Genetics Chapter 19.1-19.4

Question 1

What is a Mutation?
Pros and Cons

Answer 1

Mutations: heritable change in the genetic material
Pros: provide allelic variations
foundation for evolutionary change
Cons: Can be detrimental if they result in an allele that functions more poorly than the original

Question 2

Chromosomal Alteration

Answer 2

Chromosomal changes in structure or number affect multiple genes

Question 3

Gene mutation

Answer 3

Gene mutation usually affects only one gene

Question 4

Point mutation

Answer 4

is a base substitution

Question 5

Transition

Answer 5

is a change between Cs and Ts or between As and Gs

Question 6

Transversion

Answer 6

is a change of a pyrimidine (C, T) to a purine (A, G) or vice versa

Question 7

Nucleotide Deletions

Answer 7

removes at least one nucleotide in a gene.

Question 8

Nucleotide Insertions

Answer 8

addition of one or more nucleotides

Question 9

What is the genetic code?

Answer 9

3 base sequence is called a codon
Genetic code is redundant

Question 10

Missense mutation

Answer 10

changes amino acid sequence
A single change in amino acid sequence

Question 11

Silent mutation

Answer 11

no change in amino acid sequence

Question 12

Frameshift mutation

Answer 12

addition or deletion of nucleotides in multiples of one or two but not three (the size of one codon)

Can shift the reading frame

Question 13

Nonsense mutation

Answer 13

codon→stop codon
Results in an early termination of protein

Question 14

Explain how a mutation in non-coding DNA can affect the expression of a gene.

Answer 14

1. Promoter
   Up promoter mutations: increase transcription
   Down promoter mutations: decrease transcription
2. Splice junctions in eukaryotes
3. 5’ and 3’ UTR – alter stability of RNA, translation
4. Regulatory element– disrupt proper regulation of gene expression

Question 15

Promoter

Answer 15

Up promoter mutations: increase transcription
Down promoter mutations: decrease transcription

Question 16

Neutral mutation

Answer 16

no change protein function

Question 17

Deleterious mutation

Answer 17

lowers the chance of survival and reproduction

Question 18

Lethal mutation

Answer 18

results in death of the cell or organism

Question 19

Beneficial mutation

Answer 19

enhances the survival or reproductive success

Question 20

Conditional mutation

Answer 20

is one that affects the phenotype only under specific conditions

Question 21

Suppressor Mutations

Answer 21

a second mutation that affects the phenotypic expression of a first mutation

Question 22

Reversion

Answer 22

A REVERSING mutation or reversion changes a mutant allele→wild-type

Question 23

IntrAgenic Suppressors

Answer 23

The second mutation is in the same gene as the first

RESTORES function of the mutated gene

Question 24

IntErgenic Suppressors

Answer 24

The second mutation is in a DIFFERENT GENE than the first

Relieve the effect of a mutation in one gene by a mutation somewhere else within a genome

Question 25

Different types of intErgenic suppressors

Answer 25

1. Redundant function: Second protein may take on the role of the first 2. Proteins may act in the same cellular pathway 3. Polypeptides may be subunits of the same multimeric protein 4. Mutation of a transcription factor can cause it to activate expression of another gene that can compensate for the loss of function

Question 26

What is it called when gene expression can be altered if a gene is RELOCATED?

Answer 26

POSITION EFFECT Can result in either an increase or decrease in expression Changes in chromosome structure can affect gene expression Double stranded breaks can occur within a gene

Question 27

Two common reasons for position effects

Answer 27

1. Movement to a position near regulatory sequences 2. Movement to a heterochromatic region

Question 28

Germline mutations

Answer 28

are inherited in next generation

Question 29

Somatic mutations

Answer 29

create a mosaic individual

Question 30

Random mutation therapy

Answer 30

Mutations occur in any gene or piece of DNA randomly (although there may be hot spots) Do not need selection for the mutation to occur Growth conditions may then select for most adapted organism

Question 31

What causes mutations?

