BIG IDEAS 1-3 (Key Definition)

Genome

The complete set of genetic information (DNA) in an organism.

Chromosome

A long, coiled DNA molecule containing many genes.

DNA

A double helix-shaped molecule that stores genetic information in the sequence of its bases, providing the instructions for an organism's form and function.

Gene

A sequence of DNA that codes for a protein that contributes to an organism's phenotype (observable characteristic).

Allele

A different version of a gene caused by a difference in its DNA base sequence.

Note: can result in different phenotype

Mutation

A permanent random change in the DNA base sequence. The only source of new alleles.

Protein

A molecule produced from the instructions in a gene that carries out a specific function and influences characteristics.

Inheritance

The passing of genetic information (alleles) from parents to offspring.

Heritable characteristic

A characteristic determined by alleles in the genotype that can be passed from parents to offspring because the alleles are present in the gametes (sex cells).

Non-inheritable characteristic

A characteristic that results from the environment interacting with the genotype of somatic (body) cells and cannot be passed to offspring because the alleles in the gametes are unchanged.

Fertilisation

The fusion of a sperm and egg cell to form a zygote.

Zygote

The first cell formed when a sperm fertilises an egg.

Genotype

The combination of alleles an organism has for a gene.

Homologous Pair

A pair of chromosomes, one inherited from each parent, that contain the same genes in the same locations but may carry different alleles.

Phenotype

The observable characteristics (traits) of an organism resulting from the interaction between its genotype and environmental factors.

Dominant allele

An allele that is expressed in the phenotype when at least one copy is present.

Recessive allele

An allele that is expressed in the phenotype only when two copies are present.

Homozygous

Having two identical alleles for a gene.

Heterozygous

Having two different alleles for a gene.

Carrier

A heterozygous individual who carries a recessive allele without expressing the recessive phenotype.

Complete dominance

A pattern of inheritance in which one allele completely masks the expression of the other in a heterozygous individual.

Gamete

A haploid sex cell (sperm or egg) containing one allele for each gene.

Gametic mutation

A mutation that occurs in a gamete or the cells that produce gametes can be inherited by offspring if fertilised.

Somatic mutation

A mutation that occurs in a body cell and cannot be inherited by offspring.

Meiosis

A type of cell division that produces four genetically different haploid gametes.

Segregation

The separation of two alleles of a gene during meiosis so that each gamete receives one allele.

Independent assortment

Different chromosome pairs separate independently, producing different combinations of maternal and paternal chromosomes in each gamete.

Crossing over

Homologous chromosomes exchange sections of DNA, producing new combinations of alleles.

Sexual reproduction

Reproduction involving the fusion of genetically unique gametes from two parents, producing offspring with a unique combination of alleles.

Random fertilisation

The random fusion of one genetically unique sperm and one genetically unique egg, producing a unique combination of alleles in the offspring.

Genetic variation

The range of alleles and allele combinations within a population, or between different populations.

Gene pool

All the alleles present within a population.

Allele frequency

The proportion of a particular allele within a population.

Migration (gene flow)

The movement of individuals into or out of a population, introducing or removing alleles from the gene pool.

Non-random mating

Mating in which individuals do not choose mates by chance, some individuals are more likely to mate than others, influencing genotype frequencies and sometimes allele frequencies.

Sexual selection (mate choice)

A type of non-random mating in which individuals with certain inherited characteristics are more likely to obtain mates and reproduce.

Inbreeding

A type of non-random mating between closely related individuals that increases homozygosity and reduces genetic variation.

Artificial selection

A type of non-random mating in which humans select individuals to reproduce to increase the frequency of desired inherited characteristics or maintain genetic variation.

Differing rates of survival (natural selection)

Individuals with phenotypes that are better suited to their environment are more likely to survive and reproduce. Over generations, the alleles responsible for these phenotypes become more common in the population.

Genetic drift

Random changes in allele frequencies due to chance, particularly in small populations.

Adaptation

An inherited characteristic that increases an individual's survival and reproductive success in a particular environment.

Population

A group of individuals of the same species living in the same area, at the same time and can interbreed.

Resilience

The ability of a population to survive, reproduce and adapt to environmental change.

Gene tracking

The process of following a (specific) gene through generations of organisms or tracing it in individuals within or between populations.

Pedigree analysis

A method that uses a family tree to trace the inheritance of alleles through generations and infer genotypes.

DNA profiling

A method that compares selected genetic markers to identify individuals, determine biological relationships and compare genetic variation.

DNA sequencing

A method that determines the exact order of DNA bases to identify alleles, mutations, and genetic variation.

Genome analysis

A method that compares the complete genome of individuals or populations to identify genetic relationships and patterns of genetic variation.

Genetic marker

A known DNA sequence that varies between individuals and can be used to identify alleles, individuals or genetic relationships.

Biological relationship

The degree to which individuals are genetically related through shared DNA inherited from common ancestors.

Biological evidence

Information collected through observations, investigations or gene-tracking methodologies that is used to explain or support biological conclusions.