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Biology > Topic 4: Genetic Info, variation + relationships > Flashcards

Topic 4: Genetic Info, variation + relationships Flashcards

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1
Q

Why is DNA a suitable molecule to carry genetic info?

A
  • DNA is a very stable molecule, so it rarely changes (/mutates)
  • DNA is a large molecule (polymer) so lots of info is carried
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2
Q

What reaction joins the 3 components of DNA together?

A

Condensation reactions

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3
Q

How do two adjacent nucleotides join together?

A

By a condensation reaction, forming a phosphodiester bond

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4
Q

What type of bond joins two opposite nucleotides together?

A

H bonds

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5
Q

How many different Amino Acids are there in lining organisms?

A

20

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6
Q

What ditermines the number + sequence of AAs in each polypeptide?

A

DNA base sequences, 3 DNA bases code for one AA

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7
Q

Why might a virus have a different % of adenine to thymine?

A

Viruses have single-stranded DNA

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8
Q

How is the structure of DNA related to its function?

A
  • The sugar phosphate backbone prevents physical + chemical damage
  • H bonds are individually weak, so DNA Helicase can break them
  • Large molecule, holds lots of info
  • Double-stranded, allows semi-conservative replication
  • Complementary base pairs allows accurate replication
  • Compact for storage
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9
Q

What is DNA like in Prokaryotes?

A

Shorter
Circular
No Histones (not associated with proteins)
ALL (non-viral) DNA IS DOUBLE-STRANDED

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10
Q

What is DNA in Eukaryotes like?

A

Protein-bound (histones)
Linear
V. Long

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11
Q

What are the components of chromosomes?

A

DNA (nucleotides) and associated proteins (Histones)

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12
Q

What is the DNA like in mitochondria and chloroplasts?

A

Same as prokaryotic DNA

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13
Q

What is the monomer of DNA?

A

Nucleotides

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14
Q

What is a gene?

A

A section of DNA with a sequence of nitrogen bases that carries a code

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15
Q

What do genes code for?

A
  1. Polypeptides

2. Functional RNA (tRNA and mRNA)

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16
Q

What is a locus?

A

The position of a gene on a chromosome

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17
Q

What is a chromatid?

A

2 Identical copies of the same gene found on a chromosome

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18
Q

What is a centromere?

A

Part of the chromosome that joins together two chromatids

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19
Q

What two processes, in order, are involved in creating polypeptides from DNA?

A

Transcription (DNA to mRNA)

Translation (mRNA to Protein)

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20
Q

What is the primary structure of protein?

A

The number and sequence of AAs

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21
Q

Why is the primary structure of proteins important?

A

It determines the location of Hydrogen, Ionic and Disulphide bonds which form between AAs.

The location of these bonds determines the secondary and tertiary structure of the protein

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22
Q

What are the names of the 4 nitrogen bases in DNA? Which ones pair up?

A

Adenine + Thymine,

Guanine + Cytosine

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23
Q

What is the formula for calculating the no. of amino acids that can be coded for when there are 4 nitrogen bases being read in groups of 3?

A

4 ^3 = 64

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24
Q

What would happen to the sequence of AAs in a polypeptide if the nitrogen base sequence was altered?

A

The AA base sequence in the polypeptide MAY change, it depends on the type of mutation because the genetic code is degenerate

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25
Q

Why is the genetic code said to be degenerate?

A

There are 64 possible triplet codes, but on 20 AAs, thus some AAs have multiple triplet codes.

eg TTT and TTC both code for Phe

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26
Q

What causes a stop codon?

A

Triplet codes that do not code for an AA, so no AA is added to the polypeptide chain - causing it to stop

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27
Q

What does degenerate mean?

A

One AA may be coded for by >1 triplet code

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28
Q

Why is the genetic code “non-overlapping”?

A

It is read every group of 3, not in between

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29
Q

Why is the genetic code universal?

A

The same DNA triplet codes for the same AA in (nearly) all organisms

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30
Q

What are mutations?

A

Changes to the nitrogen base sequence of DNA

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31
Q

What 4 factors cause DNA to mutate?

