Genetic Information, Variation and Relationships Between Organisms

What is a gene?

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

What is a genome?

The complete set of genetic material in an organism.

What is a proteome?

The complete set of proteins expressed by a genome, cell, tissue or organism.

What is a chromosome?

A DNA molecule associated with proteins.

What is a locus?

The specific position of a gene on a chromosome.

What is an allele?

An alternative form of a gene.

What is the genetic code?

The sequence of base triplets that determines the amino acid sequence of a polypeptide.

What is a codon?

A sequence of three bases on mRNA that codes for an amino acid or stop signal.

Why is the genetic code described as universal?

The same codons specify the same amino acids in almost all organisms.

Why is the genetic code described as degenerate?

Most amino acids are coded for by more than one codon.

Why is the genetic code non-overlapping?

Each nucleotide is read as part of only one codon.

What is transcription?

The synthesis of RNA using a DNA template.

Where does transcription occur in eukaryotic cells?

The nucleus.

What is the role of RNA polymerase?

Joins RNA nucleotides to form an RNA strand complementary to the DNA template.

What happens during transcription?

DNA unwinds, RNA nucleotides pair with the template strand and RNA polymerase joins them.

What is pre-mRNA?

The initial RNA transcript produced during transcription in eukaryotes.

What are introns?

Non-coding sections of pre-mRNA removed during splicing.

What are exons?

Sections of pre-mRNA retained in mature mRNA.

What is RNA splicing?

Removal of introns and joining of exons to form mature mRNA.

What is translation?

The synthesis of a polypeptide using the codon sequence of mRNA.

Where does translation occur?

At ribosomes.

What is an anticodon?

A sequence of three bases on tRNA complementary to an mRNA codon.

What is the role of tRNA in translation?

Delivers specific amino acids to the ribosome.

What happens during translation?

tRNA anticodons pair with mRNA codons and amino acids are joined by peptide bonds.

What is a start codon?

A codon that signals the beginning of translation.

What is a stop codon?

A codon that signals the end of translation.

What is a mutation?

A change in the nucleotide sequence of DNA.

What is a substitution mutation?

One nucleotide is replaced by another.

What is an insertion mutation?

One or more nucleotides are added to a DNA sequence.

What is a deletion mutation?

One or more nucleotides are removed from a DNA sequence.

What is a frameshift mutation?

A mutation that changes the reading frame of codons.

Why can insertions and deletions cause major changes to proteins?

They can alter all subsequent codons if the number of bases changed is not a multiple of three.

Why might a substitution mutation have no effect?

The new codon may code for the same amino acid.

How can a mutation affect protein structure?

It may change the amino acid sequence, altering bonding and folding.

What is a mutagen?

A factor that increases the rate of mutation.

Give examples of mutagens.

Ionising radiation, ultraviolet radiation and some chemicals.

What is meiosis?

A type of cell division producing genetically different haploid cells.

What is a haploid cell?

A cell containing one set of chromosomes.

What is a diploid cell?

A cell containing two sets of chromosomes.

What are homologous chromosomes?

A pair of chromosomes with the same genes at the same loci but potentially different alleles.

What happens during meiosis I?

Homologous chromosomes separate, reducing chromosome number by half.

What happens during meiosis II?

Sister chromatids separate.

What is crossing over?

Exchange of DNA between non-sister chromatids of homologous chromosomes.

When does crossing over occur?

Prophase I of meiosis.

How does crossing over increase genetic variation?

It produces new combinations of alleles on chromosomes.

What is independent segregation?

Random separation of homologous chromosome pairs during meiosis I.

How does independent segregation increase genetic variation?

It produces different combinations of maternal and paternal chromosomes in gametes.

How does random fertilisation increase genetic variation?

Any male gamete can fuse with any female gamete, producing different allele combinations.

What is genetic diversity?

The number of different alleles of genes in a population.

What is a gene pool?

