Epigenetics Flashcards
Melanin
Melanin: yellow-black pigment produced in special skill cells called melanocytes which themselves produce structures called melanosomes that contain melanin
Formed from an amino acid tyrosine via enzyme tyrosinase
Large amounts are also produced when melanocytes are stimulated by ultra-violet light from the sun. Therefore individual who lack the enzymes for this process will produce little or no melanin
Environmental Factors
Intellectual development: everyone has a inherited potential but many environmental factors can affect this eg diet
Diet: can effect a number of characteristics like height weight
Height: genetic potential for a certain height may not be achieved due to lack of essential proteins and minerals in diet
Gene Expression
Process of copying information from DNA onto messenger RNA and then translating the message into a series of amino acids to form a protein
Process by which genetic instructions are used to synthesise gene products
Genomic imprinting
When you only inherit one working copy from your parents instead of the usual two
One from mum or dad is silenced usually by DNA methylation during egg or sperm formation.
Epigenetic tags are usually all removed in the formation Of gametes but about 1% of these tags are imprinted.
These imprinted tags usually remain for the life of the organism and can then be reset during egg or sperm formation
Prader Willi and Angelman Syndrome
Linked to the same imprinted region on chromosome 15 some of the genes in the region are silenced on the egg or atleast one is silenced in the sperm
Prader Willi Syndrome
Learning difficulties short stature compulsive eating
Individuals are missing gene activity that normally comes from dad
Occurs when dads copy is missing or when there are two maternal copies
Angelman Syndrome
Learning difficulties speech problems seizures jerky movements and happy disposition
Individuals are missing gene activity that normally comes from the mum.
Occurs when mums copy is missing or there are two paternal copies
DNA methylation
Usually occurs at clusters of cytosine commonly found in promoter sequences
Methylation inhibits the gene (turns it off)
A Methyl group is added to the DNA base (cytosine) therefore RNA polymerase can’t attach and RNA can’t produced therefore certain proteins can’t be made
Once DNA is methylated it is turned off permanently
Eg stem cells ie heart cell
All cell bodies contain same DNA but all the genes on that DNA that don’t relate to produced heart cells will be methylated.
Within the forming of gametes the DNA is demethylated and cell becomes stem cell again
Histone Acetylation
DNA is wrapped tightly around histones (made up of amino acids most important being lysine)
How tightly it is wrapped determines gene expression (RNA polymerase can’t attach)
Acetyl group is added to lysine (found on tail of histone)
Changes structure of proteins loosening the DNA attached to it
Loosened DNA can now be transcribed
Unlike methylation, histones are constantly being acetylated and deacetylated
Polygenic Inheritance
Characteristic that is controlled by two or more genes
Bell shaped distribution curve
Skin Colour:
Determined by amount of melanin in skin
At least 4 genes are involved in melanin production with each gene having two alleles (one for production the other not)
Combination of these alleles determines the degree of pigmentation
aabbcc - fair skin
AaBbCc - medium skin colour
Also effected by environmental factors
What is epigenetics
Study of changes in organisms caused by modification of gene expression rather then change alteration of the genetic code itself