A
  • Spontaneous mutations upon replicating
  • Chemicals
  • Biological agents
  • Radiation
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32
Q

What is a frame-shift mutation?

A

A mutation which causes the code to be read differently after the point of mutation

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33
Q

What causes an insertion mutation?

A

Extra nitrogen bases being added

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34
Q

What causes a deletion mutation?

A

Nitrogen bases being removed

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35
Q

What causes a substitution mutation?

A

Nitrogen bases being replaced with different nitrogen bases

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36
Q

Which type of mutation may have no effect of the function of a protein? Why?

A

Substitution mutations

The genetic code is degenerate, so the same AA COULD still be coded for, so the corresponding protein will be the same

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37
Q

Why might a frame-shift (deletion/insertion) mutation have a greater effect if it is near the start of a gene?

A

The mutation may change the type of AA after the point of mutation (or cause a stop codon), so different bonds will form in different places, so the protein structure will change

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38
Q

Where can non-coding DNA be found?

A

In genes or between genes

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39
Q

What is the non-coding DNA found between genes called?

A

VNTRs (repeated units of the same base sequence)

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40
Q

What is the non-coding DNA found within genes called?

A

Introns (only in Eukaryotes)

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41
Q

What is the coding DNA found within genes called?

A

Exons (only in Eukaryotes)

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42
Q

Do porkaryotes have Introns and exons?

A

No

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43
Q

What is the genome of a cell?

A

The genetic material of an organism, consisting of DNA (but RNA in some viruses). Includes both genes and non-coding DNA

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44
Q

What is the proteome of a cell?

A

The entire set of proteins expressed by a genome, cell, tissue or organism at a certain time

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45
Q

In Transcription, what enzyme unzips DNA? How is this done?

A

DNA Helicase

Hydrogen bonds are broken

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46
Q

After DNA is unzipped by helicase in transcription, what happens next?

A

RNA nucleotides align themselves with one of the DNA strands (template strand), forming H bonds with the exposed bases

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47
Q

What RNA nucleotide is complementary to Adenine in DNA during transcription?

A

Uracil (instead of thymine)

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48
Q

Where does transcription take place?

A

Inside the nucleus of a cell

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49
Q

Where does translation take place?

A

In ribosomes in the cytoplasm or on the rough ER

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50
Q

How does mRNA leave the nucleus?

A

Via the nuclear pore

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51
Q

What enzyme joins adjacent RNA nucleotides together in transcription?

A

RNA polymerase

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52
Q

What happens to pre-mRNA before it leaves the nucleus?

A

It is spliced to remove introns

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53
Q

What does splicing do (transcription)?

A

Introns are removed (leaving exons) from pre-mRNA before it leaves the nucleus via a nuclear pore

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54
Q

Why does RNA polymerase only work in one direction?

A
  • It is an enzyme
  • Has a specific active site due to specific tertiary structure
  • The active site only binds to complementary-shaped RNA nucleotides (the substrate)
  • It would not fit going the opposite direction
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55
Q

How is mRNA adapted to its function?

A
  • Small, can move of the the nucleus into cytoplasm, via nuclear pore
  • Contains 4 nucleotides, carries the genetic code
  • Unstable, so hydrolysed quickly when no longer required, ensures that the cell doesn’t waste energy making proteins it doesn’t need
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56
Q

What is a transcription factor?

A

A protein/molecule that binds to specific DNA base sequences (promoter region), controlling the rate of transcription

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57
Q

How do Transcription Factors (TFs) act? (3 steps)

A
  1. TFs move from the cytoplasm to DNA
  2. Bind to promoter region on DNA
  3. Allows/ blocks the binding of RNA polymerase
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58
Q

What is a promoter region?

A

A region of DNA that RNA polymerase and TFs bind to to animate transcription

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59
Q

How does transcription in prokaryotes differ from eukaryotes?

A
  • mRNA directly produced in prokaryotes (no splicing as there are no introns)
  • Splicing is required in eukaryotes, so pre-mRNA is involved
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60
Q

What is an intron?

