3.4 Genetic information, variation and relationships between organisms

Question 1

What is an allele?

Answer 1

Different version of a gene

Question 2

Explain how DNA replicates.

Answer 2

Semi-conservative replication:
- DNA helicase breaks hydrogen bonds
- Produces two template strands
- DNA nucleotides line up by complimentary base pairs
- DNA polymerase joins nucleotides together by phosphodiester bonds, forming sugar phosphate backbone

Question 3

What are 2 advantages of DNA molecules having two DNA strands?

Answer 3

1. Protects bases
2. Makes semi-conservative replication possible

Question 4

Compare and contrast the DNA in eukaryotic cells with the DNA in prokaryotic cells.

Answer 4

Compare
- Both have identical nucleotide structure
- Phosphodiester bond

Contrast
- Eukaryotic DNA is longer
- Histones
- Introns/exons
- Ciruclar vs linear

Question 5

Describe how the DNA in a chloroplast is different to the DNA in the nucleus of a eukaryotic cell.

Answer 5

• Chloroplast DNA is circular, nucleus is linear
• Chloroplast DNA not associated with histones, nucleus is
• Chloroplast DNA has no introns, nucleus does

Question 6

Describe the nature of the genetic code (3)

Answer 6

• Degenerate
• Non-overlapping
• Universal

Question 7

Define ‘non-coding base sequence’ and describe where the non-coding sections of the DNA are positioned in the genome.

Answer 7

• DNA that does not code for a polypeptide
• Positioned between genes

Question 8

What is a homologous pair of chromosomes?

Answer 8

Parent chromosomes that carry the same genes (same loci) and code for the same characteristics

Question 9

What is the proteome?

Answer 9

All of the proteins produced by the genome

Question 10

What is an autosome?

Answer 10

A non-sex chromosome

Question 11

Give 2 ways in which the structure of tRNA differs from mRNA.

Answer 11

• mRNA is a single helix, tRNA has a clover leaf shape
• mRNA contains codons, tRNA contains anticodons

Question 12

Describe how a gene is transcribed in the nucleus of a cell.

Answer 12

• DNA helicase breaks hydrogen bonds
• One strand acts as a template, RNA nucleotides pair up with complimentary bases on the template strand
• RNA polymerase forms the sugar phosphate backbone (phosphodiester bonds) to proude a pre-mRNA molecule
• Molecule is spliced to remove introns and produce the mRNA

Question 13

Describe the process of translation.

Answer 13

• mRNA associates with a ribosome
• tRNA has complimentary anticodon to each codon of this mRNA molecule
• Each tRNA molecule also has a specific amino acid
• As each codon is read by the ribosome the amino acid from the complimentary tRNA is added in the correct sequence to form a polypeptide chain by condensation reactions (peptide bonds)

Question 14

What point mutations cause a frame shift?

Answer 14

Addition and deletion

Question 15

What are the 3 impacts that base substitution can have on a protein?

Answer 15

1. Silent- codes for same amino acid (degenerate nature of genome)
2. Nonsense- codes for a stop codon
3. Missense- codes for new amino acid

Question 16

How can a base substitution lead to the formation of a non-functioning enzyme?

Answer 16

• Base substitution causes amino acid sequence chnages as new amino acid coded for
• This changes the ionic/hydrogen/disulphide bonds and so tertiary structure of enzyme changes
• Active site changes shape, no longer complimentary to substrate so fewer E-S complexes form

Question 17

Give 2 factors that could increase the frequency at which a mutation in DNA occurs.

Answer 17

1. Exposure to ionising radiation (x-rays)
2. Exposure to carcinogens (tobacco tar)

Question 18

Name the processes that occur during meiosis that increase genetic variation.

Answer 18

1. Crossing-over
2. Independent assortment

Question 19

Describe the process of crossing-over and explain how it increases genetic diversity.

Answer 19

• Homologous pair of chromosomes form a tetrad during prophase I
• 2 non-sister chromatids form a chiasma at the point they cross and exchange equal lengths of alleles
• This produces new combinations of alleles

Question 20

Describe the process of independent assortment and explain how it increase genetic diversity.

Answer 20

• It is the random orientation of homologous chromosome pairs along the spindle fibres during metaphase I
• Maternal and paternal chromosomes reshuffled

Question 21

What are the stages of meiosis?

Answer 21

Meiosis I (interphase + pmat + cytokinesis)
Meiosis II (pmat + cytokinesis)

Question 22

How many daughter cells does meiosis produce?
Are they haploid or diploid?

Answer 22

4 haploid daughter cells

Question 23

What is the formula to calculate the number of combinations of chromosomes after the random fertilisation of two gametes?

