Mutations Flashcards

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1
Q

How do mutations in the number of chromosomes arise?

A
  • Mutations in number of chromosomes can arise spontaneously by chromosome non- disjunction during meiosis.
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2
Q

What is non-disjunction?

A
  • Non disjunction is when chromosomes/ chromatids do not split/ separate equally during anaphase (so, cells produced won’t have the correct no of chromosomes.)

() - extra info for clarification.

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3
Q

True or False

Chromosome non-disjunction can only occur in meiosis I.

A
  • False.
  • Chromosome non-disjunction can occur in either meiosis I or meiosis II.
  • Meiosis I: either one/ all chromosomes don’t separate equally.
  • Meiosis II: either either one/ all chromatids don’t separate equally.
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4
Q

What are the 2 different effects that chromosome non-disjunction can have?

A
  • Changes in whole sets of chromosomes - polyploidy.
  • Changes in the number of individual chromosomes - aneuploidy.
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5
Q

When does polyploidy occur?

A
  • Polyploidy occurs when you have changes in whole sets of chromosomes.
  • Changes in whole sets of chromsomes occur when organisms have three/ more sets of chromosomes rather than the usual two.
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6
Q

Describe process that would lead to polyploidy (non-disjunction in meiosis I.)

A
  • Each homologous pair is doubled (due to DNA replication in interphase.)
  • Non disjunction in meiosis I (all chromosomes fail to separate equally.)
  • Normal division in meiosis 2, chromatids separate equally.
  • 4 gametes produced. 2, 2n, diploid gametes and 2 gametes with no chromosomes.
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7
Q

What would happen if a 2n gamete (produced by non-disjunction) fuses with a normal n gamete?

A
  • A triploid (3n) cell would be produced - rather than a diploid cell.
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8
Q

How does aneuploidy actually occur?

A
  • Changes in number of individual chromosomes.
  • Individual homolgous pairs of chromosomes fail to separate in meiosis.
  • Results in gamete hacing one more/ one fewer chromosome.
  • When zygote with one more/ less chromosome fuses with normal gamete, the zygote will have more/ fewer chromosomes than in body cells.
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9
Q

Describe process that would lead to aneuploidy (non-disjunction occuring in meiosis I.)

A
  • Each homologous pair is doubled (due to DNA replication in interphase.)
  • Non disjunction in meiosis I (one chromosome does not separate equally.)
  • Normal division in meiosis 2, chromatids separate equally.
  • 4 gametes produced: two n+1 haploid gametes with one additional chromosome AND two n-1 haploid gametes with one missing chromosome.
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10
Q

If chromosome non- disjunction occurs in meiosis I - leading to polyploidy, what issue happens during meiosis?

A
  • All chromosomes fail to separate equally (ie. one cell ends up with all the chromosomes/ other cell doesn’t contain any chromosomes after meiosis I.)

() - extra info for clarification.

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11
Q

If chromosome non- disjunction occurs in meiosis I - leading to aneuploidy, what issue happens during meiosis?

A
  • One chromosome doesn’t separate equally (one cell has two of same homologous pair and other cell doesn’t contain that specific homologous pair.)
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12
Q

If chromosome non- disjunction occurs in meiosis II - leading to polyploidy, what issue happens during meiosis?

A
  • All the chromatids don’t separate equally (4 gametes –> 2 have no chromosomes/ 2 have 2 copies of each chromosome.)
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13
Q

If chromosome non- disjunction occurs in meiosis II - leading to aneuploidy, what issue happens during meiosis?

A
  • One chromatid doesn’t separate equally.
  • 4 gametes –> two have 1 missing chromosome, 2 have normal number of chromosomes.)
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14
Q

What will happen when n+1 gamete fuses with n (normal gamete?)

A
  • Forms 2n+1 zygote (diploid.)
  • Resultant zygote will have 1 extra chromosome.
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15
Q

What do gene mutations involve?

A
  • Gene mutations involve a change to the base sequence of chromosomes.
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16
Q

What are the two different types of gene mutation (that we need to know for AS?)

A

1.) Base deletion
2.) Base substitution.

17
Q

How can gene mutations arise?

A
  • ## Gene mutation can arise spontaneously during DNA replication.
18
Q

What do “mutagenic agents” do?

A
  • Mutagenic agents can increase the rate of gene mutation.
19
Q

The genetic code is generate. What does this mean for gene mutations?

A
  • Means that not all BASE SUBSTITUIONS cause a change in the sequence of encoded amino acids.
20
Q

Give 2 different examples of mutagenic agents/ what do they do?

A

1.) High energy/ ionising radiation - disrupt structure of DNA.
2.) Carcinogens - interfere with transcription.

21
Q

What does a deletion mutation lead do?

A
  • Causes frame shift to the right (all of the bases move along one.)
  • This could result in a different polypeptide chain and a non-functioning protein.

() - extra info for clarification.

22
Q

True or False

Substitution mutation leads to frame-shift and has a huge impact.

A
  • False.
  • There is no frame-shift, only one codon is changed.
  • May not have impact due to genetic code = degenerate (ie. codon may still code for the same amino acid.)