SC.912.L.14.6 Mutations
You need to know that mutations in the DNA sequence may or may not result in phenotypic change
You need to know that mutations in gametes may result in phenotypic changes in offspring.
Any change to an organism’s genetic material is called a MUTATION.
All mutations fall into two basic categories: GENE Mutations and CHROMOSOMAL Mutations
GENE MUTATIONS
A gene mutation is a change in the sequence of the DNA that makes up a single a gene. Changes in a gene’s DNA sequence can change proteins by altering their amino acid sequences, which may directly affect one’s phenotype.
Mutations that change a single base pair are called point mutations. These types of mutations usually occur due to errors during DNA replication. Cells copy their DNA during the S phase of interphase.
Point mutations include:
Substitution: switch of a base pair
Insertion: gain of a base pair
Deletion: loss of a base pair
Silent Mutations: The mutation produces a new codon that still codes for the same amino acid, this mutation would not have an observable effect on the organism's phenotype.
Missense mutations: The change results in a codon that codes for a different amino acid and usually have an observable effect on the organism's phenotype.
Nonsense mutation: The mutation produces a stop codon, which stops translation to stop before the protein was finished producing a defective protein
Insertion and deletion are known as frame shift mutations because they shift the "reading frame" of the genetic message and they can change every amino acid that follows the point of the mutation.
CHROMOSOMAL MUTATIONS
Chromosomal mutations change the structure or the number of the chromosomes.
Chromosomal mutations that change the structure of the chromosome of occur due to mistakes during DNA replication of crossing over. Deletion, Duplication, Inversion and Translocation
Chromosomal mutations that change the number of chromosomes occur due to mistakes during meiosis. Chromosomes may fail to separate during gamete production (Nondisjunction) resulting in gametes with too many or too few chromosomes.
Nondisjunction in Meiosis I (anaphase I) Homologous chromosomes do not separate
Nondisjunction in Meiosis II (anaphase II) Sister chromatids do not separate
Causes of Mutations
1. Environmental factors: ultraviolet radiation, exposure to chemicals, exposure to radiation from a nuclear power plant or X rays
Expose to radiation from a nuclear power plant can affect the egg cells of a woman causing a mutation that can be passed on to her children
2. Heredity: Mutations in DNA can be passed down from a parent to a child
Mutations appear in the phenotype of an organism if the mutation is recessive and is present in both copies of the diploid gene; for example, example Cystic fibrosis, Tay-Sachs disease
Mutations appear in the phenotype of an organism if the mutation is dominant and is present in one of the two copies of the diploid gene; for example Huntington disease
Pierced ears or scars are NOT passed on to children, because only changes to the DNA in the mother’s eggs cells are passed on to her children.
3. Mistakes during DNA replication, or mistakes during Meiosis: DNA polymerase can make a mistake in matching nucleotides during replication
A Change in a single base pair generally occurs during DNA replication, during the S Phase of interphase
A mRNA codon that reads C-C-C is miscopied, so the new codons reads C-C-G, both code for proline so there will be no difference in the resulting protein because the new codon codes for the same amino acid
The genetic code is a code for proteins but an organism can make other molecules like lipids, carbohydrates, and nucleic acids because enzymes can be used as tools to build other types of molecules.