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BIOL*1090 > Week 4 > Flashcards

Week 4 Flashcards

Allele variation, DNA structure, and mutations

1
Q

What is the wild type allele?

A

The most common allele for a trait

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2
Q

How are wild type alleles often represented?

A

With a superscript +

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3
Q

Any allele other than the wild type is considered __________.

A

Mutant

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4
Q

What is a polymorphism?

A

The presence of two or more variant forms of a specific DNA sequence/allele that affect the phenotype of different individuals.

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5
Q

What must be true for an allele to be considered a polymorphism?

A

The allele/trait must appear at appreciable frequencies (at least 1%) in a population to be considered a polymorphism

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6
Q

T or F: Different mutations in a gene can cause the same disorder

A

True

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7
Q

T or F: Different mutations in a gene can cause different phenotypes

A

True

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8
Q

What do recessive alleles almost always involve?

A

A mutation in a gene that results in at lease some loss of protein function

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9
Q

Why do phenotypic mutations rarely occur for heterozygous individuals?

A

Because one “good copy” of the gene is sufficient to make the protein required for the “normal” biological process to occur

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10
Q

What are the two types of mutations?

A
  • Complete loss of function
  • Partial loss of function
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11
Q

What type of allele causes a complete loss of function?

A

A null allele

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12
Q

What type of allele causes a partial loss of function?

A

A hypomorphic allele (aka neomorphic)

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13
Q

What are the three types of dominance?

A
  • Complete
  • Incomplete
  • Codominant
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14
Q

What is complete dominance?

A

The phenotype of a heterozygote dominant for the trait is the same as a homozygote dominant for the trait

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15
Q

What are two ways in which complete dominance from an allele can alter function?

A
  • Gain of a new function
  • Complete loss of a function
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16
Q

What is incomplete dominance?

A

The phenotype of a heterozygote falls in between the phenotypes of two homozygotes

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17
Q

What is the ratio of inheritance for incomplete dominance when both parents are heterozygous?

A

1:2:1 (dominant:”in between”:recessive)

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18
Q

What is Codominance?

A

The phenotype of a heterozygote includes the phenotypes of both homozygotes

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19
Q

What is meant by a multi-allelic system?

A

More than two allele variations exist at a population level, and different individuals in the population may have different pairs of these alleles (ex. blood types)

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20
Q

What are two additional factors at a single locus that can affect phenotype?

A
  • Penatrance
  • Expressivity
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21
Q

What does penetrance describe?

A

The percentage of individuals having a particular genotype that express the expected phenotype

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22
Q

What is complete penetrance?

A

100% of individuals with a certain genotype express the expected phenotype

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23
Q

What is incomplete penetrance?

A

Individuals do not express a trait even though they have the genotype

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24
Q

How can penetrance be calculated?

A

By dividing the total number of individuals with the expected phenotype by the total number of individuals with the specific genotype but don’t necessarily express the phenotype

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25
Q

What is expressivity?

A

The degree to which a character is expressed within a given genotype

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26
Q

What are three potential explanations for incomplete penetrance and variable expressivity?

A
  • Environmental factors
  • Epigenetics
  • Maternal age
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27
Q

What are epigenetics?

A

Changes in gene expression, but not due to mutations

28
Q

What is a temperature sensitive allele?

A

An allele whose product is only functional at certain temperatures

29
Q

What are the three components of a nucleotide?

A

A sugar, a nitrogenous base, and a phosphate group

30
Q

What is the main difference between ribose and deoxyribose?

A

Ribose sugar contains a hydroxyl group on the 2’ carbon and deoxyribose does not

31
Q

What are the two types of nitrogenous bases?

A
  • Purines
  • Pyrimidines
32
Q

How does the structure of purines and pyrimidines differ?

A
  • Purines: a six-member ring attached to a five member ring
  • Pyrimidines: a six member ring
33
Q

What are the two types of purines?

