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General Biology I > lecture 12: mutation > Flashcards

lecture 12: mutation Flashcards

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1
Q

What is a mutation?

A

Permanent change in a cell’s genome

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2
Q

Are mutations goal-oriented?

A

No, they are random in nature and any DNA sequence can be affected

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3
Q

What do mutations result from? (2)

A
  1. DNA damage

2. Mistakes made during cell division

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4
Q

What induces mutations? (2)

A

Induced by mutagens

  1. Physical agents
  2. Chemical agents
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5
Q

What are examples of mutagens that induce mutations?

A

Natural metabolism, UV light, H2O2

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6
Q

What are the 3 possible effects of mutation on organisms?

A
  1. Beneficial
  2. Neutral
  3. Harmful
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7
Q

What are the two scales of mutations?

A
  1. Gene Mutations

2. Chromosome Mutations

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8
Q

Characteristics of gene mutations? (2)

A
  • Small scale

- Involve one gene

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9
Q

Characteristics of chromosome mutations?

A
  • Large scale

- Involve several genes

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10
Q

What do gene mutations cause? (3)

A
  1. Base pair substitutions
  2. Base pair additions or deletions
  3. Segment duplications or deletions
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11
Q

What do chromosome mutations cause? (2)

A
  1. Changes to chromosome structure

2. Changes to chromosome number

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12
Q

Describe a gene mutation/small-scale mutation

A

1 original DNA —> Error in replication (base-pair mismatch) —> Cell division: one daughter cell have the right, original template & other will have a mutant (different mRNA and polypeptide produced)

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13
Q

What are the 4 types of structural changes to chromosomes (large-scale mutation)?

A
  1. Deletion: removes a chromosomal segment
  2. Duplication: repeats a segment
  3. Inversion: reverses a segment within a chromosome
  4. Translocation: moves a segment from one chromosome to a nonhomologous chromosomes

—> Changes whole regions of chromosomes which contain several genes

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14
Q

Does a karyotype allow us to observe small-scale mutations (gene mutations)?

A

No, only large-scale mutations (chromosome mutations)

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15
Q

Three categories of effect of mutations on organisms based on their fitness

A
  1. Beneficial mutations: increases fitness of organism
  2. Neutral mutations: do not affect their fitness
  3. Deleterious mutations (FREQUENT): decrease the fitness of the organism
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16
Q

most small-scale mutations are … or …

A

neutral or deleterious

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17
Q

Large-scale mutations are almost always…

A

deleterious

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18
Q

SOMETIMES mutations results in…

A

beneficial

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19
Q

What is the main effect of mutation?

A
  • Ultimate source of genetic and trait variation in all populations
  • Fuel for evolution and speciation
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20
Q

Are mutations considered as diseases?

A

No, if there weren’t mutations, there would not have any difference in traits

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21
Q

What important characteristic of genes result from mutation?

A

Alleles or genes —> different versions of one gene

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22
Q

How are mutations the foundation of variation in traits in a population?

A

Various alleles —> Various genotypes —> Expression of different genotypes results in different phenotypes (traits)

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23
Q

What else usually contributes to our phenotype?

A

Environment

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24
Q

What are the 2 types of mistakes in mammals and what do they result in?

A
  1. Mistakes in mitosis —> somatic mutations

2. Mistakes in meiosis —> germ-line mutations

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25
Q

Characteristics of germ-line mutation? (3)

A
  • Entire organism carries the mutation
  • Half of their gametes carry the mutation
  • Mutation can be passed on to offsprings
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26
Q

Characteristics of somatic cell mutations (4)

A
  • Only of patch of affected area
  • None of gametes carry the mutation
  • Produces genetic mosaic: populations of cells within the body contain different genotypes
  • Usually not passed on to offspring
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27
Q

What are the 3 mistakes a cell can make during cell division?

A
  1. DNA replication
  2. Crossing over
  3. Anaphase
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28
Q

Describe a mistake made during DNA replication

A

Point mutations can change sequence of a gene (base-pair mismatch) —> change sequence of the polypeptide produced (mutant) —> affect its function

29
Q

What might be the effect (neutral, harmful, or beneficial) of a single nucleotide substitution?

A

Harmful or neutral (if it’s a different amino acid, but same codon)

30
Q

What might be the effect (neutral, harmful, or beneficial) of a single nucleotide deletion?

A

Base-pair removed —> change reading scheme —> different codon when read —> Harmful

31
Q

What might be the effect (neutral, harmful, or beneficial) of a single nucleotide addition?

A

Base pair added —> change reading scheme and codon read —> Harmful

32
Q

Describe mistake made during crossing over

A

Crossing over has to be done with precision that is reciprocal (need same region of gene exchanged from both chromosomes) —> If aligned incorrectly —> Unequal crossing over —> Can duplicate or delete regions within a gene

33
Q

What do mistakes during anaphase cause?

A

Nondisjuction: mistake where chromosomes fail to be separated correctly —> results in aneuploid daughter cells with abnormal chromosome number —> nondisjuction during meiosis results in aneuploid gametes —> aneuploid gamete can produce aneuploid zygote after fertilization

34
Q

What is aneuploid?

A

Have abnormal chromosome numbers

35
Q

Will outcome differ if mistake happens in meiosis I vs when it happens in meiosis II?

A

Yes in meiosis I —> 2 daughter cells will have n+1 chromosome (one additional) & 2 other daughter cells will have n-1 chromosomes (missing one)

In meiosis II —> 1 has n+1, another n-1 and the 2 others have normal number (n)

36
Q

What do aneuploidies/aneuploid zygotes usually lead to?

A

Majority of miscarriages

- Do not lead to viable offspring in humans as they do not complete development

37
Q

2 types of aneuploidies?

