Mod 6: Mutations (CQ1)

Question 1

Define mutations

Answer 1

A change in the base sequence of an organism’s DNA

Question 2

What causes a mutation?

Answer 2

• Mutagens
  -Cellular errors

Question 3

What are mutagens?

Answer 3

Environment agent that damages DNA (E.g, Chemicals, radiation, toxins)

Question 4

What are cellular errors?

Answer 4

Cell makes errors during cell division
- E.g, Chromosomal (whole chromosome) and point (point of chromosome)

Question 5

How is electromagnetic radiation a mutagen?

Answer 5

• UV light + X-rays + Gamma rays have high energy and cause mutations
• ER waves move through matter, give energy to atoms -> Atoms ‘hyped up’ by extra energy, causing them to vibrate & lose electrons -> Chemical bonds break -> Cell dies or live with mutated DNA

Question 6

What are 3 sources of electromagnetic radiation?

Answer 6

• Sun
• Radioactive elements
• Medical imaging machines

Question 7

How are chemicals a mutagen?

Answer 7

1. Accidentally incorporated into DNA, instead of proper nucleotide
2. Chemicals insert itself into DNA
3. Chemicals make gap in DNA

Question 8

What are naturally-occurring mutagens?

Answer 8

• Microbe: Mycotoxins are poisonous chemicals produced by fungi
• Plant: Cycasin is a mutagenic chemicals, found in the leaves of cycad plants
• Animal: Dimethylnitrosamine is produced in the stomach when nitrite is consumed

Question 9

What are point mutations?

Answer 9

• Only one nucleotide is changed
• Occur due to errors in DNA replication (Insertion, deletion, substitution)

Question 10

What are the effects of point mutations?

Answer 10

Base is inserted or deleted:
- Every codon after mutation is affected = Frameshift point mutation
Base is substituted:
- Mis-sense
- Non-sense
- Silent

Question 11

What is a Mis-sense mutation?

Answer 11

Substitution of one nucleotide, codon codes for a different amino acid

Question 12

What is a Non-sense mutation?

Answer 12

Substitution of one nucleotide, stop codon created (Prematurely stops growth of polypeptide)

Question 13

What is a Silent mutation?

Answer 13

Substitution of one nucleotide, codon codes for same amino acid

Question 14

What is an example of a point mutation?

Answer 14

Sickle Cell anaemia:
Genetic disorder where people have misshapen red blood cells
- Caused by substitution of single nucleotide
- Haemoglobin folds into abnormal shape -> Molecules clump together

Question 15

What is a chromosomal mutation?

Answer 15

A change in the arrangement or structure of a chromosome:
- Occur due to errors in cell division
- Crossing over during meiosis, increasing probability of error

Question 16

What are the types of chromosomal mutations?

Answer 16

1. Deletion -> Section breaks off & is lost
2. Inversion -> Section breaks off, flips around & reattaches
3. Translocation -> Section breaks off & sticks to a different chromosome
4. Duplication -> Section accidentally copied more than one
5. Nondisjunction -> Chromosomes don’t separate properly

Question 17

What are the effects of chromosomal mutations?

Answer 17

1. (All) If breakage occurs in middle of a gene, the gene will be destroyed
2. (Deletion, insertion, translocation) Genes are moved to a new place
3. (Duplication) Changes in the amount of proteins produced
4. (Nondisjunction) Aren’t so distinct

Question 18

What is an example of chromosomal mutation?

Answer 18

Down syndrome (trisomy 21):
- Genetic disorder where people have 3 copies of chromosome #21
- Due to nondisjunction during formation of gametes

Question 19

What is a Germ cell?

Answer 19

Any cell which can divide (by meiosis) to form sex cells -> Responsible for genes passed from parents to offsprings

Question 20

What is a Germ-line mutation?

Answer 20

Change in the DNA of a germ cell

Question 21

What are the effects of a germ-line mutation?

Answer 21

Mutated germ cell undergo meiosis to form a gamete which contains mutated DNA -> ALL OFFSPRINGS cells will have the mutations

Question 22

What is a somatic cell?

Answer 22

Any cell which forms the body tissue of the organism -> Only performs mitosis

Question 23

What are the effects of somatic mutations?

Answer 23

• Only affect daughter cells of mutated somatic cell:
  1. Offspring unaffected (Not inherited)
  2. Mutation CAN’T be passed onto offspring as a somatic cell can’t form a gamete
• How somatic mutation affects the organism depends on which genes are mutated

Question 24

What is an example of a somatic mutation?

Answer 24

Lung cancer:
A disease that results from uncontrolled cell growth in lungs –> Occur in somatic cell and will not be passed onto offspring

Question 25

What is coding DNA?

Answer 25

- DNA which codes for amino acid sequence of a protein - Effect on mutation in coding DNA depends on type of mutation

Question 26

What is an example of a mutation as a result of coding DNA?

Answer 26

Sickle cell anaemia

Question 27

What is non-coding DNA?

Answer 27

Doesn’t code for proteins: - Makes functional RNA (tRNA and rRNA) - Regulatory sequences (control amount of protein produced by coding DNA) - Repetitive sequence (Regions of DNA which are the same sequence repeated over & over)

Question 28

What are the effects of non-coding DNA?

Answer 28

- Mutation in functional RNA -> Protein synthesis may be affected - Mutation in regulatory sequence -> Gene transcription levels may change - Mutation in repetitive sequence -> Nothing happens

Question 29

What is exon shuffling?

Answer 29

Exons duplicating or moving to create new intron-exon sequence - Can from new gene & lead to a new protein with a new combination of functions

Question 30

What’s a gene pool?

Answer 30

Total collection of alleles for all genes in a pop. - Retains all genetic info of the pop., including number of genes, alleles & allele frequency - Dynamic = changes due to change in allele frequency or new alleles rise

Question 31

What is gene flow?

Answer 31

Movement of alleles between pop. due to movement of individual organisms

Question 32

What are factors affecting the gene pool?

Answer 32

- High gene flow between pop. -> Similar gene pools - Low gene flow or absent -> Gene pools are going to become increasingly different

Question 33

Define genetic drift

Answer 33

Random events (births, deaths) occurring within pop. which can lead to changes in gene pool

Question 34

How do mutations affect a population’s gene pool?

Answer 34

Source of new alleles, size of gene pool increase