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Biology A-Level OCR > Genetics and Evolution (Module 6) > Flashcards

Genetics and Evolution (Module 6) Flashcards

1
Q

What is a mutation?

A

A random or spontaneous change to the sequence of bases in DNA

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2
Q

What are the different types of mutation?

A

Substitution, deletion and insertion

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3
Q

What are substitution mutations?

A

When one or more nucleotides are substituted, which causes a change in codon, therefore amino acid sequence and primary structure of a protein

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4
Q

What is degenerate code?

A

When, in substitution mutations, when the codon changes it still codes for the same amino acid; so does not change the primary shape of the protein

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5
Q

What are insertion mutations?

A

When one or more nucleotides are inserted into a DNA base sequence

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6
Q

What are deletion mutations?

A

When one or more nucleotides are deleted from a DNA base sequence

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7
Q

What do deletion and insertion mutations cause?

A

Frameshifts, which has much worse effects as some genes are unfinished as codons are always 3 bases. Lots of bases also change amino acid formation

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8
Q

What are the three outcomes of mutations?

A

No outcome, damaging outcome, beneficial outcome

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9
Q

Name some mutagens (chemical, physical or biological agent that increases likelihood of mutation)?

A

Ionizing radiation, deaminating agents, alkylating agents, base analogs, viruses

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10
Q

What are the different types of chromosomal mutations?

A

Deletion, duplication, translocation, inversion

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11
Q

Why are chromosomal mutations worse than other mutations?

A

Because there are more genes condensed than are effected

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12
Q

What is the difference in gene expression between eukaryotes and prokaryotes?

A

The stimuli that trigger transcriptional enzymes to be activated

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13
Q

What are the different ways gene expression can be controlled?

A

Transcriptional, post-transcriptional, translational, post-translational

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14
Q

What are genes regulated by?

A

Protein based hormones

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15
Q

What are some transcriptional control mechanisms?

A

Chromatin remodeling, Lac Operon, Histone modification

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16
Q

What is chromatin remodeling in transcriptional control?

A

When DNA is either tightly wound into heterochromatin (so it cannot be accessed by RNA polymerase to be transcribed from) or loosely wound into euchromatin (so DNA can be accessed by RNA polymerase for transcription)

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17
Q

What is histone modification in transcriptional control?

A

DNA (negatively charged) is wrapped around positively charger histones. Acetyl or phosphate groups can be added to DNA to make the histones less positive so the DNA is wound less tight (for access for transcription), or methyl groups can be added to make the histones more positive, so DNA is bound tighter (less access for transcription)

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18
Q

What is Lac Operon?

A

A form of gene expression where a repressor protein binds to a promoter region, which prevents the binding of RNA polymerase so transcription cannot ensue. If glucose/lactose is present, it binds to the repressor- causing it to change shape and so cannot bind to the promoter region; RNA polymerase can bind for transcription.

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19
Q

What is the role of cyclic AMP? (cAMP)

A

Catalysing the lac operon mechanism to speed it up, when glucose is present, forms ATP instead to inhibits lac operon.

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20
Q

What are introns and exons?

A

Introns are non-coding DNA and exons are coding DNA

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21
Q

What happens during pre-translational control?

A

Introns are removed from pre-mRNA (splicing) and modified nucleotides are provides at both ends (5’ and 3’) to form ‘caps’ and ‘tails’.

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22
Q

Why does mRNA need ‘caps’ and ‘tails’?

A

To help stabilise the molecule and prevent degradation in the cytoplasm

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23
Q

What is RNA editing in pre-translational control?

A

When mRNA molecules have addition, deletion or substitution (point) mutations to increase the range of proteins that can be made from a single RNA molecule.

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24
Q

What mechanisms control protein synthesis? (transcriptional control)

A

Degradation of mRNA, binding of inhibitory proteins to mRNA, activation of initiation factors (aid binding of mRNA to ribosomes)

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25
Q

What are some mechanisms for post-translational control?

A

Addition of non-protein groups (carbohydrates, phosphate, lipids), modifying amino acids/formation of bonds, folding/shortening proteins, modification of cAMP

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26
Q

What are body plans?

A

A small group of genes that regulate anatomical development

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27
Q

What are hox genes?

A

A subset of homeobox genes that regulate ONLY animal anatomical development

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28
Q

What are homeobox genes?

A

A sequence of 180 bases that are involved in regulating anatomical development in animals, plants and fungi

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29
Q

What are homeotic genes?

A

An ancient family of genes involved in controlling anatomical development

30
Q

What are homeodomain proteins?

A

Proteins that contain a homeodomain sequence, they act as transcription factors to activate or repress genes that regulate mitosis, apoptosis and the cell cycle

31
Q

Give an example of a homeobox mutation

A

Pax6 gene, that when mutated causes blindness due to an underdeveloped retina- occurs in humans, mice and fruit flies.

32
Q

How many hox genes do humans have?

