Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Biology Paper 1 A Level AQA > 3.4- Genetic information, variation and relationships between organisms > Flashcards

3.4- Genetic information, variation and relationships between organisms Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

What is a gene?

A

A small section of DNA that codes for the amino acid sequence of a polypeptide and a functional RNA (including ribosomal RNA and tRNAs).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Where are genes found?

A

On the locus of a particular DNA molecule.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is an allele?

A

A different version of the same gene.

Individuals have the same genes but there may be a slightly different base sequence/ version of the gene resulting in a different protein being formed.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe chromosomes.

A

Tightly coiled up DNA- located in nucleus in eukaryotic cells.

Humans have 23 pairs of chromosomes in the body cells.

Chromosomes are single threads of DNA when they are not undergoing cell division, after DNA replication in interphase: 2 copies of the chromosome are made- each ‘arm’ is called a chromatid. During mitosis, each chromatid is separated back into the chromosome.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are homologous chromosomes?

A

A pair of chromosomes that are exactly the same size, have the same genes but may contain different alleles.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How is DNA stored in a eukaryotic cell?

A

As chromosomes inside the nucleus which are linear in shape. To tightly coil the DNA so it can fit inside the nucleus as chromosomes, the DNA is tightly wound around proteins called histones- these prevent the DNA from getting tangled.

The length/amount of DNA of each cell in the body is the same.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is a nucleosome?

A

The complex of DNA wrapped around a histone.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is a triplet?

A

A sequence of 3 DNA bases that codes for a specific amino acid.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How is DNA stored in a prokaryotic cell?

A

The DNA molecules are much shorter and are circular.

Due to the DNA molecules being shorter, they are not wound around histones. The DNA is not associated with a protein.

DNA is free within the cytoplasm.

No introns.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the DNA like in the mitochondria and chloroplasts of eukaryotic cells?

A

The DNA is necessary to code for the enzymes involved in aerobic respiration in mitochondria and photosynthesis in chloroplasts.

The DNA is similar to the DNA in prokaryotic cells: it is shorter than eukaryotic DNA, it is circular and it is not associated with protein.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the start codon?

A

The first 3 bases/triplet at the start of a gene, copied onto mRNA.

Initiates translation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the stop codon?

A

The final 3 bases at the end of every gene that do not code for an amino acid.

There is no complementary anti-codon with a particular amino acid so the stop codons mark the end of a polypeptide chain and cause the ribosomes to detach, stopping translation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are the 3 features of the genetic code?

A

It is universal, degenerate and non-overlapping.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How do we know that 3 bases code for one amino acid?

A

20 amino acids that genetic code has to code for. 4 bases (CGTA), 3 are needed to make combinations to code for at least 20 amino acids.

Shown by 4^n

If 1 base coded for one amino acid there could only be 4 amino acids coded for. 4^1
If 2 bases coded for one amino acid there could only be 16 amino acids coded for. 4^2
If 3 bases coded for one amino acid there could be 64 amino acids coded for as 4^3=64. All 20 amino acids are covered.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

How is the genetic code degenerate?

A

64 base combinations is more than necessary to code for 20 amino acids, meaning that most amino acids are coded for by more than one triplet of bases.

Eg tyrosine coded for by ATA and ATG

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Why is the genetic code being degenerate a positive?

A

If there was a point mutation (one base was changed) then even though the triplet of bases would be different, it could still code for the same amino acid.

This is called a silent mutation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How is the genetic code universal?

A

The same triplet of bases codes for the same amino acid in all organisms, this allows genetic engineering to be possible.

Eg- inserting the human gene for insulin into bacteria. The bacteria can make the same protein insulin.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How is the genetic code non-overlapping?

A

Each base in a gene is only part of 1 triplet of bases that codes for 1 amino acid. Each codon/ triplet of bases is read as one unit.

This is an advantage as if there is a point mutation and a different amino acid is coded for, this would only affect 1 triplet base so 1 amino acid, reducing the effect on the polypeptide chain.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are introns?

A

Sections of DNA that do not code for amino acids and therefore polypeptide chains.

Known as ‘junk’ DNA.

