Genetic information, variation and relationships between organisms

Question 1

Define genome

Answer 1

Complete set of genes present in a cell

Question 2

Define gene

Answer 2

A sequence of DNA bases that codes for a polypeptide or functional RNA

Question 3

1 mark

Define proteome

Answer 3

Full range of proteins a cell can produce

Question 4

2 marks

Explain a mutation, which involved the addition of one nucleotide within a sequence

Answer 4

1. Frameshift / all triplets moved
2. So affects more than one amino acid

Question 5

2 marks

Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule.

Answer 5

1. Condensation reaction–> loss of water
2. Between phosphate and deoxyribose
3. Catalysed by DNA polymerase

Question 6

6 marks

Describe DNA transcription

Answer 6

1. Section of DNA unwinds using DNA helicase
2. Hydrogen bonds break
3. Single strand used as template
4. Free RNA nucleotide attach to exposed bases
5. Free RNA nucleotides join using complementary base pairings (A-U & G-C)
6. RNA polymerase joins RNA nucleotides in a condensation reaction, forming phosphodiester bonds
7. Until stop codon is reached
8. Pre- mRNA is spliced to remove introns

Question 7

2 marks

Describe how the production of messenger RNA (mRNA) in a eukaryote cell is
different from the production of mRNA in a prokaryote cell.

Answer 7

1. Pre-mRNA only produced in eukaryote cell
2. Splicing only occurs in eukaryote cell
3. Introns removed in eukaryote cell/ introns not present in prokaryote cell

Question 8

2 marks

Describe the role of ATP in the process of translation in protein synthesis.

Answer 8

1. Releases energy
2. So peptide bonds form between amino acids
   OR
   So amino acid joins to tRNA

Question 9

Similarities and differences between RNA and DNA

Answer 9

Similarities
1. Polymers of nucleotides;
2. (Nucleotide has) pentose, (nitrogen-containing organic) base and a phosphate (group);
3. Cytosine, guanine and adenine (as bases);
4. Have phosphodiester bonds;

Differences
5. Deoxyribose v ribose;
6. Thymine v uracil;
7. Long v short;
8. Double helix/stranded v single stranded;

Question 10

4 marks

Explain how mutation can result in production of a non-functional protein receptor

Answer 10

1. Change in DNA base- mutation changes triplet/ causes frameshift
2. Change in amino accid sequence
3. Alter position of hydrogen/ionic/disulfide bonds
4. Change in tertiary strucure

Question 11

5 marks

Starting with mRNA in the cytoplasm, describe how translation leads to the box production of a polypeptide.
Do not include descriptions of transcription and splicing in your answer.

Answer 11

1. mRNA molecule attaches to ribosome
2. Ribosome moves to the start codon
3. tRNA carries specific amino acid
4. Anticodon on tRNA complementary to codon on mRNA
5. Ribosome can fit two tRNAs
6. Amino acids join by peptide bonds in a condensation reaction to form a polypeptide using ATP

Question 12

Define homologous pair of chromosomes

Answer 12

2 chromosomes that carry the same genes

Question 13

6 marks

Describe what happens to chromsomes in meoisis

Answer 13

1. Chromosomes condense
2. Chromosomes associate in homologous pairs
3. Crossing over
4. Join to spindle fibres
5. at equator of cell via centromere
6. Homologous pairs move to opposite poles
7. Pairs of chromatids seperated in 2nd division

Question 14

4 marks

Describe how the process of meiosis results in haploid cells.
Do not include descriptions of how genetic variation is produced in meiosis.

Answer 14

1. DNA replication
2. Two divisions
3. Separation of homologous chromosomes in first division
4. Separation of sister chromatids in second division
5. Produces 4 haploid cells

Question 15

Explain how chromosome number is halved

Answer 15

1. Homologous chromosomes (pair);
2. One of each (pair) goes to each (daughter) cell / to opposite poles;

Question 16

4 marks

Explain crossing over

Answer 16

1. Chromatids can become twisted around each other
2. This puts tension on chromatids
3. Causing pairs of the chromatid to break
4. Broken parts of chromatid recombine with another chromatid
5. =New combination of alleles

Question 17

3 marks

Explain how crossing over can contribute to genetic variation

Answer 17

1. Sections of chromatids exchanged
2. Sections have different alleles
3. New combination of alleles

Question 18

2 marks

Explain why meosis is important in sexual reproduction, apart from producing gametes that are genetically different

Answer 18

1. Produces haploid cells
2. Restoring diploid number
3. Introduces genetic variation

Question 19

5 marks

Meiosis results in genetic variation in the gametes which leads to variation in the offspring formed by sexual reproduction.
Describe how meiosis causes this variation and explain the advantage of variation to the species.