A

A region of DNA within a gene that does not code for amino acids

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61
Q

What is splicing?

A

The joining together of exons to produce mRNA ready for translation in the cytoplasm

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62
Q

Describe the structure of transfer RNA (tRNA)

A
  • Single stranded
  • Folded back on itself, leaving 3 unpaired N bases
  • The 3 unpaired bases form an anticodon, complementary to the codon on mRNA
  • H bonds form where the RNA polynucleotides fold

A clover leaf structure

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63
Q

What is the function of tRNA?

A

To carry specific amino acids in translation, complementary to the codon on mRNA

Forms a tRNA amino-acid complex

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64
Q

What reaction causes a peptide bond to form?

A

Condensation reaction to form a peptide bond

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65
Q

What are ribosomes made of?

A

2 sub-units: One large, one small

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66
Q

Do ribosomes occur singly?

A

No. Can be connected in groups called polyribosomes, connected by ribosomal RNA (rRNA)

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67
Q

How is tRNA adapted to its function?

A
  • Has amino acid binding site, allowing AAs to be carried in the cytoplasm
  • Anticodon is complementary to codons on mRNA, the pairing of codons with anticodons determines the order of AAs
  • tRNA is more stable than mRNA, so it can be used multiple times to pick up the same AA several times
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68
Q

What types of bond form in the secondary structure of proteins?

A

H bonds

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69
Q

What are the two types of secondary protein structure?

A

Alpha helix

Beta-pleated sheets

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70
Q

What 3 types of bond form in the tertiary structure of proteins, in order of strength?

A

H Bonds
Ionic bonds
Disulphide bonds

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71
Q

What is the structure proteins made up of >1 polypeptide called?

A

A Quaternary structure

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72
Q

How does the structure of tRNA differ form mRNA?

A
  • tRNA has some hydrogen bonds form at the anticodon region (no H bonds in mRNA)
  • tRNA has a cloverleaf structure, mRNA is linear, single stranded
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73
Q

Where does splicing take place?

A

In the nucleus

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74
Q

What happens during translation?

A

mRNA is read at ribosomes, allowing AAs to be joinde together to make a polypeptide

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75
Q

What are the 6 steps of translation?

A
  1. mRNA attaches to a ribosome and tRNA carries AAs to it
  2. The tRNA molecule carrying the AA joins to mRNA by complementary base pairing between the anticodon and condon respecively
  3. A second tRNA + corresponding AA joins in the same way
  4. The two AAs are joined by a peptide bond
  5. The first tRNA moves away, leaving the AA behind
  6. Another tRNA and comp AA join and the process continues until a stop codon is read and the polypeptide separates
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76
Q

What ‘tells’ the cell to start and stop translation?

A

The start and stop codons respectively

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77
Q

Why are individuals of the same species different from each other?

A

Variations in DNA (different alleles of the same genes)

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78
Q

Why is genetic variation important?

A

It may lead to adaptations the improve the chances of organisms’/species’ survival

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79
Q

What is genetic diversity?

A
  • Total number of different alleles in a population

- The more alleles in the population, the greater the genetic diversity

80
Q

What is a gene?

A

The base sequence of DNA that codes of amino acids (polypeptides) or a functional RNA (tRNA or rRNA)

81
Q

What is an allele?

A

An alternative form of the same gene

82
Q

Why can mutations sometimes be good?

A

Some mutations may be beneficial to an organism, coding for a protein which give an individual an advantage in certain conditions

83
Q

What are the two GENERAL types of mutation

A
  1. Gene mutation

2. Chromosome mutation

84
Q

What is a gene mutation?

A

A change to one or more nucleotide bases or sequence of bases within a gene

85
Q

What is a chromosome mutation?

A

A change in the structure or number of chromosomes

86
Q

What is something that increases the rate of mutations?

A

A mutagenic agent

87
Q

How might a substitution mutation of one AA cause a faulty protein to be formed?

A
  • Substituted AA may not form the same H/ionic/disulphide bonds
  • The tertiary structure of the protein changes
  • The function of the protein may also change if the functional site changes shape too
88
Q

Give and example of a disorder caused by a substitution mutation.

