Mutations

R S T U V X Y Z → K L R S T U V X Y Z

An insertion adds new material. Here, K and L are added to the original sequence.

R S T U V X Y Z → S T U V X Y: R and Z were removed. That's a deletion.

R S T U V X Y Z → R S T V X Y Z: U was removed. That's a deletion.

R S T U V X Y Z → R U T S V X Y Z: S and U swapped positions. Nothing was added.

Somatic cell mutations are generally not passed to offspring. Gamete mutations are usually passed to offspring.

Somatic (body) cell mutations affect only that individual's cells or tissues. Gamete (sperm or egg) mutations can be inherited by offspring.

Somatic cell mutations occur in cells that give rise to gametes. Gamete mutations occur in cells that result in apoptosis.: Germ cells, not somatic cells, give rise to gametes. Apoptosis happens in both kinds of cells.

Somatic cell mutations are maintained in the gene pool. Gamete mutations are expelled from the gene pool.: Somatic mutations aren't inherited, so they don't enter the gene pool.

Somatic cell mutations will not be expressed by the individual that contains the mutation. Gamete mutations will be expressed by the individual.: A mutation in any cell can be expressed by the individual.

Insertion

A sequence of bases (TATC) is added to the original gene sequence, so this is an insertion.

Deletion: No bases are removed from the original sequence.

Substitution: No bases are swapped for others; new bases are added.

Translocation: Translocation moves part of one chromosome to another. That isn't shown here.

The mutation occurred in somatic cells.

Asbestos damages body (somatic) cells, such as lung cells. Mutations in somatic cells are not passed to offspring.

The mutation occurred in gametic cells.: Mutations in gametes (sex cells) can be passed to offspring.

The mutation is recessive.: Recessive mutations can still be passed to offspring.

The mutation is sex-linked.: Sex-linked mutations can be passed to offspring.

Substitution

One DNA base is replaced by another, changing one codon and the amino acid from His to Pro. This is a substitution.

Insertion: No extra base is added to the sequence.

Translocation: No chromosome segment moves to a different chromosome.

Deletion: No base is removed; one base is replaced.

0%

Somatic cells are body cells, not gametes. A mutation confined to a somatic cell is not passed to offspring.

100%: Only a mutation transmitted through gametes could be inherited; a somatic mutation is not.

75%: Inheritance percentages from a cross do not apply because the mutation is not in gametes.

25%: A somatic-cell mutation has no direct route into offspring.

The second cell from the left and the cell farthest to the right

The second and fifth cells both show unequal separation of homologous chromosome pairs, which is nondisjunction.

Mutation 2, because the deletion causes a frameshift and changes the downstream amino acid sequence.

Mutation 2 causes a frameshift: AAA GGC CAC becomes AAG GCC AC, changing the amino acid sequence. Naming Mutation 2 or explaining the frameshift earns one point; a complete response earns two.

Translocation

The exchange of genetic information between chromosome 9 and chromosome 22 is an example of a translocation mutation.

Deletion: A deletion mutation would show an overall loss of genetic information.

Insertion: An insertion mutation would show an overall increase in genetic information.

Nondisjunction: Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during meiosis.

Original DNA: 3’ CGT TAT GCT T 5’ Mutated DNA: 3’ CGT GTA TGC TT 5’ Mutation description: A single base is inserted, which could result in a protein with a different amino acid sequence and shape.

A frameshift mutation changes the reading frame of the DNA being transcribed. The inserted base shifts every downstream codon and may produce a protein with a completely different amino acid sequence and shape.

Original DNA: 3’ CGT TAT GCT T 5’ Mutated DNA: 3’ CTC GTA TTG T 5’ Mutation description: A section of DNA breaks away and reattaches to the chromosome in the reverse order without affecting the resulting protein.: This describes an inversion mutation, where a stretch of bases appears in reverse order.

Original DNA: 3’ CGT TAT GCT T 5’ Mutated DNA: 3’ CGT AAT GCT T 5’ Mutation description: One base is substituted for another, which could result in a stop codon and a protein with a different amino acid sequence and shape.: A substitution can produce an early stop codon, but it is not a frameshift mutation.

Original DNA: 3’ CGT TAT GCT T 5’ Mutated DNA: 3’ CGT TAA GCT T 5’ Mutation description: A single base is changed and codes for the same amino acid without affecting the resulting protein.: This describes a silent mutation, not a frameshift mutation.

Substitution

A substitution occurs when one base is replaced by a different base and the length of the DNA sequence is unchanged. Here, C was replaced by T.

Deletion: A deletion removes a base without replacing it, producing a shorter DNA sequence.

Insertion: An insertion adds a new base without removing one, producing a longer DNA sequence.

Translocation: A translocation moves an entire section of a chromosome to a different chromosome.