Biology: Genetic Variation

Mutation

A permanent change in the DNA sequence which creates new alleles, leading to variation in traits. These alleles can be inherited if the mutation occurs in the gametes.

Migration/Gene Flow

The transfer of genetic material from one population to another due to the movement of individuals, increasing genetic variation.

Bottleneck Effect

When the population of a species experiences a sharp decrease due to either natural disaster or human interference. Often there is a loss of genetic variation meaning that the new population is not representative of the original population.

Founder Effect

Occurs when a new population is started by small group of individuals from a larger parent population. The genetic variation is decreased, and non-representative of the original population.

Genetic Drift

The change in allele frequency in a population due to random chance.

Natural Selection

The process where organisms which are best adapted to their environment survive to adulthood and reproduce - those with favorable alleles are selected for and those with unfavorable alleles are selected against.

Allele Frequency

The proportion of individuals in a population with a particular allele.

Lethal alleles

Alleles that cause the death of the organism carrying them

Gene pool

All the genes or alleles present within a population

Co-dominance

Occurs in heterozygous individuals where both alleles are fully expressed in the phenotype.

Incomplete dominance

Occurs in heterozygous individuals where neither allele is completely dominate, resulting in a intermediate phenotype that is a blend of two traits.

Complete dominance

Occurs in heterozygous individuals where the dominant allele is always expressed which masks the effect of the recessive allele.

Multiple alleles

Where there are more than two alleles for a gene within a population (eg. Blood types)

Linked Genes

Genes located closely together on the same chromosome, leading to them being inherited together as they cannot separate independently.

Unlinked Genes

Genes located on different chromosomes or far apart on the same chromosome.

Sex Linked Genes

Traits or characteristics influenced by genes located on the sex chromosomes.

Parental type

Offspring that have the same phenotypic traits as one of the original parents.

Recombinants

Offspring that are a combination/blend/mixture of traits from both parents due to crossing over.

Stabilising Selection

Natural selection that favors the intermediate variants by acting against extreme phenotypes.

Disruptive Selection

Natural selection that favors individuals at both extreme ends rather than intermediate traits.

Directional Selection

Natural selection that favors individuals at one extreme, shifting allele frequencies in a single direction.

Crossing over

The exchange of genetic material between non-sister chromatids of homologous chromosomes during meiosis, creating new combinations of alleles.

Segregation

The process during meiosis where allele pairs separate so that each gamete carries only one allele for each gene.

Independant assortment

The random alignment and separation of homologous pairs during meiosis, resulting in gametes with unique combinations of maternal and paternal chromosomes.

Chromatids

One of the two identical strands of a replicated chromosome that are produced during cell division. Each chromatid becomes a new chromosome in the cells produced during cell division.