Chromosomal and Gene Mutations
Proteins and Mutations:
Some _____________________________ carry out functions within the cells of an organism.
Other proteins are ____________________________ out of the cell for other purposes.
Still other proteins are used as activators or repressors, turning ________________________________ on or off.
Therefore, a change in a cell’s _______________________ could have dramatic effects on the cell’s structure or
function.
Changes in the ___________________________ can change the proteins synthesized by the cell.
A random change in the sequence of nucleotides in DNA is called a __________________________________.
Some mutations have little or no effect on the organism, others are ___________________________ and very few
are ________________________________________________.
There are two types f mutations:
1. ____________________________________________________
2. ____________________________________________________
Chromosomal Mutations:
Chromosomal mutations are changes in the _________________________________________ of a chromosome.
Gene Mutations:
Gene mutations are errors that occur within _____________________________________________________ in a
chromosome.
Gene mutations can involve a single nucleotide or they can affect sections of DNA that include many nucleotides.
1. The deletion or addition of nucleotides that disrupts codons is called a
_____________________________________.
Because mRNA is read in _____________________ (three-base sections) during translation, an addition or deletion
of nucleotides can alter the sequence of bases, or reading frame, of the genetic message.
Analyze the following frameshift mutation:
What are the codons in the original reading frame?
What are the codons in the shifted reading frame?
Recall what happens when a strand of mRNA is transcribed from DNA.
What might happen if one base is deleted from the DNA?
The _____________________________________________________________________ would also be affected.
Because each mRNA codon corresponds to an ______________________________, altering the codons may alter
the amino acid sequence.
The end result may be an entirely different ________________________ product. Frameshift mutations can have
an enormous impact on an organism’s
________________________________________________________________.
2. A change in only one nucleotide is a ____________________________________________________.
Because a point mutation affects a __________________________________________, it tends to be far less
disruptive than a frameshift mutation.
Some amino acids are coded for by more than one __________________________, and substitutions may simply
change one codon to another codon for the same amino acid.
For example:
CUU = _______________________________________
Any change in the third base: CUC, CUA, CUG
still codes for the amino acid ___________________________________________.
About ________________________________ of all substitution mutations produce no changes in proteins.
In the remaining________________________________ of point shift mutations, changed nucleotides cause a
different amino acid to be incorporated into a protein.
The resulting protein may function ______________________________________ or may be defective.
The following diagram shows a point shift mutation and how it changes the gene from normal hemoglobin
production to the production of sickle-cell hemoglobin, which in turn causes sickle-cell disease.
A third and very common point mutation occurs when a codon in the middle of a gene is changed to a
___________________________________________.
For example: UGC = Cysteine but UGA = Stop
When genes with this mutation go through protein synthesis, translation is halted before the amino acid chain is
completed.