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A Level Bio > Chapter 9 - Gene Diversity And Adaptation > Flashcards

Chapter 9 - Gene Diversity And Adaptation Flashcards

1
Q

What is a mutation

A

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

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2
Q

What is a gene mutation

A

A change in the sequence of bases that results in the formation of a new allele

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3
Q

3 types of gene mutations

A
  • base deletion (known as point mutation as it occurs at a single point)
  • base substitution (also known as point mutation as it occurs at a single point)
  • base insertion
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4
Q

When does gene mutation occur

A
  • spontaneously during dna replication
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5
Q

What is a chromosome mutation

A

Any changes in the structure or number of whole chromosomes

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6
Q

When do chromosome mutations occur

A

During the process of meiosis

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7
Q

Two forms of chromosome mutations and how the occur

A
  • changes in whole sets of chromosomes - occur when organisms have 3 or more sets of chromosomes rather than 2, is called polyploidy
  • changes in the number of individual chromosomes - occurs during non disjunction which is where individual homologous pairs of chromosomes fail to separate during meiosis resulting in a gamete having one more or fewer chromosomes
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8
Q

What happens during dna substitution

A
  • a nucleotide in a DNA molecule is replaced by another base
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9
Q

Why might base substitution NOT have an effect

A

Due to degenerate coding as most amino acids have more than one codon that codes for the same amino acid so there will be no change in the polypeptide produced and so the mutation will have no effect

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10
Q

Why might base substitution HAVE an effect

A

The polypeptide produced will differ in a single amino acid which may form different bonds in different locations that would effect the tertiary structure of the final protein, causing the protein to be a different shape and therefore not function properly

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11
Q

What happens during base deletion

A

A nucleotide is lost from the normal base sequence

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12
Q

Why can base deletion have a major effect

A

One deleted nucleotide causes all triplets in a sequence to be read differently as each has been shifted to the left by one base, which is called frame shift mutation the left so this will change the amino acid sequence of the encoded polypeptide, therefore changing the primary structure of the protein causing bonds to form in different places in the tertiary structure which will cause the proteins structure and function to change

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13
Q

3 types of base substitution and what they do

A

Nonsense mutation - changes triplet codon to stop codon
Misense mutation - changes triplet codon to code for another amino acid
Silent mutation: when a different triplet codon codes for the same amino acid due to degenerate coding (or any change that does not have an effect)

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14
Q

What is produced in meiosis

A
  • Daughter cells that are genetically DIFFERENT from each other
  • 4 haploid daughter cells from a single diploid parent cell
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15
Q

What are haploid cells and diploid cells

A

Cells that contain only one set of chromosomes - haploid
Cells that contains two sets of chromosomes - diploid

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16
Q

Two mechanisms that introduce variation of cells in meiosis and when they occur

A
  • Independent segregation of homologous chromosomes
  • Crossing over between homologous chromosomes
  • both happen during the first division of meiosis
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17
Q

What are homologous chromosomes

A

Pair of chromosomes with the same gene sequence, loci, centromere location and chromosomal length but different alleles (one chromosome comes from mum the other from dad)

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18
Q

What happens in independent segregation

A

1) in meiosis 1 the homologous pairs of chromosomes line up opposite each other at the equator of the cell
2) it is random which side of the equator the paternal and the maternal chromosomes from each homologous pair lie
3) these pairs are separated so one of each homologous pair ends up in the daughter cell
4) this creates a large number of possible combinations of chromosomes in the daughter cells produced

19
Q

How can you calculate the number of possible combinations of chromosomes in the daughter cell produced in independent segregation

A

2^n
n = number of homologous pairs/ pairs of chromosomes

20
Q

What happens during crossing over

A

1) in meiosis 1 the homologous pairs line up opposite each other at the equator and parts of the chromatids from each homologous pair can become twisted around each other
2) this puts tension on the chromatids causing the pair of chromatids to break
3) the broken parts of the chromatids recombine with chromatids of the other homologous chromosome
4) equivalent proportions are exchanged
5) this results in new combinations of alleles

21
Q

Comparison of meiosis to mitosis

A

Meiosis
- two nuclear divisions
- produces haploid cells
- introduces genetic variation
Mitosis
- one nuclear division
- produces diploid cells
- creates genetically identical cells

22
Q

How to identify meiosis in a cell cycle

A
  • it’s the point of the cell cycle where the cells are turning from a diploid cell (2n) to a haploid cell (n)
23
Q

