Module 9 Genetics

what is epigenetics

heritable and REVERSIBLE changes to DNA that change when a gene is turned on or off

-unlike mutations, these are not changes to the DNA sequence
-instead, these are changes that affect gene expression

two major parts of gene

-exon (part that encodes for protein)

-enhancer, silencer, intron, promoter (part that determines when and where the gene is expressed)

how does DNA fit into a cell

-DNA gets wrapped up around proteins called histones, which make up nucleosomes
-nucleosomes are protein complexes made up of 8 histone proteins
-this combination of DNA nucleosomes is called the chromatin
-this keeps DNA tightly packed in the cell
-how DNA is packed can affect-how often turned on/off; how likely that peice of DNA is to mutate

what are 2 primary types of changes in epigenetics

1.methylation of DNA
-occurs typically around promoters, enahncers and silencers
-tends to decrease gene expression
2.modification of histone proteins
-tends to affect access to promoters, enhancers and silencers
-tends to increase gene expression
-these changes affect which genes are turned on

what is DNA methylation

-when you add a methyl group to the cytosine nucleotide in DNA
-these methlyations tend to make the DNA more tightly packed
-this makes it harder for RNA polymerase to bind which decreases the expression of the gene
-methyls can be removed (reversible)
-are copied when the cell is copied (mitosis)

what are histone modifications

-many types of histone modifications, including adding acetyl groups to a histone
-these tend to make the chromatin less tightly packed
-makes it easier for RNA polymerase to bind; which increases expression of the gene
-can be removed; and are copied furing mitosis

where do these epigenetic changes come from

the environment: development in utero, chemicals, drugs, aging, diet, disease+stress
-other sources: whether or not an individual had a nurturing mother, an individuals social status, the parasites an individual has in their body

what do we mean when we say epigenetic marks are heritable

-heritability from one cell to the daughter cells it makes via mitosis and/or
-transgenerational epigenetics: heritability of epigenetic marks from one generation to the next
-recent data suggests that first type of heritability is super common
-transgenerational epigenetics is much less common

heritability of epigenetic marks across cells

-when embryos first form, the cells are what we call undifferentiated
-also called stem cells: cells that have the potential to become any type of cell in the body
-these cells then get signals from the developing environment that tell them what kind of cell to become

heritability of epigenetic marks across cells cont.

-signals set epigenetic marks
-these marks then determine which part of the genome get turned on
-this leads to differentiated cells: cells that are a specific type
-the average differentiated cell only expresses 10-20% of the genes in the genome, which genes they express are determined by epigenetics

what happens when differentiated cells divide via mitosis

-the two new cells it makes inherit its epigenetic marks
-and they are of the same type as the original cell
-this is why stem cells are so important: these cells dont have that many epigenetic marks and can become any other cell if it gets the right signals

what is transgenerational epigenetics

-a baby inherits the same epigenetic marks as its mother and /or father
-in a way its like the environment of our parents can affect our genetics, even if we are in a different environment
-also are super rare- it only occurs at a small fraction of genes (<0.1% of genes)

why is transgenerational epigenetics so rare?

-because of reprogramming
-reprogramming is the erasing of epigenetic material
-can occur many time throughout development

what is personal genomics

-the sequencing and analysis of a single person’s genome, typically for medical applications