes, methylation plays an important role but other mechanisms contribute

Question 4

genomic imprinting

Answer 4

restriction of expression in either maternal or paternal allele
parent of origin dependent expression of genes
mediated by methylation
e.g. If the allele inherited from the father is imprinted, it is thereby silenced, and only the allele from the mother is expressed

Question 5

application and removal of imprint

Answer 5

female = established during oocyte maturation
male = established prior to meiosis in primary spermatocyte

removal = demethylation at early embryo

Question 6

how can imprinting cause diseases

Answer 6

e.g. if you have deletion of paternal copy of a gene and maternal copy is imprinted (cant be expressed) then the gene is missing and therefore no function

Question 7

name some examples of diseases where genomic imprinting is involved

Answer 7

Prada-willi Syndrome
e.g. paternal allele is deleted and maternal allele is imprinted so can’t take over because it’s silenced
Angelman syndrome
e.g. maternal allele is deleted and paternal allele is imprinted so can’t take over because it’s silenced

Question 8

methylation changes associated with cancer

Answer 8

• inherited predisposition

- somatic methylation changes

Question 9

dynamic mutation

Answer 9

progressive expansion of repeat sequences, mainly triplet repeats e.g. Huntington’s disease

Question 10

anticipation (in dynamic mutations)

Answer 10

the phenomenon that symptoms in later generations occur at an earlier age and are more severe

Question 11

the process involved in genetic counseling

Answer 11

1. evaluate family medical history and risk assessment
2. educate about condition; history, pattern, management, prevention, support
3. counseling to promote informed choices around risks, family, cultural and ethical values
4. support adjustment of lifestyle and risk of reoccurrence in other members