(for essays…)

A

Sickle Cell Anaemia

Causes Haemoglobin to stick together so red blood cells block capillaries

89
Q

Why do substitution mutations sometimes not cause any change to the amino acid in a polypeptide?

A
  • The genetic code is degenerate
  • The substitution may code for the same AA
  • So the protein will be the same shape (reference bonds)
90
Q

What is non-disjunction?

A

When individual homologous chromosomes fail to separate during meiosis - the resultant gamete has one more or one less chromosome than normal

91
Q

What 5 things need to be covered when explaining the effect of mutations on proteins/enzymes

A
  1. Nature of the mutation (frame-shift) causes the base sequence of the gene to change
  2. Causes different AAs to be coded for in protein synthesis
  3. H/ionic/ disulpide bonds form in different places
  4. Protein folds differently
  5. Tertiary structure changes so active/functional site no longer complementary to substrate
  6. Reference the effect on the metabolic pathway etc
92
Q

What does MITOSIS result in?

A
  • 2 genetically identical daughter cells

- Same number of chromosomes (DIploid)

93
Q

What does MEIOSIS result in?

A
  • 4 genetically different daughter cells
  • Each cell has half the no. of chromosomes (HAploid)
  • Produces gametes
94
Q

What is the purpose of mitosis?

A

For growth and repair of cells and tissues

95
Q

What is the purpose of meiosis?

A
  • Produces gametes

- Introduces genetic variation in offspring

96
Q

How does meiosis cause genetic variation?

A
  • Crossing over of alleles
  • Independent segregation of homologous chromosomes
  • Random fertilisation of gametes
97
Q

What is meant by ‘diploid’?

A

Chromosomes in homologous pairs

98
Q

What are homologous chromosomes?

A
  • Two chromosomes carrying the same genes (One from each parent)
  • The chromosomes carry a different allele of each gene
99
Q

What is an allele?

A

An alternative form of a gene

100
Q

What are the two general stages (1 and 2) of meiosis?

A
  1. Separation of homologous chromosomes

2. Separation of chromatids

101
Q

What happens in prophase 1 of MEIOSIS?

A
  • Chromosomes coil up and become visible
  • Spindle fibres form
  • Homologous chromosomes pair up
  • Chromatids wrap around each other (crossing over and recombination)
  • Genetic material is exchanged at chiasmata
102
Q

What happens in metaphase 1 of MEIOSIS?

A
  • Homologous pairs of chromosomes line up on the cell equator
103
Q

What happens in anaphase 1 of MEIOSIS?

A

One of each homologous pair (still 2 sister chromatids) moves to each pole

104
Q

What is the random alignment of homologous chromosomes in metaphase 1 of MEIOSIS called?

A

Independent assortment

105
Q

What happens in telophase 1 of MEIOSIS?

A

2 daughter cells form, each with one of each pair of homologous chromosomes

106
Q

What happens in meiosis 2?

A

Sister chromatids separate (like in mitosis) to make 4 haploid daughter cells

107
Q

What two processes cause variation in meiosis?

A

Crossing over

Independent segregation

108
Q

What is independent segregation (meiosis)?

A

The random alignment of pairs of homologous chromosomes along the equator of the cell

109
Q

What is a population?

A

A group of individuals of the same species living in the same place.

Can breed to produce fertile offspring

110
Q

What is a gene pool?

A

All the genes and their various alleles that exist in a population at a specific time

111
Q

What is alllele frequency?

A

The number of times the allele of interest is observed in all the alleles of a gene in a population

112
Q

What causes high genetic diversity?

A

A great variety of alleles in a population

113
Q

Why is high genetic diversity important?

A

There are a large variety of alleles, and this characteristics (phenotypes) in a population so more individuals will survive if the environment changes

(by natural selection)

114
Q

What 5 points are required in an answer on natural selection?

