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AQA A-Level Biology 1-4 > 4.3 Mutation and Meiosis > Flashcards

4.3 Mutation and Meiosis Flashcards

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1
Q

When do mutations usually occur?

A

Replication

Cell division

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2
Q

What are mutations?

A

Any change to the DNA of an organism; either the quantity of DNA or the base sequence

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3
Q

What are the two type of mutation?

A

Gene

Chromosome

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4
Q

What are gene mutations?

A

A change in the base sequence of the DNA of an organism

Happens during DNA replication

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5
Q

What are chromosome mutations?

A

A change in the number or structure of whole chromosomes

Happens during cell division

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6
Q

Are mutations in somatic cells passed on? Why?

A

No

Inherited cells are only from gametes in meiosis

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7
Q

If you have a change in the base sequence of DNA what also changes?

A 
Base sequence of mRNA
Amino acid sequence 
Hydrogen bonds
Tertiary structure of protein
Protein function
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8
Q

What are the 3 main type of gene mutations?

A

Substitution
Addition
Deletion

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9
Q

What is a substitution mutation?

A

One base in the DNA is switched for a different base

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10
Q

What are addition and deletion mutations?

A

Addition - one base is inserted into the DNA

Deletion - one base is removed from the DNA

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11
Q

What are the consequences of a substitution mutation?

A

Non-sense mutation: results in a stop codon

Mis-sense mutation: causes a different amino acid to be coded for

Silent mutation: the substituted base code for the same amino acid = no effect

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12
Q

What are the consequences of addition and deletion mutations?

A

Frame shift
Causes all subsequent codons to be altered
Can be devastating if at the start of a gene

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13
Q

What causes mutations?

A 
Ionising radiation
Carcinogens
Genetic/Inherited
Age
Random
Microorganisms
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14
Q

What happens in meiosis?

A

DNA is replicated from the parent cell
The homologous pairs are separated
Then the chromatids are separated to form 4 genetically varied daughter cells each containing half the number of chromosomes of the parent cell

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15
Q

Why is it important the chromosome number is halved in meiosis?

A

DNA is halved so the diploid number is restored and we don’t double chromosomes every generation

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16
Q

How does meiosis lead to variation?

A

Crossing over
Independent segregation of homologous chromosomes
Independent segregation of homologous chromatids

17
Q

How does sexual reproduction lead to variation?

A

Crossing over
Independent segregation of homologous chromosomes
Independent segregation of homologous chromatids

Random fusion of gametes

18
Q

What is crossing over?

A

In prophase 1 the homologous chromosomes can tangle and some exchange of alleles between chromatids can take place

This can result in chiasmata’s - a point where the chromosomes have crossed over

19
Q

What is independent segregation of chromosomes?

A

How the chromosomes line up in metaphase 1 as orientation is random

20
Q

What is independent segregation of chromatids?

A

How the chromatids are oriented which determines which pole they are moved to before separation into cells

21
Q

How many divisions are there in meiosis? Resulting in?

A

2 divisions

4 genetically variable daughter cells that are haploid

22
Q

Describe phase 1 of meiosis?

A

Genetic material is replicated, cell grows and organelles synthesised
Homologous chromosomes pair up
The homologous chromosomes line up along the equator (spindle fibres help)
The spindle fibres contract to separate the chromosomes to each pole which halves the chromosome number

23
Q

Describe phase 2 of meiosis?

A

The chromosomes line up along the equator not in pairs
The chromatids separate when the spindle fibres contract
The membrane reforms and 4 haploid daughter cells are produced

24
Q

How can you tell the difference between prophase 1 and 2?

A

In prophase 1 the chromosomes will be in pairs crossed over

25
Q

How can you tell the difference between mataphase 1 and 2?

A

Metaphase 1 will have homologous chromosomes lined up side by side on the equator

Metaphase 2 will have chromosomes lined up alone

26
Q

On a life cycle diagram where will fertilisation take place?

A

Just before the genetic material is doubled

27
Q

On a life cycle diagram where will meiosis take place?

A

Just before the genetic information has split

28
Q

What does asexual reproduction lead to?

A

Clones

Genetically identical

29
Q

How can chromosomal mutations occur?

A

The failure of chromatids to separate in anaphase 2 of meiosis therefore you could end up with 1 too many or too few chromosomes

30
Q

What is a chromosomal abnormality/disease?

A

Down’s syndrome

Extra 21st chromosome

31
Q

What affects the risk of down’s syndrome? Why?

A

The age of the mother

The eggs are older therefore something going wrong in meiosis phase 2 is more likely

AQA A-Level Biology 1-4 (20 decks)

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