Found only in eukaryotic DNA, they are spliced (removed) out of mRNA molecules.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What are exons?

A

The sections of DNA that code for amino acids. mRNA molecules and DNA in prokaryotes are only made of exons.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the genome?

A

The complete set of genes/DNA in a cell.

This should never change, may only change due to mutations.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is the proteome?

A

The full range of proteins that a cell is able
to produce.

Constantly changing depending on which proteins are currently needed- some genes are not always in use.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is messenger RNA?

A

A copy of 1 gene from DNA.

At the start of protein synthesis, the DNA can slightly unravel and a copy of this unravelled DNA is made in the mRNA. Created in nucleus and then leaves the nucleus to carry the copy of the bases of 1 gene to a ribosome.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Why can DNA not leave the nucleus?

A

DNA is too large to leave the nucleus and provide the genetic code. It is also at risk of being damaged by enzymes, destroying the genetic code.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Describe the structure of mRNA.

A

Single-stranded, every 3 bases code for a specific amino acid.

mRNA is much shorter than DNA as it is just a copy of the bases of one gene so it can leave the nucleus.

Short-lived as it is at the risk of enzymes hydrolysing the DNA/RNA polymers and breaking it down. Leaves the nucleus for an ideal amount of time.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Describe the function of mRNA.

A

Transfers the complementary DNA code out of the nucleus to the ribosome/ RER for protein synthesis to occur.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Describe the structure of tRNA.

A

Only found in the cytoplasm.

Single-stranded, but folds in on itself to create a cloverleaf shape held together by hydrogen bonds.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is transfer RNA?

A

To attach to one of the 20 amino acids and transfer it to the ribosome to create the polypeptide chain.

3 exposed bases at the top called the amino acid attachment site and the amino acid can be brought from here to the anti-codon.

Anti-codon describes the 3 bases on a tRNA molecule that are complementary to the 3 bases on a mRNA molecule. Complementary base pairing can occur between codon and anti-codon: amino acid brought to mRNA molecule.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is protein synthesis? + 2 stages?

A

The process where proteins are made, primarily on the ribosome. 2 stages:

1-transcription: where one gene on DNA is copied into mRNA

2-translation: where the mRNA joins with a ribosome and corresponding tRNA molecules bring the specific amino acid the codon codes for.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What happens during transcription?

A

A complementary mRNA copy of one gene on the DNA is made in the nucleus.

The mRNA is shorter than DNA, it is small enough to fit through nuclear pores in the nuclear envelope, so it can move into the cytoplasm and attach to the ribosomes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What are the steps of transcription?

A

1) The DNA double helix unwinds to expose the bases to act as a template, only 1 strand of DNA acts as a template.
2) This is catalysed by the enzyme DNA helicase, which breaks the hydrogen bonds between bases.
3) Free mRNA nucleotides in the nucleus align opposite their exposed complementary DNA bases- A+U, C+G. T+A
4) The enzyme RNA polymerase joins the adjacent RNA nucleotides together by condensation reactions forming phosphodiester bonds.
5) pre-mRNA is formed and this can then be spliced to remove introns

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What happens to the pre-mRNA in eukaryotic cells?

A

The pre-mRNA has to be modified to become mRNA so it can leave the nucleus and take part in translation.

The introns (sequences of bases in DNA that do not code for amino acids) are spliced out by a protein called a spliceosome- can break the phosphodiester bonds between the RNA nucleotides.

The finished mRNA is only made of exons.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What are the steps of translation?

A

1) Once the modified mRNA leaves the nucleus, it attaches to a ribosome at a start codon in the cytoplasm.
2) The tRNA molecule with the complementary anticodon to the start codon aligns opposite the mRNA, the ribosome holds them in place.
3) The ribosome moves along the mRNA molecule so the mRNA codon and a DIFFERENT complementary tRNA codon align.
Ribosomes bind no more than 2 tRNA molecules at the same time!
4) The 2 amino acids delivered by the 2 tRNA molecules are joined by a peptide bond, this bond requires ATP and is catalysed by an enzyme.
5) The next tRNA molecule with a complementary anticodon will join the codon, the previous tRNA will be attached and can be reused.
6) This occurs until the ribosome reaches the stop codon at the end of the mRNA molecule (the last 3 bases of mRNA that do not code for an amino acid)
7) The ribosome detaches and translation ends.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Describe how the production of mRNA in a eukaryotic cell is different from the production of mRNA in a prokaryotic cell.

