AQA Biology A-level Topic 4 Practice Flashcards

A set of practice flashcards covering definitions and concepts for AQA Biology A-level Topic 4: Genetic Information, Variation and Relationships between Organisms.

What are the three categories of adaptations an organism may possess?

Adaptations may be anatomical, physiological or behavioural.

What is an allele?

A version of a gene.

What is an anticodon?

A sequence of three nucleotide bases at one end of a tRNA molecule that is specific to an mRNA codon.

How is the arithmetic mean calculated?

By dividing the sum of the values by the number of values.

On what criteria does artificial classification base its groupings?

Analogous characteristics such as leaf shape, number of legs and type of wing.

What are the two components of the binomial system of naming organisms?

The generic name and the specific name (e.g. Homo sapiens).

What are the three levels of variety described by biodiversity?

The variety of genes, species and habitats within a particular area.

What is the cellular proteome?

The proteins expressed in a given type of cell.

What is a chromatid?

One strand of a replicated chromosome.

What is a chromosome?

A structure consisting of a long, coiled molecule of DNA and its associated proteins, by which genetic information is passed from generation to generation.

What constitutes a chromosome mutation?

A change to the number or structure of chromosomes that can occur spontaneously.

What are the two types of classification of organisms?

Artificial and phylogenetic.

What is a codon?

A sequence of three bases on mRNA that codes for a specific amino acid.

What is the definition of conservation?

The maintenance of ecosystems and biodiversity by humans in order to preserve the Earth's resources.

What are the functions of courtship behaviour?

It enables organisms to recognise their own species, identify a mate with a capacity to breed, form a pair bond, synchronise mating and become able to breed themselves.

What happens during the process of crossing over?

In meiosis 1, homologous chromosomes pair up, chromatids wrap around one another, and alleles are exchanged at equivalent portions to create genetic variation.

What does it mean for the genetic code to be 'degenerate'?

More than one triplet can code for a particular amino acid.

How can a deletion mutation affect a protein?

One or more nucleotide bases are removed, which may change all amino acids in a sequence and render the protein non-functional.

What is directional selection?

A type of selection that favours individuals that differ in one direction (fall to the left or the right) from the population mean, changing the population's traits.

What is ecosystem diversity?

A measure of the range of different habitats in a particular area.

Contrast eukaryotic nuclear DNA with DNA found in mitochondria and chloroplasts.

Nuclear DNA is linear and associated with histones; mitochondrial and chloroplast DNA is circular and lacks associated proteins.

What is an exon?

A sequence of DNA that codes for an amino acid sequence.

What is the result of fertilisation in terms of ploidy and variation?

The random fusion of haploid gametes produces a diploid zygote and mixes genetic information to create genetic variation.

What is a gene?

A length of DNA on a chromosome that codes for the production of one or more polypeptide chains and functional RNA.

When do gene mutations typically occur?

Spontaneously during DNA replication.

What does the generic name in binomial nomenclature denote?

The organism's genus.

What are the three defining features of the genetic code?

The genetic code is degenerate, universal and non-overlapping.

How is genetic diversity defined?

The number of different alleles in a population.

What is a genome?

The entire set of genes in a cell.

What are histones?

Proteins that, together with DNA, form chromosomes in the nuclei of eukaryotic cells.

What are homologous chromosomes?

A chromosome pair, one paternal and one maternal, with the same gene loci.

What is independent segregation?

The random separation of homologous chromosomes in meiosis 1 that produces genetic variation.

What is the formula for the index of diversity ($d$)?

$$d = \frac{N(N-1)}{\sum n(n-1)}$$

In the index of diversity formula, what do $N$ and $n$ represent?

$N$ is the total number of organisms of all species and $n$ is the total number of organisms of each species.

What is an intron?

A non-coding sequence of DNA.

Where is a gene's locus located?

On the chromosome at a specific position.

What does the mean represent on a normal distribution curve?

A measure of the maximum height of the curve.

What is the result of meiosis?

Four genetically different daughter cells (gametes) with a haploid number of chromosomes.

Describe the structure and function of messenger RNA (mRNA).

A single helix of thousands of mononucleotides that carries genetic information from the nucleus to ribosomes.

What is the result of mitosis?

Two genetically identical diploid daughter cells.

What is a mutagenic agent?

An agent that increases the rate of gene mutations above normal level.

What is natural selection?

The process where the frequency of 'advantageous' alleles gradually increases in a population's gene pool over time.

What are two examples of non-coding sequences in eukaryotic nuclear DNA?

Repeating base sequences and introns.

What is chromosomal non-disjunction?

The failure of homologous chromosomes to separate during meiosis, potentially resulting in gametes with one more or one less chromosome.

What does the term 'non-overlapping' mean in relation to genetic triplets?

Each base in a sequence is read once and is only part of one triplet.

On what criteria is phylogenetic classification based?

Evolutionary relationships and homologous characteristics.

What is phylogeny?

The evolutionary relationships between individuals or groups of organisms.

What are the characteristics of prokaryotic DNA?

Circular pieces of DNA that do not have associated proteins.

What is the purpose of random sampling?

To avoid bias, for example by using a square grid and generating random coordinates.

What is recombination?

When broken-off pieces of chromatid combine with another chromatid on a different chromosome during crossing over.

What is the structure of a ribosome?

A sub-cellular structure consisting of a small subunit and a large subunit.

What is the role of RNA polymerase in protein synthesis?

It moves along the DNA template strand and joins adjacent nucleotides to form pre-mRNA.

How is a species defined?

A group of similar organisms that are able to breed with one another to produce living, fertile offspring.

What is species diversity?

A measure of the number of different species and the abundance of individuals in each of those species within a community.

What is species richness?

A measure of the number of different species in a community at a given time.

How is the specific name of an organism formatted in the binomial system?

It denotes the species and is written in lower case letters (e.g. sapiens).

What occurs during splicing?

Introns are removed from pre-mRNA and exons are joined together to form mRNA in eukaryotic cells.

What is stabilising selection?

A type of selection that favours individuals close to the mean, maintaining the traits of the population.

What does standard deviation indicate about a population?

The width of a normal distribution curve and the range of values.

What is a substitution mutation?

One nucleotide base is exchanged for another, which may change an amino acid or produce the same one due to code degeneracy.

What is a taxon?

Each group within a phylogenetic classification system.

What is transcription?

The first stage of protein synthesis; the formation of pre-mRNA (eukaryotes) or mRNA (prokaryotes) from a section of DNA.

Describe the structure of transfer RNA (tRNA).

Single-stranded, clover-leaf shape, with one end for amino acid attachment and the opposite end containing an anticodon.

What is translation?

The second phase of protein synthesis where mRNA acts as a template for tRNA molecules to join amino acids into a polypeptide chain.

What is a triplet?

A sequence of three bases that codes for an amino acid.

Why is the universal nature of the genetic code evidence for evolution?

Because the code is the same in almost all organisms.

What causes variation between individuals?

Genes, the environment, or a combination of both.