Answer 19

1. Crossing over
2. Independent segregation
3. Random fertilisation
4. Different adaptations
5. Some survive
6. To reproduce
7. Pass on allele

Question 20

The offspring produced from farmed trout are sterile. Suggest and explain why.

Answer 20

1. Too many copies of chromosomes
2. Homologous chromosomes do not pair
   OR
   Homologous chromosomes do not separate
   evenly
3. So no meiosis

Question 21

6 marks

Desribe structure of DNA and chromosomes

Answer 21

DNA structure
* A nucleotide has a deoxyribose sugar, a phosphate and nitrogenuous base
* Backbone is joined by phosphodiester bonds
* Adenine, guanine, cytosine and thymine bases are joined by hydrogen bonds (A-T, G-C) - complementary base pairs
* Double helix formed (antiparallel)

Chromosome structure
* DNA associated with histone proteins
* 2 identical chromatids joined by a centromere

Question 22

4 marks

Describe and explain meoisis that result in genetic variation within a species

Answer 22

• In metaphase I of meoisis crossing over between homologous pairs= variation in gametes
• Also in metaphase I independent segration of the homologous pairs leads to variation of different alleles in the gametes
• Random fertlisation of gametes
• New combination of alleles in gametes

Question 23

4 marks

Use your knowledge of natural selection to explain why resistance is so common in Africa

Answer 23

1. Random genetic mutation for allele for the resistance
2. This beneficial allele leads to survival of the fittest and they are more likely to survive
3. They breed and pass on the allele
4. Allele frequency increases over many generations

Question 24

5 marks

Natural selection

Answer 24

1. Variation happens when new alleles are generated by random genetic mutations
2. A new selection pressure of a predator creates a struggle for survival
3. Those will beneficial alleles are best adaptred to selection pressure and survive
4. They breed and pass on these beneficial alleles
5. Next generation will have a higher fequency if beneficial alleles in gene pool

Question 25

Explain antibiotic resistance

Answer 25

1. Frequent use of antibiotic creates selection pressure
2. Bacteria with mutation are more likely to survive
3. Reproduce more than other types ad pass of beneficial allele to offspring
4. Frequency of beneficial allele increases in subsequent generations
5. Frequency of resistant types increases in subsequent generations

Question 26

4 marks

Desrcibe aseptic tecnhiques

Answer 26

1. Disinfect surface prior to the investigation
2. Use a sterile spreader
3. Have a bunsen burner close to work space to create convection current to remove microoraginism upwards
4. Flaming neck of the bottle
5. Slightly lifiting lid of algar plate to avoid contiminates getting in

Question 27

One farmer stated that the increase in the use of Bt crop plants had caused a mutation
in one of the insect species to become resistant to the toxins in the plants and that this mutation had spread to other species of insect. Was he correct? Explain your answer.

Answer 27

1. Mutations are spontaneous/random;
2. Only the rate of mutation is affected by environment;
3. Different species do not interbreed/do not produce fertile offspring;
4. So mutation/gene/allele cannot be passed from one species to another;

Question 28

2 marks

During courtship males of a bird species vibrate their wings which produces a sound.
Explain how this sound helps to ensure that the female mates only with a male of the same species.

Answer 28

• Female recognises own species sound
• Respond to that soundy only
• Courtship sequence continues

Question 29

1 mark

Define phylogenetic classification

Answer 29

Grouped according on evolutionary orgins.

Question 30

1 mark

Define heirachy

Answer 30

Smaller groups within larger groups with no overlap

Question 31

2 marks

Describe how organisms are grouped in a phylogenetic classification system.

Answer 31

1. Heirachy (smaller groups within larger groups) with no overlap
2. Grouped according to evolutionary origins

Question 32

5 marks

Haemoglobins are chemically similar molecules found box in many different species.
Differences in the primary structure of haemoglobin molecules can provide evidence of phylogenetic (evolutionary) relationships between species.
Explain how.

Answer 32

1. Mutations change bases
2. Change in amino acid sequence
3. Mutations build up over time
4. More mutations =more differences in amino acid sequence between distantly related species;
5. Distantly related species have earlier common ancestor

Question 33

2 marks

Explain why temperatures could be used to fine the % of DNA hybridisation

Answer 33

Higher temperature= more energy required= the higher the percentage DNA hybridisation = more bases are similar
Correct reference to breaking hydrogen bonds / more/less hydrogen bonds being present;

Question 34

2 marks

Explain why biologists use protein structure to investigate the realtionship between different species of cranes.

Answer 34

1. More closely related species have more similarities in amino acid sequence
2. In same protein
3. Amino acid sequence is related to DNA base/triplet sequence;