A

mRNA is formed in the nucleus of eukaryotes, prokaryotes do not have a nucleus.

In prokaryotes, transcription results directly in the production of mRNA from DNA and the newly made mRNA does not need to be spliced as the genes in prokaryotes do not contain introns.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What is the DNA like in the mitochondria and chloroplasts of eukaryotic cells?

A

Like the DNA of prokaryotes: shorter, circular and not associated with protein.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

Describe the role of ATP in translation

A
  • Hydrolysis of ATP, to ADP + Pi, releases energy which is required for the process of translation.
  • For the bond between the amino acid and its corresponding tRNA molecule
  • Amino acid attaches at amino acid binding site
  • For peptide bond formation between amino acids
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

Describe the differences and similarities between the structure of a tRNA molecule and the structure of an mRNA molecule

A

Similarities- both are single polynucleotide strands.
Differences-mRNA is straight whereas tRNA is folded into a cloverleaf shape, mRNA is longer than tRNA, tRNA has an amino acid attachment site and mRNA contains no paired bases or hydrogen bonds whereas tRNA contains some.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Describe the role of ribosomes in translation

A

The ribosome attaches to mRNA and holds tRNA, allowing codon-anticodon complementary base pairing.
Allows peptide bonds to form between amino acids.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

Relate the base sequence of nucleic acids to the amino acid sequence of polypeptides.

A

tRNA anticodon is complementary to mRNA codon
Eg mRNA codon = ACG; tRNA anticodon = UGC

mRNA sequence of bases / codons are complementary to sequence of bases on DNA template strand
Eg mRNA base sequence = ACG UAG AAC; DNA base sequence = TGC ATC TTG

In RNA, uracil replaces thymine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

If the mRNA base sequence has a U, what will the nucleotide be for DNA? Eg- AUG mRNA to DNA

A

AUG= TAC

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

What is a gene mutation?

A

A change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide.

Mutations occur spontaneously and continuously- errors in DNA often occur during DNA replication.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

Name some causes of mutations?

A

Mutations that occur during the formation of gametes can be inherited.

Mutagenic agents such as: sunlight- increased exposure leads to thymine dimers in DNA, tobacco products, nitrites (processed meats), carcinogenic chemicals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

What is a gene point mutation?

A

Any change to 1 or more nucleotide bases, a change in the sequence of bases in DNA.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

What are the 3 ways nucleotides can alter the polypeptide chain?

A

Through insertion (addition), deletion and substitution.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

What is the insertion/addition of nucleotides?

A

When a nucleotide with a new base is inserted into the DNA sequence.

This changes the amino acid that would have been coded for by the original base triplet as it creates a different triplet of bases.

This could change the triplets further on in the DNA sequence- which is known as a frameshift mutation as it changes the amino acid sequence of the protein, so the polypeptide may not be able to function.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

What is the deletion of nucleotides?

A

When a nucleotide (and its base) is randomly deleted from the DNA sequence.

This changes the amino acid that would have been coded for, and it also affects the rest of the sequence by changing the remaining triplets. This is also known as a frameshift mutation.

This can change the amino acid sequence produced from the gene so the polypeptide may not be able to function.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

What is the substitution of nucleotides + 3 types?

A

When a nucleotide in the DNA sequence is randomly swapped for a different nucleotide that has a different base.

This will only change the amino acid for the triplet in which the mutation occurs, and will not have a negative effect on rest of sequence.

3 types- silent, missense and nonsense mutations.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

What are silent mutations?

A

When the mutation does not alter the amino acid sequence of the polypeptide as the genetic code is degenerate so more than one codon may code for the same amino acid.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

Why does a substitution mutation not always result in the change in the primary structure of a protein?

A

1) The substitution could have occurred in a non- coding region (intron)
2) The genetic code is degenerate so the same amino acid can still be coded for by the slightly different triplet of bases.

