Epigenetics refers to external modifications to DNA that turn genes on or off without changing the DNA sequence. Common epigenetic modifications include methylation, where methyl groups are added to DNA, turning genes off, and histone modification, where histone proteins package DNA in a way that makes it accessible or inaccessible. Epigenetics explains why different cell types have different gene expression from the same DNA and can be inherited through generations. While epigenetic reprogramming normally erases marks between generations, some examples show epigenetic inheritance in plants, fungi, and animals. Epigenetic changes also play a role in certain cancers by silencing tumor suppressor genes or DNA repair genes.

1. EPIGENETIC
KASHAF - SP18-BSI-025

2. CONTENTS
• What is epigenetics.
• Epigenetic modifications
• Epigenetic changes
• Methylation
• Histone modification
• Epigenetics is the reason
why brain cells differ
from skin cells
• Epigenetic inheritance
• Reprogramming
• Examples of Epigenetic
Inheritance
• Epigenetics and cancer

3. What is epigenetics
• Epigenetics literally means "above" in Greek or
"on top of" genetics.
• It refers to external modifications to DNA that
turn genes "on" or "off."
• These modifications do not change the DNA
sequence

4. Epigenetic modifications
• Epigenetic modifications remain as cells divide
and in some cases can be inherited through the
generations.
• Environmental influences, such as a person’s
diet and exposure to pollutants, can also impact
the epigenome.

5. Epigenetic changes can help:
• Determine whether genes are turned on or off.
• Influence the production of proteins in certain
cell.
• ensuring that only necessary proteins are
produced.
• Alter the physical structure of DNA.

6. For example
• proteins that promote bone growth are not
produced in muscle cells.
• Patterns of epigenetic modification vary among
individuals, different tissues within an individual,
and even different cells.

7. Methylation
• A common type of epigenetic modification is
called methylation.
• Methylation involves attaching small molecules
called methyl groups or a "chemical cap,".
• each consisting of one carbon atom and three
hydrogen atoms, to segments of DNA.

8. • When methyl groups are added to a particular gene, that gene is
turned off or silenced, and no protein is produced from that gene.
• Reason:
• Because errors in the epigenetic process.
• such as:
• Modifying the wrong gene or failing to add a compound to a
gene.
• Can lead to abnormal gene activity or inactivity
• They can cause genetic disorders:-
• Conditions including:
 Cancers
 metabolic disorders
 degenerative disorders
• have all been found to be related to epigenetic errors.

9. Histone modification
• Histones are proteins that DNA wraps around.
(Without histones, DNA would be too long to
fit inside cells.)
• If histones squeeze DNA tightly, the DNA
cannot be "read" by the cell.
• Modifications that relax the histones can make
the DNA accessible to proteins that "read"
genes.

11. Epigenetics is the reason :
• Reason why a skin cell looks different from a
brain cell or a muscle cell.
• All three cells contain the same DNA, but their
genes are expressed differently .
• (turned "on" or "off"), which creates the
different cell types.

12. Epigenetic inheritance
• .We used to think that a new embryo's
epigenome was completely erased and rebuilt
from scratch.
• But this isn't completely true. Some epigenetic
tags remain in place as genetic information
passes from generation to generation, a process
called epigenetic inheritance.

13. • Epigenetic inheritance is an unconventional
finding. It goes against the idea that inheritance
happens only through the DNA code that passes
from parent to offspring. It means that a parent's
experiences, in the form of epigenetic tags, can be
passed down to future generations.
• As unconventional as it may be, there is little
doubt that epigenetic inheritance is real. In fact, it
explains some strange patterns of inheritance
geneticists have been puzzling over for decades.

14. Reprogramming
• Most complex organisms develop from
specialized reproductive cells.
• Two reproductive cells meet, then they grow
and divide to form every type of cell in the adult
organism.
• In order for this process to occur, the
epigenome must be erased through a process
called "reprogramming.“

15. • Reprogramming is important because eggs and sperm
develop from specialized cells with stable gene
expression profiles.
• In other words, their genetic information is marked
with epigenetic tags. Before the new organism can grow
into a healthy embryo, the epigenetic tags must be
erased.
• At certain times during development (the timing varies
among species), specialized cellular machinery scours
the genome and erases its epigenetic tags in order to
return the cells to a genetic "blank slate." Yet, for a
small minority of genes, epigenetic tags make it through
this process and pass unchanged from parent to
offspring.

16.  Reprogramming resets the epigenome of the early
embryo so that it can form every type of cell in the
body.
 In order to pass to the next generation, epigenetic
tags must avoid being erased during reprogramming

18. Examples of Epigenetic Inheritance
• There is no doubt that epigenetic inheritance
occurs in plants and fungi. There is also a good
case for epigenetic inheritance in invertebrates.
• While many researchers remain skeptical about
the possibility of epigenetic inheritance in
mammals, there is some evidence that it could
be happening.

19. Water flea (Daphnia)
• Female water fleas respond to chemical signals from
their predators by growing protective helmets.
• The offspring of helmeted water fleas are also born
with helmets - even in the absence of predator signals.
• This effect continues to the next generation, though the
helmets in the grandchildren are much smaller.

20. Toadflax(Linaria vulgaris)
• Common toadflax and peloric toadflax are identical in every
way, except for the shape of their flowers.
• They are two variants of the same plant with a difference in one
gene. But it’s not a difference in the DNA code.
• It’s an epigenetic difference. And peloric toadflax can pass on
this “epi-mutation” to its offspring.

21. Wild radish
(Raphanus raphanistrum)
• When radish plants are attacked by caterpillars, they produce
distasteful chemicals and grow protective spines.
• The offspring of caterpillar damaged, radishes also produce
these defenses, even when they live in a caterpillar-free
environment.
• The evidence of epigenetic inheritance in this case is indirect,
though it’s highly likely that the information passes from parent
to offspring through the reproductive cells.

22. Epigenetics and cancer
• Scientists now think epigenetics can play a role in
the development of some cancers.
• For instance, an epigenetic change that silences a
tumor suppressor gene — such as a gene that keeps
the growth of the cell in check — could lead to
uncontrolled cellular growth. Another example
might be an epigenetic change that "turns off"
genes that help repair damaged DNA, leading to an
increase in DNA damage, which in turn, increases
cancer risk.

23. Epigenetic fingerprint
• Feinberg and his colleagues scanned the genetic
information of 74 people from Iceland, using DNA
samples taken in 1991 and 2002.
• Specifically, the researchers were looking for areas of the
DNA strand that varied between individuals in terms of
how many genes underwent DNA methylation.
• They found 227 such regions. Because many genes have
the same methylation pattern from person to person, the
researchers said the methylation of these 227 regions
basically represents an epigenetic "fingerprint" unique
to each person.

24. • The results also showed that these fingerprints, for the
most part, remained relatively stable in each person
over the 11-year period. About two-thirds of the 227
regions did not change considerably over that time,
which indicated that the fingerprints are a lasting part
of a person's cell chemistry, not just a fleeting chemical
blip.
• The researchers then looked to see whether these
fingerprints were related to body mass, and found 13
regions in which they were. These 13 regions were on
or near genes previously suspected of playing a role in
obesity and diabetes, the researchers said.