A
  1. Random mutation = New allele which is advantageous in certain environments (introduces variation)
  2. Individuals with new allele are better adapted to the environment, surviving more competition
  3. Individuals with allele survive and reproduce to pass on allele to next generation (REPRODUCTIVE SUCCESS)
  4. Next gen also have allele and thus survive + reproduce
  5. Allele frequency increases over many generations as breeding success also increases
115
Q

What is selection?

A

The process whereby organisms that are better adapted to the environment survive and breed. Those without the adaption will not

116
Q

What does phenotype mean?

A
  • The characteristic that comes form a combination of alleles
  • Observable physical and chemical characteristics of an organism
117
Q

What is directional selection?

A

Selection for a particular characteristic may favour individuals that vary in one direction away from the mean of the original population

The normal distribution curve will move from the mean as the environment changes and individuals without advantageous allele will not survive and thus reproduce

118
Q

What is an example of directional selection?

A

Antibiotic resistance in bacteria

119
Q

TRUE OR FALSE

Bacteria mutate because of antibiotics

A

FALSE

  • Bacteria may possess a mutant allele prior to exposure to antibiotics and thus survive
  • Mutations are random and the effectiveness of a mutation depends on the environmental circumstances
120
Q

What sort of selection occurs in stable environmental conditions?

A

Stabilising selection

121
Q

What occurs in stabilising selection?

A

Individuals with phenotypes closest to the mean are more likely to survive and pass on their alleles to the next gen

Those with phenotypes at the extremes are less likely to do so

122
Q

What is an example of stabilising selection? How does it work?

A

Human birth weights

Babies with low birth mass loose heat + susceptible to disease. Babies of larger mass are more difficult to deliver. Babies of medium mass will survive

123
Q

In what way does stabilising selection affect the genetic diversity of a population?

A

Less diverse because phenotypes at extremes are eliminated

124
Q

What effect does stabilising selection have on the SD and mean of populations?

A

SD becomes smaller, mean unchanged

125
Q

What effect does directional selection have on the SD and mean of populations?

A

SD unchanged, mean translated to favourable phenotype

126
Q

What are the similarities between Mitosis and Meiosis?

A
  • Both involve DNA replication in S phase of interphase

- Both use PMAT (Prophase, Metaphase, Anaphase and Telophase) although the processes do differ

127
Q

What are the differences between Mitosis and Meiosis?

A
  • Meiosis involves 2 divisions (2x PMAT)
  • Meiosis produces 4 haploid gametes (variation)
  • Mitosis creates 2 genetically identical cells
128
Q

What is a species?

A
  • Similar to other members of the same species (physically and biochemically)
  • Occupy the same ecological niche
  • Can breed to producing living, fertile offspring
129
Q

What is taxonomy?

A

The science of classification

130
Q

Why is taxonomy important?

A
  • There are millions of species on earth
  • Many have similar features
  • Allows humans to organise groups by features
131
Q

What does a phylogenetic system do?

A

Organises species by evolutionary relationships

132
Q

What is a binomial (in terms of taxonomy)?

A

Two name

Homo sapiens

(First word capitalised; both in italics or underlined)

133
Q

What is the advantage of using a binomial system?

A
  • Clarity (avoids confusion with common names)
  • Stability (Latin name meanings don’t change)
  • Unique for each species
  • Universally used worldwide
134
Q

What is the order of taxa?

A 
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
135
Q

What is a mnemonic for remembering the order of taxa?

A 
D
King 
Prawn
Curry 
Or 
Fairly
Greasy 
Sausage
136
Q

What contains more organisms family or class?

A

Class because it is higher in the hierarchy than family

137
Q

Why is courtship behaviour important for mating?

A
  • Allows animals to recognise members of the same species
  • Identifies a mate that is capable of breeding
  • To form a pair bond to successfully raise young
  • Syncronises mating
138
Q

How can scientists determine evolutionary relationships nowadays?

A
  • Genome sequencing on electrophoresis gel

- Immunology

139
Q

How DID scientists determine evolutionary relationships in the past?

A

By observation alone because of lack of technology

140
Q

Why do changes to gene sequences allow the relationships between organisms to be made?

A

The more recent the common ancestor is, the less time has passed between the gene of the two species, so less mutations have (occurred in less time)

141
Q

When establishing differences between species why must the same gene be compared?

