Epigenetics Flashcards
What are epigenetics?
Any process that alters gene activity/expression without changing DNA sequence
What is the difference between genetics and epigenetics?
Genetic inheritance involves passing down DNA sequences (genes) from parents to offspring, determining traits through fixed genetic code.
Epigenetic inheritance involves changes in gene expression without altering the DNA sequence, influenced by environmental factors and reversible modifications like DNA methylation or histone modifications.
What are the two processes of epigenetics?
Methylation and DNA packaging
What is methylation?
The addition of CH4 (methane) to DNA
What kind of methylation can silence genes?
Hyper-methylation
What is DNA packaging?
DNA packaging is the process of condensing DNA to fit inside the nucleus. It involves:
Histones – Proteins that DNA wraps around, forming nucleosomes.
Chromatin – DNA + histones, organized as euchromatin (loose, active) or heterochromatin (tight, inactive).
Chromosomes – Fully condensed DNA structures during cell division.
What is heterochromatin?
Tightly-packed DNA. Gene can be hidden/silenced & inaccessible to transcription machinery
What is euchromatin?
Loosely-packed DNA, allows gene expression
What do the epigenetic modifications (methylation and DNA packaging) have in common?
They are both reversible and heritable
What do heterochromatin and euchromatin have in common?
Both are present in a non-dividing nucleus and DNA can switch between both
What is X-inactivation? How does it count as an epigenetic modification?
It silences one X chromosome in each somatic cell in all females. In early development, X in each cell is randomly inactivated. Chromosomes become tightly condensed (Barr body: inactive X.) The same X will be inactivated in each daughter cell.
What are Barr bodies?
Inactivated X chromosomes in female cells, ensuring dosage compensation between males (XY) and females (XX). Importance: gene balance, epigenetic regulation, sex chromosome disorder identification
When do Barr bodies form?
Early embryonic development
What is anhidrotic dysplasia?
when the gene needed for the development of sweat glands is on X chromosome. Males: no sweat glands, Females: both
What is Turner syndrome?
when females have one X chromosome (XO) because some genes are needed in a double dose (45,X) instead of (46,XX). result of nondisjunction in formation of sperm or egg
How can an individual with a monosomy survive through adulthood when autosomal monosomies are lethal?
An individual with Turner syndrome (45,X) survives because the X chromosome is different from autosomes. (sex chromosome)
The X chromosome carries fewer vital genes compared to autosomes. Autosomal monosomies are lethal because they remove essential genes needed for survival.
What happened when agouti mice were treated with DNA methylating agents?
Gene Silencing – The Agouti gene is turned off, preventing excessive yellow fur and obesity.
Healthier Offspring – Pups are more likely to have brown fur, normal weight, and lower disease risk.
Epigenetic Inheritance – These methylation patterns can persist through generations, influencing offspring traits without changing DNA sequences.
What is an operon?
A group of genes that is transcribed together into a single mRNA molecule. Regulation of operons involves negative control of genes (turning them off).
What is a repressible operon?
an operon where transcription is usually on but can be inhibited (repressed) when a specific molecule binds to a regulatory protein
What is an inducible operon?
an operon that is usually off but can be stimulated to be on
what are inducible enzymes?
enzymes where synthesis is induced by a chemical signal
what are repressible enzymes?
enzymes which function in anabolic pathways
what is an activator in gene expression?
a protein that binds to DNA and stimulates the transcription of a gene
what is an epigenome?
The body’s complex chemical network that controls gene expression. Everyone has a unique, changeable epigenome.
What is a methyl molecule?
A molecule that can turn off (silence) genes (CH3)
How can an epigenome be changed and passed on?
Diet, behavior, surroundings, environmental pollution, smoking. Epigenetic signals from environment can be passed one generation to the next.
When is the critical period for passing on epigenetics?
Gamete formation
Which genes involved in cell cycle control and cancer should be targets for methylating drugs in cancer?
Abnormal DNA methylation can silence tumor suppressor genes or activate oncogenes, disrupting normal cell cycle control. Targeting these genes with methylating drugs could potentially reverse or modify the epigenetic alterations.
What have twin studies revealed about epigenetics?
Identical twins (monozygotic) have the same DNA sequence, however, epigenetic differences (such as DNA methylation and histone modifications) can cause differences in gene expression, leading to some variations in traits and susceptibility to diseases, even though their genetic code is identical. So, while their genes are the same, their gene expression can differ due to environmental factors.
What were the critical periods for grandparents in the Overkalix studies, investigating how grandparents’ diets and environmental factors could influence the health and traits of their descendants?
Critical times identified in these studies include:
Grandfather’s diet during childhood: If a grandfather experienced poor nutrition during childhood, it was linked to an increased risk of diabetes in his grandchildren.
Grandmother’s diet before conception: When a grandmother experienced food scarcity before conception, it affected the grandchildren’s cardiovascular health and lifespan.
These findings suggest that early-life nutrition of grandparents, particularly during critical periods such as childhood and pre-conception, can epigenetically influence the health of future generations.
