Chapter 18 Part 1

Question 1

Mutation

Answer 1

Inherited change in the DNA sequence

Extra: They are essential to the study of genetics and are useful in many other biological fields

Question 2

Somatic Mutation

Answer 2

Mutations in somatic tissues – not the reproductive organs like the ovary and testes

Mutations are passed on by mitosis, and can produce clones of this mutation

This type of mutation is known to increase with age

Question 3

Germ-line Mutation

Answer 3

Mutations – in the gametes or reproductive tissues

This type of mutation can be passed on to future generations, producing offspring that carry that mutation in all their somatic and germ-line cells

Question 4

Gene Mutation

Answer 4

Mutation that affects a single gene or locus

Question 5

Spontaneous Mutations

Answer 5

Mutations that arise from natural changes in DNA structure or from error of replication

Question 6

Induced Mutation

Answer 6

Those mutations that arouse from changes caused by environmental chemicals or radiation

Question 7

Tautomeric Shift

Answer 7

The positions of protons – hydrogen atoms – in DNA bases change

“Each of the four DNA bases are in dynamic equilibrium, although one form is much more common than the other”

Cytosine rare form can bind with Adenine common form

Thymine common form can bind with Guanine rare form

Question 8

Wobble –Mis-pairing

Answer 8

The normal protonated form of the nitrogenous bases are able to pair because of flexibility in the DNA helical structure

Thymine can wobble with Guanine

Cytosine can wobble with Adenine

Question 9

Incorporates Errors

Answer 9

When a base substitution causes a mis-paired base to be incorporates into a newly synthesized nucleotide chain

1. DNA Wild Type
   TTCG
   AAGC
2. The DNA strands separate for DNA replication
   TTCG Thymine on the original strand pairs with Guanine through wobble
   AGGC –> Incorporated errorTTCG –> wild type
   AAGC
3. At the end of the next round of replication, the guanosine nucleotide pairs with cytosine, leading to a transition mutation

TTCG –> Wild type
AAGC

TCCG –> Mutant
AGGC

Question 10

Replicated Error

Answer 10

The permanent base pair mutation that aroused because of an incorporated mistake

Question 11

Stand Slippage

Answer 11

Small insertions and deletions can arise spontaneously in crossing over and replication

Slipping of the template and newly synthesized strands in replication in which one of the strands loops out from the other and nucleotides are inserted or deleted on the newly synthesized strand

The shorter strand that loops out has an insertion
The longer strand that loops out will have a deletion

Question 12

Misaligned pairing

Answer 12

If homologous chromosomes misalign during cross over, one crossover products contains an insertion and the other contains a deletion

Question 13

Depurination

Answer 13

The loss of a purine base from a nucleotide
Depurination results when the covalent bond connecting the purines to the 1’-carbon atom the deoxyribose sugar breaks, producing an apuritic site

In the absence of base-pairing constraints, an incorrect nucleotide – most often adenine – is incorporated into the newly synthesized DNA strand opposite to the apuritic site… leading to incorporated errors

Question 14

Deamination

Answer 14

The loss of an amino group – NH2 – from a base

Ex…Cytosine can be converted to uracil
A form of Transition mutation

Ex….
5mC –> Thymine

Question 15

Mutagen

Answer 15

Any environmental agent that significantly increases the rate of mutation above the spontaneous rate is called a mutagen

Question 16

Transition Mutations

Answer 16

A purine changes to a purine
A pyrimidine changes to a pyrimidine

Question 17

Transversion

Answer 17

A purine changes to a pyrimidine
A pyrimidine changes to a purine

Question 18

Base Analogs

Answer 18

Chemicals with structure similar to those of any of the four stranded nitrogenous bases of DNA

DNA polymerase cannot distinguish these analogs from the stranded bases, so if base analogs are present during replication, they may be incorporates into newly synthesized DNA molecules

For example…5-bromouracil is an analog of thymine – it has the same structure as thymine except that it has a broken – Br atom on the 5-carbon atom instead of a methyl group… so instead of pairing with adenine…it pairs with guanine

Same thing can happen with 2-aminopurine which is analog to Adenine, which pairs wrongly with cytosine

Question 19

Pyrimidine dimers

Answer 19

Pyrimidine bases readily absorb UV light, which causes chemical bonds to form between adjacent pyrimidine molecules on the same strand of DNA, creating pyrimidine dimers

Question 20

SOS system

Answer 20

overcome blocks caused by pyrimidine dimers

Question 21

Carcinogen

Answer 21

cancer-causing substances

Question 22

Ames Test

Answer 22

Is based on the principle that both cancer and mutations results from damage to the DNA –> a solution to help resolve cancer

Question 23

Transposable Elements

Answer 23

DNA sequence capable of moving from one site to another within the genome through a mechanism that differs from that of homologous recombination – are often a cause of mutations

Question 24

Suppressor Mutation

Answer 24

A mutation that hides or suppresses the effect of another mutation

“A suppressor mutation is a second mutation that alleviates or reverts the phenotypic effects of an already existing mutation in a process defined synthetic rescue” - https://en.wikipedia.org/wiki/Suppressor_mutation

–> Let us say that a mutation cause the amino acid arginine to change to serine
–> Let us say that another mutation – suppressor mutant – changes serine to lysine
Since lysine and arginine share similar properties –> the mutant these type has no effect on the gene or the phenotype

Question 25

Intragenic

Answer 25

Suppressor mutations on the same genes as original mutation

Question 26

Intergenic

Answer 26

Suppressor mutations on a different gene as the original mutation

Question 27

In-frame mutations

Answer 27

An insertion or a deletion that alter the reading frame and may change many codons
–> multiples of 3

Question 28

Loss-of-functional mutation

Answer 28

Partial or complete absence of gene product function

usually recessive – requires two copies in a diploid organism to see a phenotype

Question 29

Gain-of-functional mutation

Answer 29

Gene product has a new function

Usually dominant – one copy – in a diploid organism – produces a phenotype

Question 30

Conditional Mutation

Answer 30

Phenotype seen under certain conditions
– elevated temperatures

Question 31

Lethal mutation

Answer 31

Causes premature death