Unit 2 - 9. Mutations

Question 1

Mutation

Answer 1

• a permanent change in the nucleotide sequence or arrangement of DNA in the genome which is not caused by recombination and which can be transmitted from parent to offspring.
• Can be chromosomal or individual genes

Question 2

Polymorphism

Answer 2

• multiple alleles for a normal phenotype at a locus, where at least 2 alleles appear with frequency greater than 1%
• Ex: ABO blood type system

Question 3

Benefits of Mutation

Answer 3

1. Mutations are the source of all new genetic information; they provide variablity in a population
2. Mutations are the basis for evolution of a species
3. Mutations can be induced for the benefit of man

Question 4

Harmful effects of Mutations

Answer 4

1. Can result in disease

2. Can result in death

Question 5

Nucleotide Base Substitution (point mutation)

Answer 5

1. Missense mutation = substitution of one nucleotide base for another resulting in a triplet code for a different amino acid. Ex. Sickle cell anemia
2. Nonsense mutation = point mutation resulting in the formation of a premature stop codon
3. Sense mutation = point mutation in a stop codon changing it to an amino acid resulting in a longer peptide chain
4. RNA splicing mutation = point mutation interferes with RNA splicing site, blocking or creating new sites. Ex. Tay-Sachs disease

Question 6

Deletions and Insertions

Answer 6

1. Frame Shift Mutation = change in reading frame of DNA code by deleting or inserting a number of bases that is not a multiple of 3. Ex: Hemoglobin Wayne
2. Codon Deletions and Insertions = number of bases involved is a multiple of 3. Ex: Cystic Fibrosis
3. Gene Deletions/Duplications = often due to unequal crossing over; from misalignment of sister chromatides resulting in one chromosome missing a gene and the other with 2. Ex: Growth Hormone deficiency & alpha-Thalasemia
4. Allelic Expansion = addition of repeated tri-nucleotide sequences which causes an increase in the size of the gene. Ex: Fragile X syndrome & Huntington

Question 7

Effects of Mutation

Answer 7

1. Some mutations will be silent, since they code for the same amino acid
2. most mutations are recessive and will not be immediately expressed
3. some mutations code for unimportant changes
4. some mutations can lead to disease and have severe effects, some do not let the individual survive to reproductive age.

Question 8

Epigenetics

Answer 8

• study of heritable changes in gene expression that are not due to changes in DNA sequence
• involves reversible chemical modifications of DNA or histones (methylation = silence)

Question 9

Genomic Imprinting

Answer 9

• epigenetics - expression of gene depends on whether it is inherited from mother or father
• occurs when copies of maternal/paternal are lost / duplicated
  Ex: prader-willi syndrome = 2 chromosome #15 of maternal
  Angelman syndrome = 2 paternal chromosome #15

Question 10

4 major types of mutagens

Answer 10

1. Ionizing radiation = cause DNA to be in an excited, unstable, more chemically reactive salt (free radicals). Ex: X-rays, radioactive isotopes, cosmic rays
2. Ultraviolet irradiation = UV causes formation of thymine dimers(T=T) in the skin
3. Chemicals = can change structure of DNA and its ability to replicate. Via: Base analogs = resemble nucleotides, fit into DNA; Chemical modification = can change one base into another; Bind to DNA = intercalating agents = distort shape
4. Viruses = can intergrate their DNA into host genome inducing changes in host cell DNA

Question 11

DNA Repair Mechanisms

Answer 11

1. Proof-reading mechanism of DNA polymerase

2. Photoreactivation (activated by light)

Question 12

The Ames Test

Answer 12

• > 90% of chemicals known to be carcinogens are positive in this test
• uses his- salmonella bacteria, if a chemical/mutagen is added to the plate and the bacteria grows, it is because a mutation occured changing his- to his+ meaning the chemical is positive = a mutagen