50
Q

What are nonsense mutations?

A

When the mutation creates a premature stop codon causing the polypeptide chain produced to be incomplete, affecting the final protein structure and function.

51
Q

What are missense mutations?

A

When the mutation alters a single amino acid in the polypeptide chain.

52
Q

What is non-disjunction?

A

When the chromosomes or chromatids do not split equally during anaphase of meiosis 1 or meiosis 2.

53
Q

What are chromosome mutations caused by non disjunction? + 2 types

A

Changes in the structure or number of whole chromosomes.

1) Changes in whole sets of chromosomes (polyploidy)
2) Changes in the number of individual chromosomes (aneuploidy)

54
Q

What are changes in whole sets of chromosomes? Polyploidy

A

When organisms have 3 or more sets of chromosomes, rather than 2. Known as polyploidy- occurs mostly in plants (eg hybridisation in wheat)

55
Q

How does polyploidy occur?

A

Non- disjunction in MEIOSIS 1

-All chromosomes are pulled to one side of the cell.
-Meiosis 2 occurs, chromatids separate, there are 2 gametes with no chromosomes whatsoever.
-2 other gametes have 2 copies of every chromosome in the gamete- diploid gametes not haploid gametes.
-If a diploid (2n) gamete fuses with a haploid (n) gamete, there are 3 sets of chromosomes.

Non-disjunction in MEIOSIS 2

-Chromosomes in meiosis 1 separate equally.
-Meiosis 2 produced 2 haploid gametes, but there was non-disjunction in the other cell.
-Spindle fibres did not form, chromatids are all pulled to one cell. Results in a diploid gamete and a gamete with no chromosomes.

56
Q

What are changes in the number of individual chromosomes? Aneuploidy

A

When individual homologous pairs of chromosomes fail to separate during meiosis. Known as non-disjunction, results in the gamete having either one more or one less chromosome.

Eg- Down’s syndrome: individuals have one additional copy of chromosome 21

57
Q

Explain why errors in DNA replication can be far more damaging than errors in transcription?

A

Unlike DNA, RNA does not permanently store genetic information in the cell.
Errors in transcription usually only affect specific cells whereas errors in DNA replication can be inherited as it is the ‘original’ so there can be a permanent effect on the entire body.

58
Q

Why is meiosis important?

A

It allows sexual reproduction of diploid organisms by forming gametes.

It enables genetic diversity/variation.

59
Q

What are the key differences between mitosis and meiosis?

A

Mitosis produces 2 daughter cells with the same number of chromosomes as the parent cell, meiosis produces 4 daughter cells with half the number of chromosomes as the parent cell.

Mitosis produces cells genetically identical to eachother and the parent cell, meiosis produces cells different from one another and the parent cell.

Mitosis produces 2 diploid daughter cells, meiosis produces 4 haploid daughter cells.

Mitosis is one nuclear division, meiosis is 2 nuclear divisions.

Mitosis occurs in stomatic (body) cells, meiosis happens in germ/sex cells.

60
Q

Describe the process of meiosis?

A

DNA replication occurs during late interphase.

During the 1st division, homologous chromosomes pair up and their chromatids wrap around each other. (Equivalent portions of these chromosomes are exchanged during crossing over.) The homologous chromosomes separate, one from each goes into 2 daughter cells.

During the 2nd division, sister chromatids move apart (centromere is divided), forming 4 haploid daughter cells.

61
Q

How does meiosis create genetic variation?

A

In meiosis 1: crossing over occurs during prophase 1 and independent segregation of homologous chromosomes during metaphase 1 which creates sets of chromosomes with new combinations of alleles.

62
Q

What is crossing over? 1ST DIVISION

A

Homologous chromosomes pair as bivalents and line up opposite each other at the equator in meiosis 1, parts of the chromatids can become twisted around each other.

Tension is put on the chromatid, causing pairs of the chromatid to break.

Broken parts of the chromatid recombine with the other non-sister chromatid- new combinations of genes on each chromosome.

63
Q

When does crossing over occur?

A

Prophase 1 of meiosis 1

64
Q

What is the chiasmata?

