Section 8 - 20 Gene Expression Flashcards
What is a mutation?
Any change to the quantity or the structure of the DNA of an organism.
What is a gene mutation?
Any change to one or more nucleotide bases, or any rearrangement of the bases, in DNA
What is a substitution mutation?
When a nucleotide in a section of DNA molecule is replaced by another nucleotide that has a different base.
What are three possible consequences of substitution mutation?
- formation of one of the three stop codons that mark the end of a polypeptide chain. - stopped prematurely
- Formation of a codon for different amino acid meaning structure of polypeptide produced would differ in single amino acid. - not correct shape or function
- formation of a different codon but one that produces a codon for the same amino acid - degenerate nature.
What is a deletion mutation?
The loss of a nucleotide base from a DNA sequence
What does a deletion mutation cause?
A frame shift
a reading frame that contains every three letters of the code has been shifted to the left by one letter.
What is addition mutation?
The extra base becomes inserted in the sequence.
Cause a frame shift to the right.
What is duplication mutation?
One or more bases are repeated.
Produces a frame shift to the right.
What is an inversion mutation?
Group of bases become separated from the DNA sequence and rejoin at the same position but in the inverse order.
Base sequence is therefore reversed and affects the amino acid sequence that results.
What is a translocation mutation?
Group of bases become separated from the DNA sequence on one chromosome and become inserted into the DNA sequence of a different chromosome.
Often having significant effects on gene expression leading to an abnormal phenotype.
These effects include the development of certain forms of cancer and also reduced fertility.
Typically how many natural mutations occur?
One or two mutations per 100000 genes per generation.
What two outside factors affect the basic mutation rate?
- mutagenic agents
- mutagens
What is included in the terms mutagenic agents or mutagens?
- high energy ionising radiation
- chemicals
What is cell differentiation?
The process why which each cell develops into a specialised structure suited to the role that it will carry out.
Another name for a fertilised egg
Zygote
What are totipotent cells?
A fertilised egg which has the ability to give rise to all types of cells.
What do controlling factors do?
ensure that genes for proteins are not expressed.
In what ways do genes prevented from expressing themselves?
- preventing transcription and so preventing the production of mRNA
- preventing translation
At what point can cells no longer specialise into another?
Once cells have matured and specialised they can no longer develop into other cells.
What are stem cells?
Undifferentiated dividing cells that occur in adult animal tissues and need to be constantly replaced.
What are stem cells capable of?
They have the ability to divide to form an identical copy of themselves in a process called self-renewal.
Where do stem cells originate?
- embryonic stem cells
- umbilical cord blood stem cells
- placental stem cells
- adult stem cells
Where are totipotent stem cells found?
In the early embryo.
What are pluripotent stems cells?
Found in embryos
Can differentiate into almost any type of cell.

