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AS-Level Biology (AQA) > 4.2 (9) - Genetic Diversity > Flashcards

4.2 (9) - Genetic Diversity Flashcards

Mutations Meiosis and genetic variation Genetic diversity and adaptations Types of selection

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1
Q

What is a gene mutation?

A

Any change to one or more nucleotide bases, or a change in the sequence of bases, in DNA

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2
Q

What is base substitution?

A

Where a nucleotide in a DNA molecule is replaced by another nucleotide that has a different base

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3
Q

How does base substitution affect the final polypeptide?

A

The final polypeptide will differ only in 1 amino (codon with 3 bases) - the significance of this depends upon the exact role of the original amino acid

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4
Q

What is base deletion?

A

Where a nucleotide is lost from the normal DNA seuqence

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5
Q

How does base deletion affect the final polypeptide?

A

The DNA’s sequence of bases is read differently because each has been shifted to the left by 1 base, causing the final polypeptide to function incorrectly

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6
Q

What is a chromosome mutation?

A

A change in the structure/number of whole chromosomes

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7
Q

What are 2 types of chromosome mutations?

A

Changes in:

  • whole sets of chromosomes
  • number of individual chromosomes
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8
Q

When does a change in whole sets of chromosomes occur?

A

Occurs when organisms have 3 or more sets of chromosomes (polyploidy), rather than 2

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9
Q

When does a change in the number of individual chromosomes occur?

A

Occurs when individual chromosomes fail to separate during meiosis, which usually results in a gamete having ±1 chromosome

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10
Q

What is meiosis?

A

The special form of cell division used to produce gametes (sex cells)

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11
Q

What is the purpose of meiosis?

A
  • To form haploid cells with half the chromosome number

- To re-arrange the chromosomes with a new combination of alleles

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12
Q

Describe the process of meiosis 1 in 6 stages

A

1) Interphase
- start with 2 single chromatids
- DNA is copied

2) Prophase 1
- the doubled chromosomes pair up
- recombination (crossing over) occurs

3) Metaphase 1
- Chromosomes line up at the equator

4) Anaphase 1
- Chromosomes are pulled apart by meiotic spindle

5) Telophase 1
- Cell pinches in the middle

6) Cytokinesis
- Cells separate, due to a ring of protein filament around the cell that tightens - results in 2 daughter cells

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13
Q

Describe the process of meiosis 2 in 5 stages

A

1) Prophase 2
- 2 daughter cells

2) Metaphase 2
- Chromosomes line up at the equator of each cell

3) Anaphase 2
- Sister chromatids are pulled apart by meiotic spindle

4) Telophase 2
- Both cells pinch in the middle

5) Cytokinesis
- Cells separate, due to a ring of protein filament around the cells that tightens - results in 4 granddaughter cells

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14
Q

Describe the process of meiosis in 11 stages

A

1) Interphase
- start with 2 single chromatids
- DNA is copied

2) Prophase 1
- the doubled chromosomes pair up
- recombination (crossing over) occurs

3) Metaphase 1
- Chromosomes line up at the equator

4) Anaphase 1
- Chromosomes are pulled apart by meiotic spindle

5) Telophase 1
- Cell pinches in the middle

6) Cytokinesis
- Cells separate, due to a ring of protein filament around the cell that tightens - 2 daughter cells

7) Prophase 2
- 2 daughter cells

8) Metaphase 2
- Chromosomes line up at the equator of each cell

9) Anaphase 2
- Sister chromatids are pulled apart by meiotic spindle

10) Telophase 2
- Both cells pinch in the middle

11) Cytokinesis
- Cells separate, due to a ring of protein filament around the cells that tightens - results in 4 granddaughter cells

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15
Q

What are the 2 sources of genetic variation in sexual reproduction?

A
  • Genetic recombination by crossing over

- Independent segregation of homologous chromosomes

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16
Q

What is a chiasma?

A

The point at which chromatids are in contact during crossing over

17
Q

What is the point at which chromatids are in contact during crossing over called?

A

Chiasma

18
Q

What is crossing over?

A
  • In prophase 1, the chromatids become twisted around each other
  • During the twisting, tensions are created and portions of the chromatids break off - they may re-combine with their homologous partner (recombination)
  • There are always equal amounts crossed over, so chromosomes stay the same length
19
Q

What is the purpose of crossing over?

A

Maternal and paternal alleles can be mixed (provides new combinations of alleles)

20
Q

What is independent segregation?

A

In meiosis 1, chromosomes can line up along the cell’s equator in any order, resulting in different possible combinations

21
Q

What is non-disjunction?

A

When pairs of homologous chromosomes fail to separate during meiosis

22
Q

How do you work out the number of combinations of chromosomes?

A

2∧n, where n = the number of pairs of homologous chromosomes

23
Q

What does genetic diversity mean?

A

The number of different alleles in a population

24
Q

What is a population?

A

A group of individuals of the same species that live in the same place and can interbreed

25
Q

What is allele frequency?

A

The number of times a specific allele occurs

26
Q

What are 2 types of selection?

A
  • Directional selection

- Stabilising selection

27
Q

What is directional selection?

A

Directional selection is where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce

28
Q

What is stabilising selection?

A

Stabilising selection is where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce

29
Q

What are three adaptations based on natural selection?

A
  • Anatomical
  • Physiological
  • Behavioural
30
Q

What is an anatomic adaptation? Give an example

A

An adaptation to do with physical features (eg. thicker fur or short ears)

31
Q

What is an physiological adaptation? Give an example

A

An adaptation to do with the inner workings of the body (eg. oxidising fat rather than carbohydrates to produce water)

32
Q

What is an behavioural adaptation? Give an example

A

An adaptation to do with an organism’s behaviour (eg. migration)

AS-Level Biology (AQA) (11 decks)

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