A
  1. Trisomy: condition in which somatic cells contain 3 copies of one chromosome
  2. Monosomy: condition in which somatic cells contain only 1 of a chromosome pair
38
Q

What is Trisomy 21 (Down’s Syndrome)?

A

Example of autosomal aneuploidy

- 3 copies of chromosome 21

39
Q

What is Monosomy X (Turner’s Syndrome)

A

Example of sex chromosome aneuploidy

  • Born with 1 X chromosome —> female
  • Only monosomy observed in humans that gives rise to live births
40
Q

2 types of sex chromosome aneuploidies

A
  1. Nondisjunction during egg development

2. Nondisjunction during sperm development

41
Q

Which nondisjuction mistake occur most often?

A
  • Trisomy 21 = most observed type of trisomy —> much more common in the smaller chromosomes (13-22)
  • Most aneuploidies (other than trisomy 21) are sex chromosome aneuploidies
42
Q

Autosomal aneuploidy vs Sex chromosome aneuploidy

A

Sex chromosome aneuploidies = much less severe consequences on development and survival

43
Q

What makes nondisjunction occur?

A

Accidents, not genetic predisposition

44
Q

What are 2 patterns in the occurence of nondisjunction?

A
  1. Maternal errors (due to error in egg vs error in sperm): accounts for most incidences of trisomy
  2. Maternal age (46-48): important factor in occurrence of trisomies
45
Q

3 types of autosomal aneuploidies

A
  1. trisomy 21
  2. trisomy 18
  3. trisomy 13
46
Q

Characteristics of trisomy 21 (Down Syndrome)?

A
  • 1/800 frequency of # of live births

- Mental retardation, abnormal pattern of palm creases, slanted eyes, flattened face, short stature, early death

47
Q

4 types of sex chromosome aneuploidies

A
  • XXY
  • XYY
  • XXX
  • XO
    More flexibility
48
Q

What is cancer?

A

General term for family of diseases caused by cells that are growing in an uncontrolled fashion and form dangerous masses called tumors

  • Complex disease that affect array of organs
  • Highly variable genetic causes resulting from mutation
  • 90% do not involve mutation —> passed on to offsprings
49
Q

Characteristics of tumors

A

Use nutriments and space needed by normal cells & disrupt function of normal tissues and organs giving rise to disease and death

50
Q

2 types of tumors

A
  1. Benign: self-limited in growth, do not invade or metastasize, must be monitored as they can become malignant
  2. Malignant: cancerous, cells divide quickly and are invasive, can matastasize
51
Q

Cancel cells display… (2)

A
  1. Uncontrolled cell division

2. Unlimited cell division

52
Q

Why do cancer cells divide abnormally?

A
  • Bc they have defective cell communication and cell cycle control system
53
Q

Why do cancer cells have unlimited capacity for cell division? (2)

A

Bc they evade protective mechanisms that usually limit cell division:

  1. Senescence (aging
  2. Apoptosis (programmed cell death)
54
Q

Normal cells only divide if… (3)

A
  1. Nutrients are available
  2. Growth factors are present
  3. Substratum (solid-support) for attachment is present (anchorage dependence —> cells anchor to surface
55
Q

Normal cells stop dividing if…

A

they come into contact with other cells which limits cell density to a single layer (density-dependent inhibition)

56
Q

Cell division defects in cancer cells do not produce single-layer of cells, they produce…

A

clumps of overlapping cells

57
Q

Why do cancer cells lose normal limitations during cell division?

A

They ignore physical/chemical cues

58
Q

What causes a cell to become cancerous?

A

Defects caused y accumulation of mutations that affect activity of proteins involved in:

  1. Cell cycle control
  2. Cell communication
  3. Cell senescence
  4. Apoptosis
  5. DNA repair (no repair = increases number of mutation rate in all the above)
59
Q

How many mutations are needed for normal cells to become cancer cell?

A

Typically several mutations + many different combinations of defects

60
Q

2 main types of mutations all activities of proteins

A
  1. Make go proteins overactive

2. Make stop proteins underactive

61
Q

What are go proteins? (4)

A
  • Products of proto-oncogenes
  • Function in progression of cell cycle (go): tell cells to divide
  • Promote cancer when activity is increased (overactive): too much division
  • Transferred by cancer viruses
62
Q

What are stop proteins?

A
  • Products of tumor suppressor genes
  • Function in stopping cell cycle or promoting senescence or apoptosis
  • Promote cancer when activity is decreased (underactive): don’t stop division so more mutations
63
Q

How does cancer develop?

A

Requires accumulation of SEVERAL mutations in a cell that converts normal genes into abnormal versions that produce abnormal go and stop proteins

64
Q

Why is cancer prominent in later ages?

A

More time for more mutations

65
Q

What are the 4 possible treatments of cancer?

A
  1. Surgery: if localized
  2. Radiation: if localized, destroy cancel cells to make them nonfunctional, make cancer cells lose their ability to repair DNA
  3. Chemotherapy: for metastatic tumours, damage all actively diving cells, lot of side effects
  4. Targeted/Personalized Therapies: specific for a individual tumour
66
Q

What is “metastasize”?

A

Cancer cells spread in respiratory system, blood vessels and to other parts of the body —> form secondary tumours

67
Q

What are some side effects of chemotherapy and why are there side effects?

A

Nausea: affecting the lining of digestive system
Immune suppression: less production of white blood cells
Hair loss: affect the production of hair follicle
—> Because all dividing cells are destroyed so the cells that NEED dividing would be affected too

68
Q

What are targeted/personalized therapies?

A

The goal of cancer treatment as there is no cure for cancer

  • Best option
  • Find treatments that only target cancer with less damage possible to healthy cells

General Biology I (19 decks)

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