A

During meiosis 1, when homologous chromosomes are paired together, there are points along the chromosomes that make contact with the other pair. This point of contact is called the chiasmata.

65
Q

What is independent segregation? 1ST DIVISION

A

Homologous pairs line up opposite each other at the equator in meiosis 1

Which side of the equator the maternal and paternal chromosomes from the homologous pair lie is random

The pairs are separated, so one of each homologous pair ends up in daughter cell

Gamete will end up with 23 chromosomes after meiosis, but independent segregation means that each gamete has 1 of many different combinations of chromosomes..

66
Q

When does independent segregation occur?

A

Metaphase 1 in meiosis 1

67
Q

Difference between gene and chromosome mutations?

A

Gene mutations are due to random copying errors in DNA replication whereas chromosome mutations are due to non-disjunction in meiosis.

68
Q

How to calculate the possible combinations of chromosomes in the daughter cell produced? (INDEPENDENT SEGREGATION)

A

2^n

n=the number of homologous pairs

69
Q

How to identify meiosis in a life cycle?

A

Diploid (2n) parent cell divides to form haploid (n) cell.

Look in diagram for where cells go from diploid to haploid- only 1 copy of each chromosome.

70
Q

What creates the final increase in genetic variation?

A

The random fertilisation of gametes which produces new allele combinations.

71
Q

How to calculate possible combinations of chromosomes following sexual reproduction?

(AFTER FERTILISATION OF 2 GAMETES)

A

(2^n)^2

n= number of pairs of homologous chromosomes

72
Q

Describe + explain appearance of chromosomes before meiosis 1?

A

Chromosome consists of 2 sister chromatids held together by centromere as DNA replication has occurred.

73
Q

What is genetic diversity?

A

The number of different alleles of genes in a population, it is a factor enabling natural selection to occur: large number of different alleles in a population means a large variety of different characteristics and a high genetic diversity.

74
Q

‘What is a species?

A

A group of similar organisms that can breed together to produce fertile offspring.

75
Q

How can a mutation lead to a non functional enzyme?

A

A change in the DNA base sequence means there is a change in the amino acid sequence so there is a change in the hydrogen, ionic and disulphide bonds.

This changes the tertiary structure of the active site of the enzyme, so no more enzyme- substrate complexes can be formed.

76
Q

What is a population?

A

A group of individuals of the same species that occupy the same habitat at the same time.

77
Q

What is a habitat?

A

The place where an organism typically lives.

78
Q

How can genetic diversity be increased within a population?

A

1) Mutations in the DNA forming new alleles- can be beneficial or detrimental
2) Different alleles being introduced into a population when individuals from another population migrate into it and reproduce= gene flow.

79
Q

Describe what genetic bottlenecks are?

A

Events which cause a big reduction in the population, where a large number of organisms die before reproducing (eg-flood)

They reduce the number of alleles in the gene pool, reducing diversity. Only the random assortment of survivors reproduce, forming a larger population. New predominant allele will emerge and will pass on due to the small survivor’s population.

80
Q

Describe the founder effect?

A

This is what happens when only a few organisms from a population move away and start a new colony, there are a small number of diff alleles in initial gene pool.

Due to a shift in allele proportions, there will be a more predominant allele in the group which will be passed on and will become more common in the population.

Can occur as a result of migration leading to geographical separation.

81
Q

Describe the process of natural selection?

A

New alleles for a gene created by random mutations.

If new alleles increase the chance of the individual surviving in the environment, they are more likely to survive and reproduce.

This reproduction passes on the advantageous allele to next generation.

Over many generations, the new allele increases in frequency in the population.

82
Q

What is evolution?

A

Over time, natural selection leads to evolution- which is the gradual change in species over time, leading to the huge diversity of living organisms on Earth.

83
Q

What is meant by behavioural adaptations?

A

Ways an organism acts that increases its chance of survival.
Eg-possum playing dead if targeted by predator.

84
Q

What is meant by physiological adaptations?

A

Processes inside an organism’s body that increase its chance of survival.
Eg- brown bears hibernate to conserve energy.

85
Q

What is meant by anatomical adaptations?

