Mutations

Mutations

Mutations

• We all make mistakes, don’t we? Sometimes, cells make mistakes when they copy their DNA.

• Mutations are mistakes in DNA sequencing, and they can affect the genetic information passed to offspring. 

• Sometimes the mistakes are so small that they are 

  never noticed.

• These are called silent mutations.

Mutations

• Mutations can fall into two different categories – gene mutations and chromosome mutations.

• Gene mutations occur when 1 or more nucleotide bases are changed.

• Chromosome mutations occur when pieces/parts of chromosomes are changed. They have much larger effects.

Gene Mutations: Point Mutations

• Point Mutations are mutations that involve only one single nucleotide.

• Ex: Substitution: a gene mutation that

   occurs when one mutation is substituted for another nucleotide.

Gene Mutations: Frameshift Mutations

• Frameshift Mutations are mutations that occur when a nucleotide is added or deleted and it causes a shift in how the codons are read; this results in one or more wrong amino acids being added.

• Ex: Deletion: a gene mutation in which a nucleotide is lost or deleted.

• Ex: Insertion: a gene mutation in which a nucleotide is added.

Chromosomal Mutations

• Another type of mutation is a chromosomal mutation, where the structure or numbers of chromosomes change. 

• The structure of a chromosome can change if a part of a chromosome is broken off or lost during the process of mitosis or meiosis. 

Types of Chromosomal Mutations

• A broken part can sometimes reattach to a sister chromatid and cause deletion of genetic information in one chromatid and duplication of genetic information on the other.

• If the broken part reattaches backwards, it is called an inversion.

• The broken part may also attach to another chromosome, which is called translocation.

If a chromosome does not separate correctly, this is called nondisjunction, and a gamete will have an extra or a missing chromosome.

Meiosis vs. Mitosis

• When mutations occur during the process of meiosis, that mutation can be passed on to offspring. 

• The mutation becomes part of the offspring’s DNA and will be found in almost every cell. 

• This mutation can then be passed on to the next generation. 

• Existing genetic disorders are passed on to offspring when the defective gene becomes part of the gamete formed during meiosis.

• Example: Sickle Cell Anemia - caused by a single substitution in a gene that forms the protein hemoglobin. Because of the substitution, the wrong amino acid is added and the resulting hemoglobin protein is shaped differently and does not function as well.

Mitosis vs. Meiosis

• When mutations occur during mitosis, they usually happen during an organism’s lifetime. 

• Most mutations occur during the process of mitosis when the DNA is being copied and a mistake occurs – when the mistake isn’t repaired, it can lead to cellular malfunctions. 

• They affect the individual but aren’t passed to offspring.

• A mutagen is an external agent that can change DNA, such as radiation or some chemicals.

• A common result of mutations is cancer, and mutagens that are linked to cancer are called carcinogen. 

• Examples: excessive UV light exposure, radiation, tobacco, and chemical pesticides.

Multiple Choice

Why are insertion and deletion (frameshift) mutations so harmful?

• They change all of the codons from the mutation on down the line, which changes the amino acid sequence
• They insert things that an organism doesn't need.
• They often delete things that organisms need.
• Insertion and deletions are not any more harmful than substitution mutations.

Multiple Choice

Which of the following would result in a frameshift mutation?

• Insertions only
• Substitution only
• Deletion only
• Insertions and Deletions

Multiple Choice

What mutation has occurred here? 
T-G-A-C-C-A
T-G-A-G-C-A

• Substitution
• Deletion
• Insertion
• Frameshift 

Multiple Choice

In order for offspring to get a genetic mutation, the mutation must occur in what type of cell?

• Cells with no nucleus.

• Any body cell after birth.

• Cells with no cell wall or cell membrane.

• Cells like eggs or sperm cells that are undergoing reproduction.

Multiple Choice

A frameshift mutation where a nucleotide base

is removed from the DNA sequence.

• Deletion Mutation

• Substitution Mutation

• Translocation

• Silent Mutation

Multiple Choice

A frameshift mutation where a nucleotide base is added

to the DNA sequence

• Insertion Mutation

• Deletion Mutation

• Substitution Mutation

• Chromosomal Mutation

Multiple Choice

Part of a chromosome is repeated

• Gene Mutation

• Point Mutation

• Deletion Mutation

• Duplication Mutation

Multiple Choice

Part of one chromosome is transported and attached

to a non-homologous chromosome

• Inversion Mutation

• Translocation Mutation

• Duplication Mutation

• Point Mutation

Multiple Choice

Failure of homologous chromosomes

to separate during meiosis.

Results in gametes with either one extra or one missing chromosome.

• Translocation

• Nondisjunction

• Replication

• Transcription

Multiple Choice

Condition caused by nondisjunction at pair 21 during meiosis.

Individuals have an extra chromosome

at pair 21, or a total of 47 chromosomes.

Also called Trisomy 21.

• Cystic Fibrosis

• Translocation

• Hemophilia

• Down Syndrome

Multiple Choice

A point mutation where DNA adenine (A)

is replaced by thymine (T) resulting in a single amino acid change during translation(affects blood cell

shape and function)

• Encephelitis

• Hemophilia

• Sickle Cell Anemia

• Influenza

Multiple Choice

A nucleotide base is inserted or deleted shifting the entire DNA sequence. Entire protein will be changed.

• Substitution Mutation

• Silent Mutation

• Frameshift Mutation

• Translocation

Multiple Choice

A point mutation where one nucleotide base replaces an original nucleotide base

• Inversion Mutation

• Chromosomal Mutation

• Translocation

• Substitution Mutation

Multiple Choice

One nucleotide base is changed so only one amino acid

is affected

• Substitution Mutation

• Point Mutation

• Translocation

• Inverse Mutation

Multiple Choice

A change in a gene, group of genes or chromosome that results in a change in the proteins

• Replication

• Mutations

• Translation

• Transcription