A
  • Similar base sequence (some bases in common)

- Complementary bases will bind together by H bonds

142
Q

Besides DNA sequencing, what other techniques are used to determine the relationship between species?

A
  1. mRNA sequencing (only expressed genes as introns are removed during splicing in transcription)
  2. Protein sequencing
143
Q

Is it better to use a specific gene to some organisms when comparing genetic relationships or a gene present in all species?

A

A gene present in all species

eg Cytochrome is a protein involved in respiration so it is present in all eukaryotes. This is more appropriate than haemoglobin because only present in some organisms. Ensures comparisons can be made

144
Q

How can immunology be used to establish evolutionary relationships between organisms?

A
  • Antigens have a similar shape
  • Thus tertiary protein structure will be similar
  • Primary structure + DNA sequencing will be similar
  • Antigens can be tested on antibodies to test the complementary shape (causes antibody antigen complexes to form)
145
Q

What is a population?

A
  • All the organisms of one species
  • In a given area
  • At a given time
146
Q

What is a community?

A
  • All the populations of different species
  • In a given area
  • At a given time
147
Q

What is species richness?

A

The variety of species present in a community

148
Q

What is the index of diversity?

A

The variety of species present as well as abundance of each species in a community

149
Q

Why is the index of diversity better than species richness?

A
  • Species richness gives no indication of the size of each species’ pop
  • If a species population is low then it is easier for one individual to die/ not reproduce
150
Q

What 4 farming practices directly affect biodiversity?

A
  1. Removal of hedgerows and woodland
  2. Creating mono-cultures
  3. Filling ponds and draining marshland
  4. Overgrazing land
151
Q

What 3 farming practices indirectly affect biodiversity?

A
  1. Use of pesticides and inorganic fertilisers
  2. Escape of effluent
  3. Lack of intercropping and crop rotation
152
Q

What is a gene pool?

A

All the genes in a population

153
Q

Why is it important to maintain genetic diversity?

A

Some individuals are more likely to survive within a population if the environment changes

154
Q

What two reasons make it ethically wrong to reduce biodiversity?

A
  1. It causes reduction/ loss of populations

2. Less organisms present for future generations

155
Q

Name 3 commecial limitations of reduced biodiversity

A
  1. Less medicine
  2. Less tourism in biodiversity hotspots
  3. Agricultural issues (eg. less pollination)
156
Q

What is selective breeding?

A

Artificial selection

Individuals with desired characteristics are selected for breeding

157
Q

How does selective breeding affect biodiversity?

A

Reduces genetic diversity over generations because undesirable phenotypes are not bred

158
Q

What is the founder effect?

A
  1. A new population of only a few alleles is established on an island
  2. The population breeds and one allele becomes more frequent through inbreeding
  3. Occurs by chance
159
Q

What is a genetic bottleneck?

A
  • Occurs when a disaster reduces a once large population to a small one very quickly
  • Only the alleles in the survivors are found in the surviving population
160
Q

What for methods are adopted to compare diversity between species?

A
  1. Frequency of observable characteristics
  2. Base sequence of DNA
  3. Base sequence of mRNA
  4. Amino acid sequence of proteins encoded by DNA and mRNA
161
Q

What must scientists do in order to perform quantitative investigations of variation within a species?

A
  • Collect data from random samples

- Calculate the mean and SD

162
Q

How can scientists collect samples randomly? (4 steps)

A
  1. Set up a grid
  2. Random no. generator to select coordinates
  3. Use a large sample size so less influence of chance/anomalies, more representative of the actual population
  4. Statistical analysis of the data
163
Q

Why should a large sample size be used when sampling?

A

Reduces the influence of chance and anomalies so that the sample is more representative of the actual population

164
Q

Why is it important that scientists collect their samples randomly?

A
  • Avoids bias

- Prevents the desired outcome being prioritised in the sample

165
Q

Why do scientists carry out statistical tests?

A

To see of their experimental results are due to the independent variable or due to chance alone

166
Q

What does a null hypothesis usually say?

