BIOL 311 Lecture Notes - Lecture 28: Small Nuclear Ribonucleoprotein Polypeptide N, Epigenome, Methylation

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Published on 13 Dec 2017
Th e Epige n o m e
- The epige nome consis ts of the se t of che mica l modifications ma de to:
- Prote ins tha t a s s ociate with DNA
- Che mica l modifications do not cha nge the sequence of the DNA or the se que nce of a mino
acids in the prote ins
- The che mica l cha nges e ithe r allow or pre ve nt ge ne expres s ion and are inhe rita ble
- Che mica l modifications to DNA
- Methylation of C a nd G nitroge nous base s in DNA
- Pre vents transcription sile ncing trans cription
- Pa tte rn is inhe rite d
- Pa tte rn of me thylation can differ de pe nding on whethe r the organism is ma le or fe ma le (i.e.
is se x-spe cific)
- Exa mple : Pra der-Willi Syndrome
- Ca use d by a dele tion of the S NRPN ge ne on chromos ome 15. Let’s ca ll the WT a lle le
S+, and the dise a se a lle le S . A he terozygous pe rs on (S+/S) ca n e ither be born with the
dis e as e , or live the ir life with no s ign of it. Whethe r or not a pe rson ge ts the dis ea s e
depends on which pa re nt pas s es on the dis e a s e alle le . Why?
- Look a t the cros s : Mom (S+/S) x Dad (S+/S+)
- Although the male doe s not ha ve the
dis e as e , the ir kids ca n ha ve the dis e a s e
if the y are hete rozygous. Why?
- Looking at the S locus in the somatic
ce lls in the ma le he terozygote :
- Methylation at this locus is se x-spe cific
and sile nce s ge ne e xpre s s ion
- The addition of the methyl tags a t this
locus only occurs in female s
- So wha t happens in the ma le during
me ios is ? The me thyl tags he inhe rite d
from his mom are removed in his ge nre
ce lls . Two poss ible ga me tes are ma de
(s e cond picture on s ide):
- Fe male homozygous for wild-type (third
picture on side)
- Only one type of ga mete is ma de by the
fe ma le (fourth picture on side)
- During ga mete forma tion in me ios is , she
will a d d me thyl tags to the copy of the
gene s he inhe rite d from he r da d
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