How to calculate the possible combinations of GAMETES

A

(2n)^2

24
Q

Stages of meiosis - meiosis 1

A

1) before meiosis starts the cell would have gone through interphase where the cell copies its chromosomes and the organelles
2) then the cell enters meiosis 1 where prophase 1 occurs, and the chromosomes condense and become visible and the homologous chromosomes link together to form chiasmata through the process of crossing over which will exchange alleles between the homologous chromosomes and at the same time the nuclear membrane breaks down and centrioles move to opposite poles of the cell and spindle fibres start to assemble into the spindle apparatus
3) in metaphase 1 the pair of homologous chromosomes line up at the equator of the cell and are attached to the spindle fibres
4) during anaphase 1 the spindle fibres shorten and the homologous chromosomes move to opposite poles and the chiasmata between homologous chromosomes break
5) in telophase 1 the nuclear membranes reform and the chromosomes uncoil back to their chromatin state and at this point the cell undergoes cytokinesis dividing into two haploid cells
6) then the cells enter meiosis 2

25
Q

Stages of meiosis - meiosis 2

A

1) in prophase 2 the chromosomes condense and become visible again and the nuclear membrane breaks down and spindle fibres begin to develop
2) in metaphase 2 the chromosomes are lined up on the equator of the cell and are attached to spindle fibres
3) in anaphase 2 the centromere of each chromosome divides and the spindle fibres shorten, the chromatids are then pulled to opposite poles of the cell
4) in telophase 2 the chromatids reach the poles of the cell and are referred to as chromosomes, the nuclear membranes reform and the chromosomes uncoil back to their chromatid state and each cell undergoes cytokinesis to produce two haploid cells each

26
Q

What is selection

A

The process by which organisms that are better adapted to the environment survive and breed

27
Q

What is genetic diversity

A

The number of different alleles in a population

28
Q

What is a population

A

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

29
Q

When does natural selection occur

A

If there is a genetic diversity within a population

30
Q

What is natural selection

A

The process that leads to evolution in populations

31
Q

What is evolution

A

The change in allele frequency over many generations in a population

32
Q

Different types of adaptions names

A

Anatomical - structural features
Physiological - chemical reactions in the body
Behavioural - how organisms behave to increase its chance of survival

33
Q

Process of natural selection

A

1) within any generation there will be a gene pool containing a variety of different alleles
2) random mutations of alleles within the gene pool results in new alleles to be formed
3) in certain environments the new allele may give the organism an advantage over the other individuals in the population, so will be better adapted and more likely to survive in competitions with others
4) these organisms will be more likely to obtain resources and grow more rapidly and live longer so will have a higher chance of breeding successfully and producing more offspring , passing on their genes to the next generation
5)so the new individuals will have the advantageous alleles so are more likely to breed and pass on their genes
6) over time the frequency of the new advantageous allele will increase whilst the non advantageous allele will decrease

34
Q

Types of natural selection

A
  • directional selection
  • stabilising selection
35
Q

What is directional selection

A

When a single phenotype to a particular environment is favoured causing the allele frequency to shift away from the mean

36
Q

When does directional selection occur

A

When there is a change in the environment

37
Q

What is stabilising selection

A

When the individuals with the phenotype closest to the mean are favoured when the environmental conditions remain stable

38
Q

What happens in stabilising selection

A

Individuals with extreme traits are less likely to survive so the individuals with phenotype closer to the mean will pass on their genes causing their to be a higher frequency of individuals with alleles closer to the mean

39
Q

Environmental factors that exert selection pressure (determine which individuals will do best at surviving or reproducing)

A
  • availability of resources
  • abiotic factors (non living)
  • biotic factors
40
Q

What is the founder effect

A

The reduction in genetic variation that results when a subset of a large population is used to establish a new colony, which causes the new population to be different from the original population

41
Q

What is genetic drift

A

The change in frequency of an existing genotype in the population due to random chance causing particular genes to disappearance as individuals die or not reproduce

42
Q

What is genetic bottleneck effect

A

Is an extreme example of genetic drift when the size of a population is severely reduced

43
Q

Advantages of greater genetic diversity

A

The greater genetic diversity the greater the chance an organism will survive an environmental change as the more alleles the greater probability that some individuals have alleles better suited for the environment

44
Q

Apart from mutation explain how one other genetic variation within a species is increased

A
  • Random fusion of gametes
  • produces new alleles combinations

A Level Bio (15 decks)

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