A

That there is no difference between the data being compared.

Assumes that the differences are due to chance

167
Q

Why is it better to use standard deviation instead of range?

A

Outliers have more of an effect on range

SD looks at variation around a mean

168
Q

When would you use a chi-squared test?

A

When looking at the difference between the data you observe and the data you were expecting

169
Q

When would you use a t-test?

A

When looking at the difference between two means

170
Q

When would you use a Spearman’s rank correlation coefficient test?

A

When looking for a correlation between an independent variable and a dependent variable

171
Q

What would a null hypothesis for a Chi-squared test be?

A

“There is no difference between the observed (specify) and expected (specify) values.”

(chi-squared looks at the difference between the data you observe and the data you were expecting)

172
Q

What would a null hypothesis for a t-test be?

A

“There is no difference between mean 1 (specify) and mean 2 (specify).”

(t-test looks at the difference between two means)

173
Q

What would a null hypothesis for a Spearman’s rank correlation coefficient test be?

A

“There is no correlation between the independent variable (specify) and the dependent variable (specify).”

(Spearman’s rank looks at a correlation between an independent variable and a dependent variable.)

174
Q

What happens if the value from a chi-squared or t-test calculation is greater than/equal to the critical value?

A

Reject NH (there is a significant difference)

175
Q

What are gametes?

A

Haploid cells that combine during fertilisation to form a zygote which subsequently divides + develops into a new organism by mitosis (for growth)

176
Q

Why is meiosis used for sexual reproduction?

A

It produces haploid daughter cells which then fuse during fertilisation to make a diploid cell with the correct number of chromosomes

177
Q

What does crossing over do to introduce variation?

A

Each of the 4 daughter cells contains chromatids with different alleles

178
Q

How many divisions does mitosis involve?

A

1

179
Q

How many divisions does meiosis involve?

A

2

180
Q

Why doesn’t mitosis introduce variation?

A

There is no crossing over or independent segregation because there is no pairing or separation of homologous chromosomes

181
Q

What (sometimes) causes chromosome mutations?

A

Errors in mitosis because the homologous chromosomes are not accurately moved to the cell poles (issues with spindle fibres for example)

Called non-disjunction of chromosomes

182
Q

How does genetic diversity increase within populations?

A
  • Mutations in DNA forming new forms of alleles

- Different alleles being introduced into a population due to migration from other populations (gene flow)

183
Q

What is the founder effect an example of?

A

A genetic bottleneck

184
Q

What are the three types of adaptation?

A
  1. Behavioural adaptations
  2. Physiological adaptations
  3. Anatomical adaptations
185
Q

What is an example of stabilising selection?

A

Human birth weights

186
Q

What does the first branch point on a phylogenetic tree represent?

A

A common ancestor of all the family members

187
Q

Why is courtship behaviour species specific?

A

Ensures that only members of the same species respond to the courtship behaviour so that living, fertile offspring are produced

Prevents interbreeding

188
Q

How does courtship help to reduce interbreeding?

A
  • Species specific
  • Members of only the same species recognise each other
  • Members of other species do not mate, so no infertile offspring are produced
189
Q

What three techniques are used to clarify evolutionary relationships?

A
  1. Genome sequencing
  2. Comparing amino acid sequences
  3. Immunological comparisons
190
Q

Why is using amino acid sequences to determine evolutionary relationships between organisms less reliable than genome sequencing?

A

mRNA is spliced in transcription, so whilst the same proteins may be produced, the genetic code may be different because introns are no accounted for

191
Q

What, in basic term, is genetic diversity?

A

The number of different alleles in a population

192
Q

Why are samples of populations used to study variation?

A
  • A census is time consuming and it will be difficult to catch all the individuals in the group
  • Samples can be used as accurate models of the whole population
193
Q

How can samples be less biased?

A

Using a random sample so that no sample frame is favoured

194
Q

How can a random sample be taken to study the plant species in a field?

A

Divide the field into a grid and use a random number generator to select coordinates

195
Q

What is a habitat?

A

The place where an organism lives

Biology (10 decks)

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