A

Structural features of an organism’s body that increase its chance of survival.
Eg- whales have thick layer of blubber (fat) keeping them warm in cold sea.

86
Q

Describe selection?

A

The process by which organisms better adapted to their environment tend to survive + breed, whilst those less adapted tend not to.
Different environmental conditions favour different characteristics in the population.
Depending on characteristics favoured by particular selective pressure applied, selection will produce different results and can affect allele frequency differently.

87
Q

What are the 3 types of selection?

A

Directional, stabilising and disruptive.

88
Q

What is directional selection?

A

Where individuals with alleles for extreme characteristic are more likely to survive and reproduce.
Usually in response to an environmental change (selective pressure) or introduction of new advantageous allele in population.
Gradually changes the characteristics/allele frequencies of a population.

89
Q

What is an example of directional selection?

A

Antibiotic resistance in bacteria:

Some bacteria posses alleles which give them resistance to an antibiotic. If population is exposed to the antibiotic (directional selection), the bacteria with the alleles will survive and reproduce.

Antibiotic= selection pressure

90
Q

Draw 2 graphs to show difference in population before and after directional selection.

y axis= characteristic
x axis= frequency

A

mean of peak shifts to the right after selection, higher line.

91
Q

What is stabilising selection?

A

Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce.
When the environment is not changing, preserves the characteristics/allele frequencies of a population.

92
Q

What is an example of stabilising selection?

A

Human birth weight:
Small babies less likely to survive due to large SA:V ratio, hard to maintain body temp.
Large babies less likely to survive, struggle to fit through mum’s pelvis.
Natural selection keeps birth weights in the middle range.

93
Q

Draw a graph to show population before and after stabilising selection.

A

Line after selection will have very steep middle, line before selection will be regular increasing and decreasing curve.

94
Q

What is disruptive selection?

A

Where individuals with alleles for characteristics towards the middle of the range are less likely to survive and reproduce.
When an environment shows variation, results in polymorphism- continued existence of 2 or more distinct phenotypes in a population.

95
Q

What is an example of disruptive selection?

A

Bird beak size on Galapagos islands
There was a major drought where plants produced no or little seeds.
Birds with middle sized beaks were selected against as the seeds suited the birds with smallest beaks the most.

96
Q

Draw a graph to show population before and after disruptive selection

A

Before= normal curve up and down,
after= curve with dip in middle frequency of population.

97
Q

What is courtship behaviour?

A

Term given to the different behaviours that animals demonstrate to attract a mate.

This is essential for successful mating.

Most performed by males.

98
Q

What are examples of courtship rituals/behaviour?

A

Sequence of dance moves, sounds, display of colourful feathers.

Females observe and choose the male.

99
Q

Why is courtship behaviour important?

A

It increases the likelihood of successful mating as it enables individuals to recognise members of the same species and opposite sex.

Animals are more likely to mate when the female is releasing eggs as they will only display courtship behaviours when they are sexually mature and fertile: synchronises mating behaviour.

Leads to increased survival of offspring as the ritual forms a pair bond between the parents, so they may be more likely to stay together and raise the offspring.

Allows females to select a strong and healthy mate to reproduce with, ensuring more successful alleles are passed on.

100
Q

What is a binomial naming system? +rules

A

A two-name system where individuals are named after their genus and species: eg Homo sapiens (humans)

Genus (capital letter)- first name of a species which can be shared within multiple species.

species (lowercase)- specific name of one species: if this is not known we can write ‘sp’ eg Homo sp.

Universal- same everywhere and shows close relationship of species eg by having same genus.

101
Q

Why may different species look similar?

A

Live in a similar environment so have similar selection pressures, similar alleles will have selective advantage producing similar/the same proteins so similar characteristics.

102
Q

Describe phylogenetic classification.

A

It arranges species into groups according to their evolutionary origins and relationships- tells us who is related to who, and how closely related they are.

All organisms evolved from shared common ancestors shown on a phylogenic tree.

103
Q

How can the accuracy of phylogeny and classification be improved?

A

By advances in immunology and genome sequencing.

DNA base sequences of organisms for common genes can be compared as a measure for how closely related the organisms are. The more closely related the species, the higher the similarity between base sequences.

