2BIO Genetic Expression and Variation

Directional Selection

A type of natural selection where an environmental pressure favours individuals at one extreme of a phenotypic range.

Stabilising Selection

A type of natural selection in which environmental pressure favours individuals of an average or intermediate phenotypic range over extremes.

Segregation

Allele pairs separate during the formation of reproductive cells, ensuring each gamete only receives one allele.

Mate Selection

An evolutionary process where a sex (usually females) chooses a specific partner from the opposite sex based on desirable traits.

Selective Pressure

Any external environmental factor that reduces or increases reproductive success in a population, driving natural selection and evolution.

Disruptive Selection

A type of natural selection that favours individuals with extreme traits over those of average or intermediate phenotypic ranges.

Independent Assortment

A biological principle stating that the alleles of different genes segregate into gametes independently of one another.

DNA Polymerase

Synthesises new DNA strands by adding free nucleotides to a complementary template DNA strand.

RNA Polymerase

Synthesises an RNA strand during transcription, which is edited to become the mRNA strand used in translation.

Endoplasmic Reticulum

Folds, modifies and transports proteins and lipids.

Enzymes

Globular proteins that act as biological catalysts, speeding up metabolic reactions without being used up in the process.

Golgi Body

An organelle that modifies, sorts and packages proteins and lipids for storage or transport out of the cell.

Nuclear Envelope

A double membrane barrier that surrounds the nucleus, protecting the genetic information that it stores from damage by reactive chemicals and destructive enzymes that reside inside the cytoplasm.

Purine

A double-ringed structure, either Adenine or Guanine, only bonds with the single-ringed structure.

Pyrimidine

A single-ringed structure, either Cytosine, Thymine or Uracil, only bonds with the double-ringed structure.

Two reasons for using mRNA in Translation over DNA

Keep DNA protected from damage inside the nucleus; allows for faster protein synthesis, as multiple mRNA strands can be translated at a time, and more mRNA strands can be formed during translation.

Purpose for Transcription

Copy genetic instruction from the DNA strand into a portable messenger (mRNA). Protects DNA from damage, by allowing it to remain safe in the nucleus.

Purpose for Translation

To convert the genetic code carried by the mRNA molecule into its specific sequence of amino acids, creating a polypeptide chain. To build into a functional protein.

Protein Synthesis

The biological processes involved in the creation of a protein from genetic information to express a trait, has two main stages transcription and translation.

Sole source of new alleles

Mutations

Significance of Proteins

Essential molecules that perform most of the critical work inside living cells, driving the structure, function and regulation of all tissues and organs.