Answer 23

2^n

Question 24

What causes mutations in chromosome number during meiosis?

Answer 24

Non-disjunction

Question 25

What happens if abnormal gametes (wrong number of chromosomes) are fertizlied?

Answer 25

- Aneuploidy/polyploidy, - Genetic disorders like Down's syndrome can occur

Question 26

What is the gene pool?

Answer 26

The total number of different alleles (total genetic diversity) within a population

Question 27

How is the gene pool of a population increased?

Answer 27

- Mutations - Migration into area - Gene flow

Question 28

How is the gene pool of a population decreased?

Answer 28

- Genetic bottlenecking - Founder effect - Genetic drift

Question 29

What is genetic bottleneck?

Answer 29

- Population size decreases significantly due to an event - Smaller gene pool - Remaining population breed, passing on the few alleles they have amongst themselves, alleles become more common in offspring

Question 30

What is the founder effect?

Answer 30

- Small number of individuals seperate from original population - Taking with them their alleles: smaller gene pool and possibly an increased proportion of individuals with a certain allele

Question 31

What is gene flow and genetic drift?

Answer 31

Gene flow = introduction of genes from one population of a species to another via migration Genetic drift = change in frequency of genes in population due to random chance

Question 32

What are the 3 types of selection and the environment quality for each?

Answer 32

1. Disruptive- selection pressure 2. Directional- change in environment 3. Stabilising- stable environment

Question 33

Name some common selection pressures.

Answer 33

- Prey/food - Mates - Environment - Disease - Predation

Question 34

What are the 3 types of adaptions?

Answer 34

1. Anatomical- structural features 2. Behavioural- organism action 3. Physiological- biological processes

Question 35

What 2 types of variation are there?

Answer 35

1. Intraspecific variation- a species 2. Interspecific variation- different species

Question 36

What is a species?

Answer 36

Organisms which can mate to produce fertile offspring

Question 37

Why is courtship behaviour important?

Answer 37

Ensures there is successful mating within a species

Question 38

Give 3 ways curtship behaviour can increase the probability of successful mating.

Answer 38

- Allows individuals to recognise and attract member of same species - Able to identify a fertile/sexually mature mate - Able to identify a mate of the opposite sex

Question 39

What is classification and what 5 methods can you use to help classify organisms?

Answer 39

- How species are organised into groups 1. Morphology 2. Amino acid sequence comparison 3. Immunological comparison 4. DNA hybridisation 5. DNA base sequence comparison

Question 40

What is the difference between artificial and phylogenetic classification?

Answer 40

- Artificial looks at common features and function, phylogenetic looks at evolutionary origon (common ancestors) - Artificial based off analagous characteristics but phylogenetic based off homologous characteristics

Question 41

What is a hierarchy?

Answer 41

Groups within groups which are non-overlapping

Question 42

How do you classify species?

Answer 42

Kingom Phylum Class Order Family Genus Species

Question 43

What are the 3 domains?

Answer 43

1. Bacteria 2. Archae 3. Eukarya

Question 44

What are the 4 types of eukarya? How do they differ?

Answer 44

1. Protoctista 2. Animal 3. Plant 4. Fungi cell wall (is it present, what is it made out of), how they feed (saprotroph, autotroph, heterotroph)

Question 45

How can differences in the primary structure of proteins provide evidence of phylogenetic relationships between species?

Answer 45

- Mutations change base sequence - Change in amino acid sequence - Mutations increase over time - More mutations between more distantly related species - Distantly related species have earlier common ancestor

Question 46

What is biodiversity and what is it made up of?

Answer 46

Biodiversity = variety of organisms in a community - Species diversity = species abundance/richness - Ecosystem diversity = range of different habitats - Genetic diversity = variety of genes within community

Question 47

Why is it important to have a high level of biodiversity?

Answer 47

- Helps with survival of specie when there are selection pressures or a change in environement. - Protects them from loss of food sources and habitats

Question 48

What can cause a decline in biodiversity?

Answer 48

- Over-farming/fishing - Climate change - Pollution - Deforestation

Question 49

How can farming lower biodiversity?

Answer 49

- Monoculture, limited species richness and variety - Use of herbicides/pesticides - Removal of hedges and trees - Over-grazing by farm animals - Lack of biomass, other species have to compete with small remainder of food, water, space

Question 50

What conservation techniques are being used in farming?

Answer 50

- Crop-rotation - Organic farming - Replanting trees

Question 51

How would you take a random sample in an area?

Answer 51

- Draw a grid of area and randomly select coordinates using a random number generator - Take sample at area where this coordinate lies, repeat for many different coordinates (at least 20)