EPIGENETICS
Honors
Biology
TWINS: IDENTICAL OR FRATERNAL?
WHAT IS EPIGENETICS?
 Epi = “on top of”
 Genetics = genetic make up
of an organism
 Epigenetics… what factors,
on top of genes, impact our
genetic make up
SAME GENES, DIFFERENT PHENOT YPES
 A Tale of Two Mice – part I
 Complete Step 1 on Student Worksheet
 What does it mean to say that two individuals are genetically
identical?
 How can two genetically identical mice look so dif ferent?
 Step 2 on Student Worksheet
Condensed
Chromatin
Hydrogen Bonds
(between
bases)
Nucleotide
(consists of a base,
a 5-carbon sugar,
and a phosphate group)
Phosphodiester Bond
(between adjacent nucleotides)
Decondensed
Chromatin
WHAT IS EPIGENETICS?
Refers to changes in gene expression caused
by mechanisms other than changes in the
underlying DNA sequence
Enables a cell/organism to respond to its
dynamic external environment during
development and throughout life!
Epigenetic changes to the genome can be
inherited if these changes occur in cells giving
rise to gametes
TWO EPIGENETIC MECHANISMS
1. Histone Modifications
2. DNA Methylation
Video
1. HISTONE MODIFICATION
If the way that DNA is wrapped around the
histones changes, gene expression can change
(transcription)
2. DNA METHYLATION
The addition of methyl groups to DNA can also
change gene expression (transcription)
 A Tale of Two Mice – part II
 Complete Step 3 on Student Worksheet
 A Tale of Two Mice – parts III-V
 Finish Steps 4-5 on Student Worksheet