Genes & Phenotypic Expression Flashcards
Chapter 1.5
What are phenotypic characteristics?
Physical factors expressed from genes, controlled by the gene pairs of homologous chromosomes.
What two key parts play a role in what genes are expressed?
Cell differentiation and environmental conditions.
What is cell differentiation?
Cells all begin as identical clones, able to become any type of specialised cell. Cells of certain types will express more genes suited to their purpose. Thus, all types of cells have significant differences in their internal structures, and these are derived from the types of proteins these cells produce.
What is the relationship between phenotype and genotype?
Phenotype = Genotype + Environmental factors
What is gene expression?
When a gene synthesises a protein.
What is DNA methylation?
A process in which a methyl group is added to the DNA strand, usually occurring at the cytosine base. It does not alter the DNA sequence, but can influence gene expression.
What impact can methylation have on protein synthesis?
It inhibits RNA polymerase from binding to the promoter region(s), consequently preventing transcription.
What occurs after methylation?
Genes typically retain their methyl groups when cell division occurs and thus the pattern of methylation can be passed on to daughter cells.
What is a promoter sequence?
A region of DNA that is not transcribed, but contributes to the transcription of a gene. It is where RNA polymerase initially binds to initiate transcription.
Describe transcription factors.
Known as activators, these bind to DNA and activate or increase the rate of transcription, whereas others, called repressors, bind to DNA to slow or stop transcription.
How does the binding of a repressor factor silence transcription?
It inhibits RNA polymerase from binding to the promoter region.
What does the binding of activator proteins do?
Binding to their respective base sequences stimulates gene expression.
What is histone modification?
The acetylation (modification) of histone proteins causes the chromatin to decondense, resulting in loose packing of the histone proteins. This allows RNA polymerase to bind to the DNA and the genes can be expressed (proteins are made).
What happens when deacetylation of histone proteins occur?
It causes the chromatin to condense, resulting in more tightly packed histone proteins. Thus, RNA polymerase is unable to bind to the DNA and transcription can no longer occur - this means genes are not expressed.
What is epigenetics?
The study of changes to the DNA that occur after cell differentiation. These are differences in how gene expression occurs; the sequence of DNA does not undergo change, and neither are these mutations. Examples include histone modification or methylation of the DNA sequence.
What happens if certain genes are not expressed?
It prevents the production of specific proteins from occurring, which can prove detrimental to the health of the organism.
What are examples of epigenetics?
The wrapping of histones or methylation of the DNA sequence; these are NOT mutations.
What are the two types of STEM cells?
Pluripotent and multipotent.
What is cell differentiation derived from?
The regulation of gene expression; in some cells, certain genes are ‘switched on or off’.
