Topic 19 Diploid but not really

___% of cytosines methylated in eukaryotes

10%

• primarily on CpG islands near promoters

enzyme that methylates cytosines

DNA methyltransferase

• add methyl groups to DNA de novo and then to all newly synthesized DNA

what does methylation of DNA do

• histones wrap DNA more tightly → RNA pol can’t transcribe

• inhibits binding of activator protein to enhancer

• methyl-CpG-binding proteins recruit other proteins that change chromatin to closed conformation

Epigenetics example : X inactivation

X chromosomes over 1 get shut off

• Barr body → condensed inactivated X chromosome

• Xist gene in Xic (X-inactivation center) encodes RNA that chooses which X chrom gets randomly shut off

• chrom is heavily methylated and shut down in all somatic cells; germ line is reactivated

about ___ of human genes escape inactivation

20-30%

• genes in pseudoautosomal region

• XIST

epigenetics example : imprinting

inherit regions of chromosomes shut off by methylation

• diff regions shut off by mom and dad → if same region shut off on both chrom you’re dead

Angelman syndrome

deleted region inherited from mom

• AS gene silenced in sperm

• offspring does not carry an active copy of the AS gene from sperm or egg

Prader-Willi syndrome

deleted region inherited from dad

• PWS gene silenced in egg

• offspring does not carry active copy of PWS gene from sperm or egg

nutrigenomics

influence of diet on genome

• how nutrients affect gene expression and impact health

• influencing methylation patterns on genes

nutrigenetics

gene variants that affect response to diet

• how individual genetic differences influence how body responds to certain foods

transgenerational inheritance

eg fear of acetophenone in mice