Genetic Variation and Change Flashcards
Allele
An alternative form of a gene.
Chiasma
The point at which paired chromosomes contact during crossing over.
Co-dominance
A condition in which an individual who is heterozygous will express the phenotypes associated with both alleles.
Crossing over
A process occurring during meiosis wherein two chromosomes pair up and exchange segments of their genetic material.
Diploid
A cell that contains two complete sets of chromosomes, one from each parent. (In humans somatic cells are diploid as they contain 46 chromosomes.)
Evolution
A gradual process in which something changes into a different and usually more complex or better adapted form.
Founder effect
The reduced genetic diversity that results when a population is descended from a small number of colonising ancestors.
Gamete
A reproductive cell having the haploid number of chromosomes, especially a mature sperm and egg.
Gene
A section of DNA that codes of a particular amino acid.
Gene pool
The total sum of different alleles in an interbreeding population.
Genetic biodiversity
Refers to to the total number of genetic characteristics in the genetic make-up of a species.
Genetic drift
The process of change in the genetic composition of a population due to chance or random events rather than by natural selection.
Genetic variation
Variation in the allele frequency or genome between members of species or between groups of species.
Genotype
The set of alleles that determines the expression of a particular characteristics or trait.
Haploid
A cell that contains a single set of unpaired chromosomes. In humans this means 23 unpaired chromosomes.
Heterozygous
An individual two different alleles for a specific trait.
Homozygous dominant
An organism or cell that contains two dominant alleles for a single trait.
Homozygous recessive
An organism or cell that contains two recessive alleles for a single trait.
Incomplete dominance
A relationship between alleles of a single gene in which one allele masks the phenotypic expression of another allele at the same gene locus.
Independent assortment
The process of random segregation and assortment of chromosomes during meiosis resulting in the production of genetically unique gametes.
Lethal alleles
Alleles that cause an organism to die when present in homozygous condition.
Linked genes
Genes that are inherited together with other gene (s) as they are located close together on the same chromosome.
Locus
The position that a given gene occupies on a chromosomes.
Meiosis
The process of cell division in sexually reproducing organisms that reduces the number of chromosomes in reproductive cells from diploid to haploid.
Multiple alleles
Three or more alleles for a particular gene. The presence of multiple alleles is best illustrated by the ABO blood groups of humans.
Mutagen
An agent, such as a chemical, ultraviolet light or a radioactive element that induce or increase the frequency of mutation in an organism.
Mutation
A permanent change in the base sequence of DNA.
Natural selection
The process whereby organisms better adapted to their environment tend to survive and produce more offspring.
Phenotype
The set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.
Population bottleneck
A sharp reduction in size of a population due to environmental events (such as fires, earthquakes and floods) or human activities.
Pure breeding
When two organisms with identical genotypes produce offspring with the same traits (e.g. both parents are homozygous for a particular trait).
Segregation
The separation of paired alleles or homologous chromosomes, especially during meiosis so that the members of each pair appear in different gametes.
Somatic cells
Any cell of the body that is not a sexually reproductive cell.
Test cross
A cross between an organism whose genotype for a certain trait is unknown and an organism that is homozygous recessive for that trait.
Trait
A genetically determined characteristic or condition.