All the alleles present in a population.

What is an allele frequency?

The proportion of a particular allele in a population.

What is natural selection?

A process in which individuals with advantageous inherited characteristics are more likely to survive and reproduce.

What is directional selection?

Selection favouring one extreme phenotype.

What is stabilising selection?

Selection favouring intermediate phenotypes.

How does natural selection change allele frequencies?

Advantageous alleles become more common because their carriers reproduce more successfully.

What is a selection pressure?

An environmental factor that affects survival and reproductive success.

How does antibiotic resistance develop in bacteria?

Resistance mutations arise randomly; antibiotics kill susceptible bacteria, leaving resistant bacteria to reproduce.

Why does antibiotic use increase the frequency of resistance alleles?

It acts as a selection pressure favouring resistant bacteria.

What is a species?

A group of organisms capable of interbreeding to produce fertile offspring.

What is taxonomy?

The science of classifying organisms.

What is the purpose of classification?

To organise organisms according to similarities and evolutionary relationships.

What is the hierarchy of classification?

Domain, kingdom, phylum, class, order, family, genus and species.

What is binomial nomenclature?

A naming system using genus and species names.

What are the three domains?

Bacteria, Archaea and Eukarya.

What is phylogenetic classification?

Classification based on evolutionary relationships and common ancestry.

What is a phylogenetic tree?

A diagram showing evolutionary relationships between organisms.

How can DNA sequences be used to determine evolutionary relationships?

More similar DNA sequences suggest a more recent common ancestor.

How can amino acid sequences be used to determine evolutionary relationships?

More similar sequences suggest organisms are more closely related.

What is biodiversity?

The variety of living organisms in an area.

What is species richness?

The number of different species present in a community.

What is an index of diversity?

A measure considering both the number of species and the number of individuals in each species.

What is the AQA index of diversity formula?

d = N(N − 1) ÷ Σn(n − 1).

What does N represent in the index of diversity formula?

The total number of organisms of all species.

What does n represent in the index of diversity formula?

The number of organisms of one particular species.

What does a higher index of diversity indicate?

Greater species diversity.

Why is biodiversity important?

It contributes to ecosystem stability and provides genetic resources.

How can farming reduce biodiversity?

By removing habitats, using pesticides and growing monocultures.

What is a monoculture?

The cultivation of one crop species over a large area.

Why can monocultures reduce biodiversity?

They reduce habitat variety and available food sources.

What is conservation?

The protection and management of species and habitats to maintain biodiversity.

What is random sampling?

Selecting samples so every location has an equal chance of selection.

Why is random sampling important?

It reduces sampling bias.

What is a quadrat?

A frame used to sample organisms within a defined area.

What is a transect?

A line or belt along which organisms are sampled to investigate distribution.

What is the difference between random and systematic sampling?

Random sampling uses chance; systematic sampling follows a fixed pattern.

What is a population?

All organisms of one species living in a particular area at a particular time.

What is a community?

All populations of different species living in an area.

What is an ecosystem?

A community of organisms interacting with each other and their physical environment.

What is intraspecific variation?

Differences between individuals of the same species.

What is interspecific variation?

Differences between individuals of different species.

What causes genetic variation?

Mutations, meiosis and random fertilisation.

What causes environmental variation?

Differences in environmental conditions.

What is continuous variation?

Variation showing a range of values with no distinct categories.

What is discontinuous variation?

Variation showing distinct categories with no intermediate values.

What is standard deviation?

A measure of how spread out data values are around the mean.

What does a large standard deviation indicate?

Data values are widely spread around the mean.

What is a normal distribution?

A symmetrical bell-shaped distribution where most values occur near the mean.

What is the null hypothesis?

A statement that there is no significant difference or association between variables.

What is the purpose of a statistical test?

To determine whether observed results are statistically significant.

What is the chi-squared test used for?

Testing whether observed frequencies differ significantly from expected frequencies.