genetic variation

Variation

Differences of traits within a population. It can be inherited or environmental (non-inherited)

Mutation

Permanent change in the genetic code of an organism and are the source of all new variation in a gene pool

Meiosis

Specialised type of cell division that only occurs in sex organs to produce sex cells. Division results in 4 daughter cells, each containing half the number of chromosomes and are genetically unique.

Sexual Reproduction

When male gametes (sperm) are transferred to the female gametes (egg) for fertilisation and the production of new offspring that are genetically unique from their parents

Gametes

Sex cells or sperm (male) and egg or ova (female) and are only found in sex organs (males-testes; females - ovaries). Have half the number of chromosomes and a mutation in these cells could be passed on to future generations and enter the gene pool

Somatic Cells

General body cells that make up all tissues in the body and are formed by mitosis, they have a full set of chromosomes. A mutation in this type of cell will not be passed on to future generations

Crossing Over

When homologous chromosomes pair at the start of meiosis they often get tangled and sections can break off and swap with the other chromosome (alleles are exchanged). This results in new combinations of alleles

Independent Assortment

In Meiosis 1 homologous pairs of chromosomes line up randomly along the cell equator, so each pair of chromosome lines up, and is separated, independently of all the other pairs

Segregation

In Meiosis 2, chromatids line up randomly along the equator of a cell and are separated. As a result each daughter cell gets one allele for each trait.

Gene

Section of DNA that codes for a particular trait

Allele

Alternative forms of a gene and determine traits. Occur in pairs and are represented by letters. E.g. Tt

Homologous Chromosomes

Chromosomes appear in pairs in which one is inherited from the male parent and the other from the female parent. Each chromosome in a pair is identical in length and shape and contains the same genes, although alleles may be different.

Evolution

Change in allele frequency in a population from one generation to the next

Allele frequencies

The number of a particular allele present in a gene pool

Natural Selection

The process by which individuals who are best suited to their environment survive and pass their genes on to future generations

Directional Selection

Selection towards one extreme of a trait e.g. Giraffe necks

Disruptive Selection

Selection toward both extremes of a trait e.g. Galapagos finches

Stabilising Selection

Selection for intermediate traits e.g. baby birth size

Sexual Selection

Selection by one sex (typically female) for certain characteristics in the other sex e.g. Female peahens choosing male peacocks with the brightest tail feathers

Artificial Selection

Intentional selection on plants and animals by humans for traits the breeder finds desirable.

Genetic Diversity

The range of different alleles within a gene pool. The greater the differences the greater the chances of survival of the species

Gene Pool

Total number of alleles present in population

Adaptation

Traits or characteristics that different organisms develop over time that allow them to be better suited to their environment

Gene Flow

The movement of alleles between populations (influenced by migration of individuals) which can change the frequency of alleles in a population.

Genetic drift

Change in allele frequency due to chance factors. Nothing to do with natural selection

Founder effect

The process by which a small number of individuals leave the original population and colonise a new geographical area. The allele frequency of the founder population is unlikely to be representative of the original population.

Bottleneck effect

When a population size is suddenly reduced in numbers to a small size typically due to a catastrophic event e.g. flood, fire, landslide, habitat destruction, and introduction of predators

Inheritance

Passing genes/alleles from one generation to the next

Genotype

The combination of alleles that code for a particular trait

Phenotype

The visible/observable expression of the genotype

Homozygous Dominant

When an individual carries two dominant alleles for a particular trait

Homozygous Recessive

When an individual carries two recessive alleles for a particular trait

Heterozygous

When an individual carries one dominant and one recessive allele for a particular trait

Trait/Characteristic

A genetically determined quality or feature shown in an individual

F1 Generation

First generation

F2 Generation

Second generation

Dominant allele

Allele that will effectively mask the presence of the other allele. Will be expressed in the phenotype when present.

Recessive allele

Allele will only be expressed in an individual's phenotype when 2 are present, will be masked by the presence of a dominant allele.

Monohybrid inheritance

Inheritance of a characteristic coded for by one gene which has a pair of alleles

Dihybrid inheritance

Inheritance of two characteristics controlled by two genes

Co-dominance

When both alleles are equally dominant, so both will be equally expressed in the heterozygous individual

Incomplete dominance

When neither allele dominates the other and both are present in the heterozygous individual and are expressed as a blend of the two trait

Multiple alleles

When a gene has more than two different alleles resulting in more combinations of alleles therefore resulting in more variation in the phenotype

Lethal alleles

Alleles that produce a non-functional protein and if an affected individual inherits two of the alleles they will either die before birth, shortly after birth or have a greatly reduced life expectancy

Linked genes

When two alleles are located on the same chromosome, therefore are inherited together. Can only be separated by crossing over