104
Q

Why can amino acids be used to show similarities between organisms?

A

Sequence of amino acids in the polypeptide chain of proteins can also be compared as this sequence is determined by DNA. The similarity between the amino acid sequence of the same protein in 2 species shows how closely related they are. Eg-cytochrome C is compared (in mitochondria) as most species have this protein.

105
Q

Describe artificial classification.

A

This is when organisms are grouped based on non-evolutionary, easily observable characteristics which may be of use- eg colour.

106
Q

What are the limitations of artificial classification/ using observable characteristics?

A

Many characteristics are polygenic- coded for by more than one gene so it is difficult to distinguish which genes are shared.

Environment also accounts for physical characteristics, not just genes.

107
Q

How can you see a hierarchy?

A

When there are smaller groups arranged within larger groups, there is also no overlap between groups.

108
Q

What is a taxon and its plural?

A

A taxon is a group within a hierarchy, more than one taxon= taxa.

109
Q

Example of a classification hierarchy?

A

domain, kingdom, phylum, class, order, family, genus and species

(dear king philip came over for good soup)

110
Q

How did the classification hierarchy change over time?

A

Went from a 5 kingdom classification (plants, animals, fungi, protists, bacteria) to a 3 domain classification (bacteria, eukarya, archaea.)

111
Q

Characteristics of bacteria, eukarya and archaea?

A

bacteria- no membrane bound organelles, unicellular, smaller r70s ribosomes, murein cell walls, no histones.

eukarya- have membrane bound organelles, DNA in nucleus, some have cell walls not from murein, larger 80s ribosomes.

archaea- their membranes contain fatty acid chains attached to glycerol by ester linkages, no murein in cell walls, more complex RNA polymerase.

112
Q

What are the 4 modern classification methods?

A

DNA sequence
mRNA sequence
amino acids sequence
immunological-comparing similarity in self-antibody shape

113
Q

What is biodiversity + 3 components?

A

the number and variety of living organisms in a particular area

1)species diversity: the number of different species and individuals of each species within a community.

2) genetic diversity- the variety of genes within the population of a species.

3) ecosystem diversity- the range of habitats.

114
Q

What is species richness?

A

The number of different species in an ecosystem at one time.

eg- 2 ecosystems may have the same species richness but different proportions.

115
Q

How to work out species diversity index?

A

N (N-1) /
Σ n(n-1)

N= total number of organisms of all species.
n= total number of organisms in each species.

the larger this value, the greater the species diversity.

116
Q

What is the species diversity index like in extreme environments?

A

There are much fewer surviving species with the necessary adaptations so the species diversity index is much lower.

The community’s stability is dominated by the climate rather than the species within it.

117
Q

Why is a high species diversity index favourable in most cases?

A

A higher species diversity index means there is a high stability in the ecosystem so there is a higher chance of at least one species having the necessary adaptations to survive with a change in environment.

118
Q

How does farming affect biodiversity?

A

Agriculture’s main goal is to maximise the yield of a selected set of animal and plant species, and by doing so it can ruin habitats/ biodiversity.

119
Q

What are some human actions which reduce biodiversity?

A
  • removal of habitats (eg hedgerows)
    -creating monocultures (eg when a meadow is replaced with 1 uniform crop)
    -filling in ponds
    -overgrazing of land
    -use of pesticides and fertilisers which can kill insects and lead to bioaccumulation.
120
Q

What are some conservation measures which try to balance out the impact of agriculture?

A

-creating/ maintaining ponds
-planting trees in areas of low SDI
-use organic fertilisers
-plant hedgerows to act as field boundaries rather than fences.

121
Q

What is the key principle behind immunological comparisons of proteins to investigate diversity?

A

Antibodies of one species will recognise/ respond to the antigens on the proteins of another species.

Often use albumin in blood (major protein in plasma)

122
Q

What are the best ways to investigate variation?

A

Taking samples as it would be too time-consuming/ impossible to measure data on every individual in a population.

Take a large sample to ensure it is representative of the entire population, can also use it to calculate a mean.

Use random sampling to avoid bias.

Biology Paper 1 A Level AQA (4 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions