Genetic information, variation and relationships between organisms

Question 1

Describe the non-coding and coding parts of DNA

Answer 1

• Introns = these are base sequences present within genes but do not code for amino acids
• Multiple repeats = some of the base sequences present between genes that consists of the same base sequence occurring again and again
• Exons = base sequences in genes that code for amino acids

Question 2

Describe the 3 features of the genetic code

Answer 2

Degenerate = more than one triplet codes for the same amino acid
Non-overlapping = each base is only read once as part of a specific triplet
Universal = the same triplets code for the same amino acids in all organisms

Question 3

Define what is meant by a base triplet

Answer 3

A sequence of three nucleotide bases that codes for a specific amino acid - base ‏‎triplets in mRNA are specifically referred to as codons

Question 4

Define what is meant by gene

Answer 4

Sequence of DNA bases that code for the specific amino acid sequence of a polypeptide ‏‏‎and for functional RNA (including ribosomal RNA and tRNAs)

Question 5

Describe how chromosomes are formed

Answer 5

Formed by DNA and histones during cell division

Question 6

Compare DNA in prokaryotic cells and eukaryotic cells

Answer 6

In prokaryotic cells: shorter, circular and not associated with proteins
Where in eukaryotic cells: longer, linear and associated with proteins

Question 7

Describe the process of translation

Answer 7

• mRNA binds to ribosomes
• tRNA anticodons bind to complementary codons on mRNA strand
• tRNA brings a specific amino acid to the ribosome and amino acids are then joined together by peptide bonds with the use of ATP
  tRNA released and the ribosome moves along the mRNA to form the polypeptide

Question 8

Describe the difference between transcription in prokaryotes and eukaryotes

Answer 8

In prokaryotes, transcription results directly in the production of mRNA from DNA
In eukaryotes, transcription results in the production of pre-mRNA - this is then spliced to form mRNA

Question 9

Describe the process of transcription

Answer 9

• Hydrogen bonds between DNA bases break
• One DNA strand acts as a template strand
  ‎‎‎- Free RNA nucleotides align by complementary base pairing (uracil used instead of thymine)
• RNA polymerase joins adjacent RNA nucleotides by phosphodiester bonds
• This forms pre-mRNA which is then spliced (removal of introns) to form mRNA

Question 10

Define what is meant by proteome

Answer 10

Full range of proteins that a cell is able to produce

Question 11

Define what is meant by genome

Answer 11

Complete set of genes (and the non-coding DNA) in a cell

Question 12

Compare the structures of mRNA and tRNA

Answer 12

mRNA is linear, possesses codons and has no hydrogen bonds or anticodon binding site.
tRNA is clover leaf shaped, possesses anticodons and has both an anticodon binding site and hydrogen bonds.

Question 13

Describe what is meant by gene mutations and the different types of mutations

Answer 13

Gene mutations are changes in the sequence of nucleotide bases in the DNA
- Substitution: replacement of one or more bases by one or more different bases
- Deletion: removal of one or more bases
- Addition: adding of one or more bases
- Duplication: where one or more bases is repeated

Question 14

Describe why some mutations cause a non-functional protein to be produced

Answer 14

Mutations result in frame shift - alteration in base triplets from the point of mutation e.g. addition
The sequence of amino acids is altered from the point of mutation and the protein formed is functional

Question 15

Describe why not all base substitutions cause a change in the encoded amino acids

Answer 15

Due to the degeneracy of the genetic code which means the new base triplet could code ‎‏‏for the same amino acid

Question 16

Describe what mutagenic agents are used for

Answer 16

Increase the rate of mutation e.g. benzene, X-rays

Question 17

Describe how mutations in the number of chromosomes can arise

Answer 17

By chromosome non-disjunction during meiosis

Question 18

State the different types of adaptations that arise from natural selection

Answer 18

Anatomical e.g. bigger beaks for eagles
Physiological e.g. snakes and spiders produce venom to paralyse their prey and make them easier to digest
Behavioural e.g. bears hibernate in the winter to conserve energy as there is less food

Question 19

Describe stabilising selection with the example of human birth weights

Answer 19

• Stabilising selection occurs when the environment remains stable and selection occurs towards organisms with a phenotype closest to the mean (the “norm”)
• Natural selection favours those organisms with alleles for characteristics towards the middle of the birth mass range.
• These organisms survive to breed and pass on their alleles to the next generation.
• So the frequency of alleles for optimal birth mass tends to remain stable over generations
  Babies with alleles for the extremes of this range i.e. very high or very low birth masses have a higher mortality rate and fewer survive to breed and pass on their alleles to the next generation

Question 20

Describe directional selection with the example of antibiotic resistance in bacteria

Answer 20

• Directional selection occurs when there is a change in an environment e.g. antibiotic resistance in bacteria
• Due to random mutations a few bacteria in a population possess an allele which provides resistance against a particular antibiotic
• The use of this antibiotic against this species of bacterium would provide a selection pressure
• Bacteria with the antibiotic resistant allele would survive and reproduce by binary fission to pass on the allele for antibiotic resistance to the next generation
• Most non-resistant bacteria will be killed and so fewer reproduce and their frequency in the population decreases over generations.
• The frequency of antibiotic resistant bacteria and the frequency of the allele for antibiotic resistance would significantly increase in the population over generations

Question 21

Describe the principles of natural selection in evolution of species

Answer 21

• Random mutation can result in new alleles of a gene
• The new allele of a gene might benefit its possessor, leading to increased reproductive success
• The advantageous allele is inherited by members of the next generation
• As a result, over many generations the new allele increases in frequency in the population

Question 22

Describe what is meant by genetic diversity and its importance

Answer 22

Genetic diversity is the number of different alleles in a population
Importance = enables natural selection to occur

Question 23

Describe how species are universally identified

Answer 23

By a binomial consisting of Genus and Species e.g. Homo Sapiens

Question 24

State the order of classification

Answer 24

Domain
Kingdom
‎Phylum
Class
Order
Family
Genus
Species

Question 25

Describe the phylogenetic classification system

Answer 25

Attempts to arrange species into groups based on their evolutionary origins and relationships It uses a hierarchy in which smaller groups are placed within larger groups, with no overlap between groups Each group is called a taxon (plural taxa)

Question 26

Describe the role of courtship in species recognition

Answer 26

Allows individuals to: Recognise members of their own species Recognise members of the opposite sex Identify a mate who is capable of breeding (i.e. sexually mature, fertile and biologically fit).

Question 27

Describe how you would identify organisms that belong to the same species

Answer 27

Two organisms belong to the same species if they are able to produce fertile offspring

Question 28

Describe what can reduce biodiversity

Answer 28

- Deforestation and farming practices (such as large areas of land being used to grow single crops) - This occurs due to a: 1. decrease in the variety of plant species 2. decrease in the number and variety of habitats 3. decrease in the variety of food sources 4. decrease in animal diversity

Question 29

Describe the use of index of diversity

Answer 29

Describes the relationship between the number of species in a community and the‎‏‏‎ ‏‏‎‎‏‏number of individuals in each species

Question 30

Describe what is meant by species richness

Answer 30

Measure of the number of different species in a community

Question 31

Describe what is meant by biodiversity

Answer 31

It refers to the number and variety of living organisms in a particular area Biodiversity can relate to a range of habitats, from a small local habitat to the Earth

Question 32

How can we investigated biodiversity within or between species

Answer 32

- The frequency of measurable or observable characteristics (dividing the area into a grid and using a random number generated to take samples in an area) - The amino acid sequence of the proteins encoded by DNA and mRNA - The base sequence of DNA - The base sequence of mRNA - The more closely related species/organisms are, the more similar their genetic sequences are

Question 33

Interspecific

Answer 33

between organisms of different species

Question 34

Infraspecific

Answer 34

within species between organisms

Question 35

Substitutions and changes to the polypeptide structure

Answer 35

Not all substitution mutations will result in a change to the amino acid sequence of a protein due to the degenerative nature of the genetic code. However it can cause different amino acids to be encoded causes changes to primary and therefore tertiary structures of proteins due to the difference in where bonds e.g. hydrogen and ionic bonds occur.

Question 36

Deletions and changes to the polypeptide structure

Answer 36

cause a frameshift where the entire sequence after the deletion shifts to the left by one base this changes all the triplets after the deletion and so also changes the amino acid sequence.

Question 37

Insertions and changes to the polypeptide structure

Answer 37

This causes a frameshift where the entire sequence after the insertion shifts to the right by one base. This changes all the triplets after the insertion and so also changes the amino acid sequence.

Question 38

Polyploidy

Answer 38

This is when organisms have more than two sets of chromosomes, and is mostly seen in plants.

Question 39

Non-disjunction

Answer 39

This occurs when homologous chromosomes fail to separate in meiosis, resulting in gametes with extra or missing chromosomes, and leads to individuals with extra or missing chromosomes in all cells.