L13

Question 1

Epigenetic modifications are:

Answer 1

• chemical tags on DNA or proteins associated with DNA modulating gene expression patterns
• do NOT change the sequence of DNA
• induce or inhibit gene transcription

Question 2

DNA methylation: 5mC

Answer 2

• occurs at CG bonds
• detected by sodium bisulfate reaction: converted unmethylated C into T
• is heritable, can be sex-specific

Question 3

Genomic imprinting

Answer 3

• A gene inherited from one of the parents is not expressed, even though both gene copies are functional
• Imprinted genes are methylated and therefore inactive
  Maternal imprinting: gene active only in paternal allele
  Parental imprinting: gene only active in maternal allele

Question 4

Dosage compensation

Answer 4

• To avoid imbalance in X-linked gene transcription, one of the X chromosomes is inactivated in the early stages of development
• Inactivated X-chromosome is called a Barr body
• choice of paternal or maternal X chromosome inactivation in each cell is random
• Inactivated X chromosome remains inactive for lifetime of cell and its daughter cells
• Inactivation only happens in female cells carrying 2 X chromosomes