A
  • Adenine
  • Guanine
34
Q

What are the two types of pyrimidines in DNA?

A
  • Cytosine
  • Thymine
35
Q

What are the two types of pyrimidines in RNA?

A
  • Cytosine
  • Uracil
36
Q

Which nitrogenous bases pair in DNA?

A
  • Adenine and Thymine
  • Guanine and Cytosine
37
Q

Which nitrogenous bases pair in RNA?

A
  • Adenine and Uracil
  • Guanine and Cytosine
38
Q

How are the polynucleotide strands arranged in DNA?

A

Antiparallel to each other

39
Q

What is meant when it is said that polynucleotides in DNA run antiparallel to each other?

A

They run in opposite directions (one strand runs 5’ to 3’ and the other runs 3’ to 5’)

40
Q

How many hydrogen bonds hols T and A together?

A

Two

41
Q

How many hydrogen bonds hold C and G together?

A

Three

42
Q

How are the two polynucleotide strands held together in DNA?

A

Hydrogen bonds between complementary nitrogenous base pairs

43
Q

How are adjoining nucleotides connected in polynucleotide strands?

A

A phosphodiester linkage connects the 5’ phosphate group of one nucleotide to the 3’ hydroxyl group of the other

44
Q

What are changes in DNA that result in a new allele called?

A

Mutations/variants

45
Q

Why can mutations be beneficial?

A

They are the source of genetic variation and provide the raw material for evolution

46
Q

Why might it be useful to identify mutant genes that alter development?

A

They are useful for identifying the function of that gene

47
Q

Which type of genetic mutation can be passed to members of the next generation?

A

Germ-line mutations

48
Q

Where do somatic mutations occur?

A

Nonreproductive cells

49
Q

Where do germ-line mutations occur?

A

In cells that give rise to gametes

50
Q

What are the three main categories of gene mutations?

A
  • Base substitutions/point mutations
  • Insertions and deletions
  • Expanding nucleotide repeats
51
Q

What are the two types of base substitution/point mutations?

A
  • Transition
  • Transversion
52
Q

What are the two types of insertions and deletions?

A
  • Frameshift mutations
  • In-frame insertions and deletions
53
Q

What is the result of an expanding nucleotide repeat?

A

Increase in the number of copies of a set of nucleotides

54
Q

What is a transition mutation?

A
  • When one purine replaces another purine (ex. A replaces G)
  • When one pyrimidine replaces another pyrimidine (ex. T replaces C)
55
Q

What is a transversion mutation?

A
  • When a purine replaces a pyrimidine (ex. A replaces C)
  • When a pyrimidine replaces a purine (ex. T replaces A)
56
Q

What is a frameshift mutation?

A

When an insertion or deletion alters the reading frame and therefore the codons

57
Q

What is an in-frame insertion or deletion?

A

When the insertion or deletion of nucleotides occurs in groups of three, so the reading frame and codons are not affected

58
Q

T or F: A frameshift due to insertion or deletion will not cause a stop codon to be read.

A

False. Frameshifts may result in stop codons being read after the mutation.

59
Q

What causes an expanding nucleotide repeat mutation?

A
  • A hairpin forms on a newly synthesized strand of DNA, causing part of the template strand to be replicated twice
  • When it is used as the template for replication, the resulting DNA will have those additional copies
60
Q

What is a forward mutation?

A

Mutation causing a wild type allele to become a mutant allele

61
Q

What is a reverse mutation?

A

Mutation causing a mutant allele to become a wild type allele

62
Q

What is a neutral mutation?

A

Mutation that causes no change in function

63
Q

What is a missense mutation?

A

When the new codon encodes for a different
amino acid as the original (change in amino acid sequence)

64
Q

What is a nonsense mutation?

A

When the new codon encodes for a stop codon/nonsense codon (premature termination of translation)

65
Q

What is a silent mutation?

A

When the new codon encodes for the same
amino acid as the original (no change in the amino acid sequence)

BIOL*1090 (15 decks)

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