Genetics Glossary

Glossary:

DNA Structure
The double-helix structure of DNA enabling it to act as a
stable information-carrying molecule, in terms of the
components of DNA nucleotides: deoxyribose, phosphate
and the bases adenine, cytosine, guanine and thymine; two
sugar-phosphate backbones held together by hydrogen bonds
between base pairs; specific base pairing. DNA is the genetic
material in bacteria as well as in most other organisms.
Analyse, interpret and evaluate data concerning early
experimental work relating to the role and importance of
DNA.

DNA Replication
The semi-conservative replication of DNA in terms of:
breaking of hydrogen bonds between polynucleotide strands;
attraction of new DNA nucleotides to exposed bases and
base pairing; role of DNA helicase and of DNA polymerase.

Gene Expression
Genes are sections of DNA that contain coded information
as a specific sequence of bases. A gene occupies a fixed
position, called a locus, on a particular strand of DNA.
Genes code for polypeptides that determine the nature and
development of organisms. The base sequence of a gene
determines the amino acid sequence in a polypeptide. A
sequence of three bases, called a triplet, codes for a specific
amino acid.

In eukaryotes, much of the nuclear DNA does not code for
polypeptides. There are, for example, introns within genes
and multiple repeats between genes.

Mutations
Mutations are changes in DNA and result in different
characteristics. Differences in base sequences of alleles of a
single gene may result in non-functional proteins, including
non-functional enzymes.

Chromosomes
In eukaryotes, DNA is linear and associated with proteins. In
prokaryotes, DNA molecules are smaller, circular and are
not associated with proteins.

Mitosis and the Cell Cycle
During mitosis, the parent cell divides to produce two
daughter cells, each containing an exact copy of the DNA ofthe parent cell. DNA is replicated during interphase. Mitosis
increases the cell number in this way in growth and tissue
repair. Name and explain the events occurring during each
stage of mitosis. Recognise the stages from drawings and
photographs. Relate understanding of the cell cycle to cancer
and its treatment.

Meiosis and Sexual Reproduction
The importance of meiosis in producing cells which are
genetically different. Meiosis only in sufficient detail to show
the formation of haploid cells; independent segregation of
homologous chromosomes; and genetic recombination by
crossing over. Gametes are genetically different as a result of
different combinations of maternal and paternal
chromosomes.

Cell Differentiation
The cells of multicellular organisms may differentiate and
become adapted for specific functions. Tissues as
aggregations of similar cells, and organs as aggregations of
tissues performing specific physiological functions. Organs
are organised into systems.

Antibiotics and Resistance
Antibiotics may be used to treat bacterial disease. One way
in which antibiotics function is by preventing the formation of
bacterial cell walls, resulting in osmotic lysis. Mutations in
bacteria may result in resistance to antibiotics. Resistance to
antibiotics may be passed to subsequent generations by
vertical gene transmission. Resistance may also be passed
from one species to another when DNA is transferred
during conjugation. This is horizontal gene transmission.

Antibiotic resistance in terms of the difficulty of treating
tuberculosis and MRSA. Apply the concepts of adaptation
and selection to other examples of antibiotic resistance.
Evaluate methodology, evidence and data relating to
antibiotic resistance. Discuss ethical issues associated with
the use of antibiotics. Discuss the ways in which society uses
scientific knowledge relating to antibiotic resistance to
inform decision-making.

Classification
A species may be defined in terms of observable similarities
and the ability to produce fertile offspring. Candidates should
appreciate the difficulties of defining species and the tentative
nature of classifying organisms as distinct species.

The principles and importance of taxonomy. Classification
systems consist of a hierarchy in which groups are contained
within larger composite groups and there is no overlap. One
hierarchy comprises Kingdom, Phylum, Class, Order, Family,
Genus, Species. The phylogenetic groups are based on
patterns of evolutionary history.

Originally classification systems were based on observable
features but more recent approaches draw on a wider range
of evidence to clarify relationships between organisms.
Genetic comparisons can be made between different species
by direct examination of their DNA or of the proteins
encoded by this DNA.
• Comparison of DNA base sequences is used to elucidate
relationships between organisms. These comparisonshave led to new classification systems in plants.
Similarities in DNA may be determined by DNA
hybridisation.
• Comparisons of amino acid sequences in specific proteins
can be used to elucidate relationships between
organisms. Immunological comparisons may be used to
compare variations in specific proteins.
Interpret data relating to similarities and differences in base
sequences in DNA and in amino acid sequences in proteins
to suggest relationships between different organisms.

The role of courtship in species recognition. Courtship
behaviour as a necessary precursor to successful mating.