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Genetics > Genetics Chapter 19.1-19.4 > Flashcards

Genetics Chapter 19.1-19.4 Flashcards

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1
Q

What is a Mutation?
Pros and Cons

A

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

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2
Q

Chromosomal Alteration

A

Chromosomal changes in structure or number affect multiple genes

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3
Q

Gene mutation

A

Gene mutation usually affects only one gene

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4
Q

Point mutation

A

is a base substitution

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5
Q

Transition

A

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

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6
Q

Transversion

A

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

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7
Q

Nucleotide Deletions

A

removes at least one nucleotide in a gene.

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8
Q

Nucleotide Insertions

A

addition of one or more nucleotides

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9
Q

What is the genetic code?

A

3 base sequence is called a codon
Genetic code is redundant

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10
Q

Missense mutation

A

changes amino acid sequence
A single change in amino acid sequence

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11
Q

Silent mutation

A

no change in amino acid sequence

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12
Q

Frameshift mutation

A

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

Can shift the reading frame

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13
Q

Nonsense mutation

A

codon→stop codon
Results in an early termination of protein

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14
Q

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

A
  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
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15
Q

Promoter

A

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

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16
Q

Neutral mutation

A

no change protein function

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17
Q

Deleterious mutation

A

lowers the chance of survival and reproduction

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18
Q

Lethal mutation

A

results in death of the cell or organism

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19
Q

Beneficial mutation

A

enhances the survival or reproductive success

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20
Q

Conditional mutation

A

is one that affects the phenotype only under specific conditions

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21
Q

Suppressor Mutations

A

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

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22
Q

Reversion

A

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

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23
Q

IntrAgenic Suppressors

A

The second mutation is in the same gene as the first

RESTORES function of the mutated gene

24
Q

IntErgenic Suppressors

A

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

25
Q

Different types of intErgenic suppressors

A
  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
26
Q

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

A

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

27
Q

Two common reasons for position effects

A
  1. Movement to a position near regulatory sequences
  2. Movement to a heterochromatic region
28
Q

Germline mutations

A

are inherited in next generation

29
Q

Somatic mutations

A

create a mosaic individual

30
Q

Random mutation therapy

A

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

31
Q

What causes mutations?

A

Induced mutations
Spontaneous mutations

32
Q

Induced mutations

A

Caused by environmental agents- mutagens

33
Q

Spontaneous mutations

A

Result from abnormalities in cellular/biological processes

34
Q

Deamination(spontaneous)

A
  • 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
35
Q

Deamination of 5-methylcytosine - spontaneous

A

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

36
Q

Depurination(of cytosine - spontaneous)

A

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

37
Q

Tautomeric Shifts (spontaneous)

A
  • 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
38
Q

Oxidative stress and DNA damage - spontaneous

A
  1. Reactive oxygen species (ROS): generated by normal metabolism
  2. Oxidative stress: is an imbalance between synthesis and destruction of ROS
39
Q

Reactive oxygen species (ROS)

A

generated by normal metabolism

40
Q

Oxidative stress

A

is an imbalance between synthesis and destruction of ROS

41
Q

Effects of Mutagens

A
  • Threatens the integrity of the genetic code→mutations
  • Risks to human’s health
  • Inherited mutations
  • Cancer
  • Neurodegenerative diseases
  • Calcified as chemical or physical mutations
42
Q

Induced Mutations

A
  • 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
43
Q

Two types of Physical Mutagens

A

Ionizing radiation
Non Ionizing radiation

44
Q

Ionizing radiation

A

​​- 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

45
Q

Ionizing radiation can cause

A

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

46
Q

Non Ionizing radiation

A
  • Includes UV light
  • Has less energy
  • Cannot penetrate deeply
  • Causes the formation of crosslinked thymine dimers
47
Q

Four types of Chemical Mutagens

A

Base modifiers
Base analogs
Alkylating agents
Intercalating agents

48
Q

Base modifiers

A

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

49
Q

Base analogs

A

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

50
Q

Alkylating agents

A

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)

51
Q

Intercalating agents

A

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

52
Q

Trinucleotide Repeat Expansion Disorders - spontaneous

A

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)

53
Q

Two unusual features of TNRE disorders:

A
  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
54
Q

Mutation Rate

A

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

55
Q

Ames test

A

evaluate mutagenicity

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

56
Q

Steps of Ames test

A
  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

Genetics (5 decks)

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