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A-level Biology Year 1 > Mutations & Meiosis > Flashcards

Mutations & Meiosis Flashcards

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1
Q

What is a gene mutation?

A

A spontaneous change in the sequence of DNA bases in a gene, occurring during DNA replication.

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2
Q

Changes in order of DNA bases ->

A

-> changes order of amino acids -> changes position of R groups -> changes position of bonds -> changes tertiary structure -> changes active site (if an enzyme)

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3
Q

What are the different types of gene mutation?

A
  • Addition
  • Deletion
  • Substitution
    • Silent
    • Nonsense
    • Missense
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4
Q

What is an addition gene mutation?

A

When a new base or triplet is incorporated into the original DNA base sequence.
Causes a frame shift that changes the amino acid sequence.
If at start it can change whole protein or change the start codon so that it no longer starts
If at end it can have little effect unless is in the stop codon.

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5
Q

What is a deletion gene mutation?

A

When a base or triplet is deleted from the original DNA base sequence.
Causes a frame shift that changes the amino acid sequence.
If at start it can change whole protein or change the start codon so that it no longer starts
If at end it can have little effect unless is in the stop codon.

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6
Q

What are the different types of substitution gene mutations?

A
  • Silent
  • Nonsense
  • Missense
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7
Q

What is a silent (substitution) gene mutation?

A

As the genetic code is degenerate the new triplet simply codes for the same amino acid

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8
Q

What is a substitution gene mutation?

A

The replacement of a base or triplet with another. Chances to not cause a mutation due to degenerate genetic code.

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9
Q

What is a nonsense (substitution) gene mutation?

A

The change in the triplet causes a stop codon to be created early, which would result in a non-functioning protein.

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10
Q

What is a missense (substitution) gene mutation?

A

The change in the base or triplet codes for an alternative amino acid.

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11
Q

What is genetic diversity?

A

How much variation there is.
Arises because of differences in what genes are present in an organism and due to presence of different alleles of a gene

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12
Q

What causes variation?

A
  • Mutation via producing new alleles
  • Random assortment
  • Crossing over
  • Random fusion of gametes
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13
Q

What are the potential results of a mutation?

A

Mutation may be:
- Advantageous
- Neutral
- Disadvantageous

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14
Q

What are examples of mutagenic agents?

A
  • High energy radiation (X and gamma rays)
  • Bacteria & viruses
  • Certain chemicals
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15
Q

What are the chromosomal mutations?

A
  • Inversion
  • Duplication
  • Translocation
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16
Q

What is an inversion chromosomal mutation?

A

A section of the DNA is detached, rotated and then reattached at the same point in the gene.
Flips the order of amino acids in this section.

17
Q

What is an duplication chromosomal mutation?

A

One or more bases are repeated causing a frame shift, altering the amino acid sequence and many create a non-functioning protein.

18
Q

What is an translocation chromosomal mutation?

A

A group of bases from one chromosome becomes detached from one chromosome and attaches to another.
Leads to a significant alteration in not only that amino acid sequence but the entire phenotype of the organism.
Can lead to cancer and other genetic disorders.

19
Q

HIV attaches to a specific protein receptor on helper T cells. A low percentage of people have a mutation of the CCR5 which codes for this protein receptor. This mutation results in a non functional protein receptor.
Explain how this mutation can result in the production of a non functional protein receptor. (4)

A
  • Change in DNA base/nucleotide (sequence);
  • Change in amino acid (sequence)/primary structure;
    Alters (position of) hydrogen/ionic/disulphide bonds;
  • Change in tertiary structure (of receptor);
20
Q

How many divisions do chromosomes go through in meiosis?

A

2

21
Q

How many daughter cells produced in meiosis?

A

4 genetically different daughter cells are produced

22
Q

What happens to the homologous chromosomes in the first meiotic division (simply) ?

A

Homologous chromosomes are separated

23
Q

What happens to the chromatids in the second meiotic division (simply)?

A

Chromatids are separated

24
Q

How does meiosis introduce variation?

A
  • Crossing over
  • Random assortment
25
Q

What is crossing over?

A
  • Occurs during prophase and metaphase of 1st division
    1. When chromosomes are being moved, homologous chromosomes attach to each other.
    2. As they are moved, it is possible that the chromatids will break at the attachment point (chiasmata).
    3. Enzymes reattach the fragments to the main chromosome but they may become attached to the other chromatid instead
26
Q

What is random assortment?

A
  • Occurs during metaphase in 1st division
    When the homologous chromosomes attach to the spindle fibres and they line up, it is random how they attach.
27
Q

What is non-disjunction?

A

When the chromosomes fail to separate correctly, resulting in gametes with one extra or one missing chromosome.

28
Q

Compare and contrast meiosis vs mitosis.

A
  • Meiosis has 2 divisions while mitosis has 1
  • Meiosis halves the number of chromosomes while mitosis doesn’t
  • Homologous chromosomes pair up in meiosis but not mitosis
  • Daughter cells are identical in mitosis but not in meiosis
  • 2 daughter cells produces in mitosis and 4 in meiosis
29
Q

Define life cycle.

A

The developmental stages that occur during an organisms lifetime.

30
Q

Describe the process of crossing over and explain how it increases genetic diversity. (4)

A
  1. During crossing over the chromatids get twisted around each other
  2. a portion from each homologous pair is exchanged.
  3. the alleles are exchanged
  4. increases genetic diversity because of new combinations
31
Q

Describe and explain the processes that occur during meiosis that increase genetic variation. (5)

A
  1. Crossing over leads to exchange of parts of alleles between homologous chromosomes
  2. both chromosomes create a new combination of alleles.
  3. Homologous chromosomes pair up.
  4. Independent segregation.
  5. Maternal and paternal chromosomes are random combination
32
Q

Meiosis results in cells that have the haploid number of chromosomes and show genetic variation. Explain how (6)

A

1) homologous chromosomes pair up
2) crossing over occurs (rare)
3) producing a new combination of alleles
4) chromosomes line up & separate at random
5) producing varying combinations of alleles
6) pairs of chromatid separated at meiosis 2
7)(some organisms are better adapted, survive & reproduce and passes on allele)

33
Q

What are homologous chromosomes?

A

Pairs of chromosomes with alleles for the same gene at the same loci and are the same size. However these alleles may be different, making each chromosome genetically different.

A-level Biology Year 1 (19 decks)

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