Answer 31

Induced mutations Spontaneous mutations

Question 32

Induced mutations

Answer 32

Caused by environmental agents- mutagens

Question 33

Spontaneous mutations

Answer 33

Result from abnormalities in cellular/biological processes

Question 34

Deamination(spontaneous)

Answer 34

- Removal of an AMINO group from the cytosine base - By removing amino group, the base changes from a cytosine to a uracil - DNA repair enzymes recognized uracil as an INAPPROPRIATE BASE in DNA, therefore, they REMOVE IT

Question 35

Deamination of 5-methylcytosine - spontaneous

Answer 35

5-methylcytosine are deaminated to thymine→repair enzymes don’t repair this

Question 36

Depurination(of cytosine - spontaneous)

Answer 36

Removal of a purine (guanine or adenine) from the DNA

Question 37

Tautomeric Shifts (spontaneous)

Answer 37

- A temporary change in base structure - To cause a mutation it must occur immediately prior to DNA replication - These rare forms promote AC and GT base pairs

Question 38

Oxidative stress and DNA damage - spontaneous

Answer 38

1. Reactive oxygen species (ROS): generated by normal metabolism 2. Oxidative stress: is an imbalance between synthesis and destruction of ROS

Question 39

Reactive oxygen species (ROS)

Answer 39

generated by normal metabolism

Question 40

Oxidative stress

Answer 40

is an imbalance between synthesis and destruction of ROS

Question 41

Effects of Mutagens

Answer 41

- Threatens the integrity of the genetic code→mutations - Risks to human’s health - Inherited mutations - Cancer - Neurodegenerative diseases - Calcified as chemical or physical mutations

Question 42

Induced Mutations

Answer 42

- Mutagens can permanently alter the structure of DNA - often involved in the development of human cancers - Induced mutations can be classified as chemical or physical mutagens

Question 43

Two types of Physical Mutagens

Answer 43

Ionizing radiation Non Ionizing radiation

Question 44

Ionizing radiation

Answer 44

​​- Includes X-rays and gamma rays - Has short wavelength and high energy - Can penetrate deeply into biological materials - Creates chemically reactive molecules termed free radicals

Question 45

Ionizing radiation can cause

Answer 45

Base deletions Single nicks in DNA strands Cross-linking Oxidized bases Chromosomal breaks

Question 46

Non Ionizing radiation

Answer 46

- Includes UV light - Has less energy - Cannot penetrate deeply - Causes the formation of crosslinked thymine dimers

Question 47

Four types of Chemical Mutagens

Answer 47

Base modifiers Base analogs Alkylating agents Intercalating agents

Question 48

Base modifiers

Answer 48

induced and covalently modify the structure of a nucleotide Ex: nitrous oxide

Question 49

Base analogs

Answer 49

incorporated into daughter strands during DNA replication For example, 5- bromouracil is a thymine analogue 5BU undergoes a tautomeric shift and base pairs with G

Question 50

Alkylating agents

Answer 50

mutagens that disrupt pairing by alkylating bases within the DNA Methyl or ethyl groups are covalently attached to the bases Examples: Nitrogen mustard and ethyl methanesulfonate (EMS)

Question 51

Intercalating agents

Answer 51

flat planar structures that intercalate themselves into the double helix distorts the helical structure Results in single-nucleotide additions and/or deletions resulting in frameshifts Examples: Ethidium bromide and Proflavin

Question 52

Trinucleotide Repeat Expansion Disorders - spontaneous

Answer 52

In TRNE disorders, the length of a trinucleotide repeat increases above a certain critical size Example: The trinucleotide repeat CAG in Huntington’s Disease If a gene in coding region, TRNE adds glutamines to amino acid sequences A key aspect of TNRE is that the triplet repeat can form a hairpin (or stem-loop)

Question 53

Two unusual features of TNRE disorders:

Answer 53

1. The severity of the disease tends to worsen in future generations - called anticipation 2. Severity depends on whether it is inherited from the father or mother

Question 54

Mutation Rate

Answer 54

Probability that a gene will be altered by a new mutation Expressed as the number of new mutations in a given gene per cell generation Rate is not constant Ames test used to measure rate

Question 55

Ames test

Answer 55

evaluate mutagenicity The point of the test: test is to see if an agent increases the reversion rate

Question 56

Steps of Ames test

Answer 56

1. Mix a Salmonella strain (histidine negative (his-neg)) with either rat liver extract (negative control) or rat liver extract + mutagen 2. Spread cells on agar plates that do not contain histidine 3.Cells that grow obtained a reversion mutation in their histidine gene