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BIOL 2320 - Genetics > Gene Mutations > Flashcards

Gene Mutations Flashcards

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1
Q

How do mutations occur?

A

randomly

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2
Q

How often do mutations occur?

A

rarely

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3
Q

How do spontaneous mutations occur?

A

mutations that arise mainly through errors in DNA replication (without exposure to mutagens)

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4
Q

How do induced mutations arise?

A

through the exposure to mutagens (often called carcinogens)

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5
Q

When are mutations heritable?

A

When they occur in germ-line cells they will end up in sperm or egg and be passed on

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6
Q

When are mutations not heritable?

A

when they occur in somatic cells

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7
Q

How do mutations change the DNA?

A

Substitute
add
delete
one or more DNA base pairs

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8
Q

Where do point mutations occur?

A

at specific, identifiable position in a gene
or
a specific location in the genome

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9
Q

Describe base-pair substitution mutations

A

the replacement of one nucleotide base pair by another

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10
Q

What are the 3 types of base-pair substitution mutations?

A

synonymous
missense
nonsense

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11
Q

Describe synonymous mutations

A

a base-pair change that does not alter the result of the amino acid

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12
Q

Why do synonymous mutations occur?

A

because of the redundancy of the genetic code and the wobble position

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13
Q

Describe missense mutations

A

a base-pair change that results in an amino acid change in the protein

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14
Q

Describe nonsense mutations

A

base-pair change that creates a stop codon instead of a regular codon for an amino acid

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15
Q

Describe frameshift mutations

A

when there is an insertion or deletion of one or more base pairs in the coding region of a gene that changes the reading frame of the message

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16
Q

Where does the frameshift mutation occur? What does this change cause?

A

in the mRNA

it alters the reading frame of the message

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17
Q

What are the consequences of frameshift mutations?

A

premature stop codons can be produced

the wrong amino acid sequence can be produced starting from the point of mutation

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18
Q

Describe mutations in regulatory regions/noncoding regions

A

mutations that change the amount of protein produced by a gene but not the amino acid sequence

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19
Q

T or F: regulatory mutations change the amino acid sequence

A

false! they change the amount of protein produced by a gene

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20
Q

What regions can regulatory mutations affect?

A

promoters
introns
regions that code for 5’-UTR and 3’-UTR

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21
Q

Describe promoter mutations

A

mutations that alter consensus sequence nucleotides of promoters

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22
Q

What are the consequences of promoter mutations?

A

interference of transcription initiation:

mild-moderate reductions in transcription levels

stopping transcription

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23
Q

Describe splicing mutations

A

alterations of nucleotides (specific sequences) at either end of an intron

24
Q

What are the consequences of splicing mutations?

A

Splicing errors

production of mutant proteins because introns aren’t spliced

25
Q

What are the consequences of splice site mutations?

A

can dramatically change mRNA transcript

can cause large insertion or deletions in mature mRNA that may or may not be in frame

result in non-functioning proteins

26
Q

What do splicing mutations often result in?

A

non-functioning proteins

27
Q

Describe cryptic splice sites and how they form

A

new splice sites that can replace or compete with authentic splice sites formed by base-pair substitution during mRNA processing

28
Q

Give an example of cryptic splice sites

A

A base-pair substitution that changes G to A at position 110 of human beta-globin intron 1 creates an AG splice site which leaves 19 additional nucleotides in the mature mRNA

29
Q

Describe polyadenylation mutations

A

alteration of the signal sequence for the addition of the Poly-A tail at the 3’ end of eukaryotic mRNA which causes blocking of 3’ processing of mRNA

30
Q

What consequences do polyadenylation mutations have?

A

they reduce the amount of protein produced:

reduce ability of mRNA to leave nucleus for translation

make mRNA more vulnerable to degradation before translation (parts of mRNA may be lost)

31
Q

Describe a null mutation

A

When a mutation within a gene causes loss of function and produces no functional gene product

32
Q

Describe leaky mutations

A

A mutation within a gene that causes partial loss of function and produces a partially functional gene product

33
Q

Describe a silent mutation

A

a mutation within a gene that produces a normally functioning gene product

34
Q

What does the severity of the phenotype of a leaky mutation depend on?

A

the level of activity of the gene product

35
Q

What type of mutations will result in a null mutation product?

A 
promoter mutations
frameshift mutations
nonsense mutations
splicing mutations
missense mutations (less common)
36
Q

What type of mutation will cause leaky mutations?

A

missense mutations

37
Q

What type of mutation will cause silent mutations?

A

synonymous mutations

38
Q

What are the terms dominant and recessive based on?

A

phenotypes

39
Q

What determines the dominance of one allele over another?

A

the protein product of the alleles

40
Q

What are phenotypes the result of?

A

the activities of the protein products of the alleles of a gene

41
Q

Are mutations of haplosufficient genes dominant or recessive?

A

recessive

42
Q

What does a wild-type allele (R) produce in haplosufficient genes?

A

an active enzyme (50 units)

43
Q

How many units does an active enzyme produced by a wild-type allele (R) in haplosufficient genes have?

A

50

44
Q

What does a mutant allele (r) in haplosufficient genes produce?

A

no active enzyme (0 units)

45
Q

How many units does an inactive enzyme produced by a mutant allele (r) in haplosufficient genes have?

A

0

46
Q

How many units of enzyme activity are required to produce a wild-type phenotype in haplosufficient genes?

A

40+

47
Q

How many functional copies of a gene is enough for normal function in heterozygotes with haplosufficient genes?

A

one

remember that Rr will display the dominant phenotype - only required one functional copy (R)

48
Q

Are mutations of haploINsufficient genes dominant or recessive?

A

dominant

49
Q

What does allele T1 in haploinsufficient genes produce?

A

an active enzyme (10 units)

50
Q

How many units does an active enzyme from T1 allele in haploinsufficient genes produce?

A

10 units

51
Q

What does the mutant allele T12 in haploinsufficient genes produce?

A

a less active enzyme (5 units)

52
Q

How many units does the less active enzyme produced by mutant allele T2 in haploinsufficient genes have?

A

5 units

53
Q

How many units of enzyme activity is required to produce the wild-type phenotype in haploinsufficient genes?

A

18+ (only T1T1 individuals are WT)

54
Q

Using the T1 and T2 key, what genotype would individuals with haploinsufficient genes have to have to express the WT phenotype?

A

T1T1 (homozygous) because the mutation (T2) is dominant in haploinsufficient genes

55
Q

Using the T1 and T2 key, what genotype would individuals with haploinsufficient genes have to have to express the mutant phenotype?

A

either T1T2 or T2T2 because neither produces enough enzyme to make the WT phenotype

56
Q

In haploinsufficient genes, how many functional copies of a gene are required for normal functioning (the production of the WT phenotype)?

A

More than 1

BIOL 2320 - Genetics (12 decks)

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