A

39

33
Q

In body plans, what is a common feature of animals?

A

They are segmented and have symmetry

34
Q

What types of symmetry occur in animals?

A

Radial symmetry, bilateral symmetry, asymmetry (sea sponges)

35
Q

What is apoptosis?

A

Programmed cell death

36
Q

What is necrosis?

A

Uncontrolled cell death

37
Q

How does apoptosis occur?

A

Cytoplasm and nucleus gets denser, blebbing occurs, cell chrinkage, then the nucleus ‘fragments’ and blebs break off into apoptotic bodies break off and then are engulfed by phagocytes

38
Q

What is the difference between discontinuous and continuous variation?

A

Continuous: genetics that CAN be affected by environment and genetics, and is presented as a line graph. Discontinuous: genetics that CANNOT be affected by environment, only genetics- presented as a bar chart.

39
Q

What factors can affect gene expression?

A

Internal: stress, hormones or psychological distress External: temperature, light intensity, drugs

40
Q

How is genetic variation achieved?

A

Combination of gametes from parents via sexual reproduction

41
Q

What is a phenotype?

A

The observable characteristics of an organism

42
Q

What is a genotype?

A

Genetic make-up of an organism with respect to genes

43
Q

What is the difference between homozygous and heterozygous genes?

A

Homozygous is when there are two of the same genes (recessive or dominant), and heterozygous is when there is one of each

44
Q

Give some examples of discontinuous variation

A

Blood group, round/winkled pea shape, albinism

45
Q

Give some examples of continuous variation

A

Leaf surface area, animal mass, skin colour

46
Q

What is codominance?

A

When both genes for one characteristic are both dominant, and present themselves equally

47
Q

What are autosomes?

A

Every other type of chromosomes other than sex chromosomes

48
Q

What is sex linkage?

A

Characteristics determined by genes of sex chromosomes (X and Y)

49
Q

List some examples of sex-linked disorders

A

Colorblindness, hemophilia, intersex

50
Q

Why are females less likely to have sex-linked disorders?

A

Because they need the mutated gene on both X chromosomes, whereas males only have one X chromosome so are more likely to be a sufferer

51
Q

What is haemophilia?

A

A sex-linked disorder that mutates the gene that forms blood clots

52
Q

What is autosomal linkage?

A

Genes that are linked on the same chromosome and are inherited as a unit, are not separated by meiosis until chiasmata

53
Q

What is the equation for recombinant frequency?

A

number of recombinant offspring/total offspring

54
Q

What is recombinant frequency?

A

Measuring the amount of crossing over that happens in meiosis in a dihybrid cross

55
Q

What is a dihybrid cross?

A

A Mendel genetic cross that determines the offspring of two linked autosomal characteristics

56
Q

Determine the meaning behind the recombinant frequency equation

A

> 50%, no linkage. <50%, some linkage.

57
Q

What is epistasis?

A

Interaction of genes at different loci, for example gene regulation (lac operon).

58
Q

What type of variation is often linked to epistasis?

A

Continuous variation

59
Q

How does epistasis work?

A

When considering genes a, b and c, gene a makes enzyme A, which catalyses a reaction at precursor a to make precursor b… and so on.

60
Q

What is the difference between dominant and recessive epistasis?

A

If two recessive genes at a loci led to an effect on gene expression, then that is recessive epistasis. If one or both of the genes at the loci were dominant and caused an effect, then that is dominant epistasis (which can lead to masking)

61
Q

What is masking in epistasis?

A

In dominant epistasis, the dominant allele will ‘mask’ the recessive allele in a heterozygous pair.

62
Q

What is a hypostatic gene?

A

A gene that is affected by another gene

63
Q

What is an epistatic gene?

A

A gene that affects another gene

64
Q

What is the formula for allele frequency?

A

p + q = 1 p(dominant) q(recessive)

65
Q

What is the Hardy-Weinberg principal?

A

A principal which states that ‘in a stable population with no disturbing factors, the allele frequencies will remain he same so evolution will not occur.’ This is not accurate as there commonly is no ‘stable’ population.

66
Q

What are some factors that affect evolution?

A

Mutation, sexual selection, gene flow, genetic drift, natural selection, the founder effect (genetic drift with natural disaster)

67
Q

What are density dependent and independent factors?

A

Limiting factors that can decrease the population, for example:
Dependent (on population size): competition, predation, disease and parasitism
Independent (of population size): climate change, natural disasters, seasonal change, human activities

68
Q

What is stabilising selection?

A

A bell shaped graph that has the normal as the positive selection, and extremes as negative selection. Therefore the negative selective genes are reduced via natural selection… changing the allele frequency

69
Q

What is directional selection?

A

When the most extreme phenotype variations occur more frequently due to a change in environment, such as the peppered moths (only one phenotype)

70
Q

What is disruptive selection?

A

When both of the extreme phenotypes in a population are more frequent, which is the opposite to stabilsing selection.

Biology A-Level OCR (26 decks)

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