Learning Outcomes
The phenotypic expression of genes depends on the interaction of genes and the environment (SU)
The Phenotypic Expresson of genes (and Epigenetics)
A cell does not express all the genes of its genome at the same time and at the same rate.
There are controls over which genes a cell expresses and how fast/often specific genes are transcribed.
Without this ability to regulate the expression of genes, all if the cells in your body would look and function in an identical way!
Coding vs Non-Coding DNA:
Much of an organism's genome consists of non-coding DNA. This is DNA that follows on from a stop codon but is before a start codon, thus, it's code it never read by the cell.
Gene Expression and Gene Regulation:
Gene Expression: Refers to the gene being transcribed into mRNA and translated into a protein
Gene Regulation: Refers to the processes within a cell that enable a gene to be expressed in specific cells at specific times.
How is gene regulation completed?
There are controls over which genes a cell expresses and how fast/often specific genes are transcribed.
Without this ability to regulate the expression of genes, all if the cells in your body would look and function in an identical way!
Coding vs Non-Coding DNA:
Much of an organism's genome consists of non-coding DNA. This is DNA that follows on from a stop codon but is before a start codon, thus, it's code it never read by the cell.
Gene Expression and Gene Regulation:
Gene Expression: Refers to the gene being transcribed into mRNA and translated into a protein
Gene Regulation: Refers to the processes within a cell that enable a gene to be expressed in specific cells at specific times.
How is gene regulation completed?
- DNA methylation: a methyl group attaches to some bases to prevent transcription. A common example is X-inactivation in female mammals, in which one of our X-chromosomes is turned off in each cell.
- Imprinting: a gene is imprinted (silenced) due to the attachment of methyl or acetyl groups to the histones, effecting coiling of chromosomes.
- Products of other genes: some genes code for proteins that will regulate the expression of other genes! These proteins are called regulatory proteins.
Environmental Influences on Gene Expression
Phenotypic Expression of genes can be influenced by the environment.
The epigenome consists of chemical compounds that modify the genome and affect gene expression.
Influence of the environment on the Epigenome
E.g. The Himilayan Rabbit
The rabbit has a white body with black ears, nose, feet and tail. If you apply a cold pack to a patch of white fur on the rabbit for a few weeks, the rabbit will begin to grow black hair beneath the pack. It appears as though the heat prevents the expression of the gene for the black pigment, so black fur only grows on the rabbits coolest areas. The same has been seen in Siamese cats.
The epigenome consists of chemical compounds that modify the genome and affect gene expression.
Influence of the environment on the Epigenome
E.g. The Himilayan Rabbit
The rabbit has a white body with black ears, nose, feet and tail. If you apply a cold pack to a patch of white fur on the rabbit for a few weeks, the rabbit will begin to grow black hair beneath the pack. It appears as though the heat prevents the expression of the gene for the black pigment, so black fur only grows on the rabbits coolest areas. The same has been seen in Siamese cats.
https://www.science.org.au/curious/epigenetics
Human Health:
Epigenetics can affect phenotype:
Human Health:
- The old saying, "you are what you eat". Our exposure to toxins, chemicals, radiation, etc may be turning on or off very important genes and causing illnesses.
- Studies have shown that stress and diet effect the way our genes are expressed.
- In mice, a diet high in methyl groups resulted in obesity in mice and a higher diabetes and cancer risk.
Epigenetics can affect phenotype:
- Epigenetics is the study of inheritable (but reversible) changes in gene expression in the absence of changes to the DNA sequence.
- Epi means "above", this is because the factors effecting gene expression are "above" DNA. They are able to activate and deactivate genes without altering the DNA in any way.
- Example:
- Stress and diet has the ability to alter phenotype by altering chromatin structure.
- Acetyl group added to chromatin will typically promote transcription (gene "ON")
- Methyl group added to chromatin will typically reduce transcription (gene "OFF")
- The chromatin structure is inherited, so it effects offspring.
- But because it is not DNA sequence alteration, it is not a mutation and therefore it can be "reversed" via changes to environment.
- Stress and diet has the ability to alter phenotype by altering chromatin structure.
- Examples of environmental conditions which alter human epigenomes:
- smoking
- over-eating
- malnutrition
- exposure to heavy metals
- electromagnetic radiation
- emotional trauma or stress
Now you should
Complete Question Set 4.1
Explore some of the resources on today's seqta lesson.
Explore some of the resources on today's seqta lesson.