Studied by 8 people
Allele
Different versions of a gene.
Asexual reproduction
Reproduction involving only one parent - producing identical offspring.
Bases
Adenine
Carrier
Has inherited a genetic trait or mutation
Characteristic
An attribute of an individual
Chromosome
Strand of DNA which contains many genes; a normal human cell has 46 (23 pairs).
Complementary base pairing
Used to describe how the bases bond
Continuous variation
Variation that shows a range/gradual change
Diploid
A cell with the full complement of chromosomes (46 in humans).
Discontinuous variation
Variation that is either/or e.g. blood groups
DNA
The chemical which carries genetic information in the nuclei of cells. Made up of phosphate units
Dominant
The allele which will be expressed in the phenotype if it is present. Shown as an uppercase letter.
Double Helix
Name given to the twisted ladder shape of DNA.
Fertilisation
When a male sex cell (gamete) combines with a female sex cell (gamete) to form a zygote.
Gamete
A sex cell e.g. egg or sperm in animals
Genetic variation
The differences among parents and their offspring or among individuals in a population.
Genotype
Piece of DNA which codes for a particular protein and therefore a characteristic
Haploid
Cell with half the complement of chromosomes (23 in humans).
Heterozygous
Having a dominant and a recessive allele
Homozygous
A pair of alleles that are the same
Hydrogen bonds
Attractive forces that hold the two strands of DNA together.
Inheritable
The information can be passed on to the offspring.
Karyotype
A photograph or diagram of the chromosomes of the cell arranged in an orderly fashion.
Meiosis
Cell division that reduces the number of chromosomes to half the normal number
Mitosis
Cell division that maintains the normal number of chromosomes
Monohybrid cross
A straightforward cross involving only one pair of genes or alleles.
Natural selection
Organisms with characteristics best suited to their environment become more successful
Mutation
A sudden
Non-inheritable
Information that cannot be passed on to the offspring as it is due to a change in the somatic cells or due to the environment.
Nucleotide
A unit built up of a base
Pedigree chart
A family tree drawn with standard genetic symbols
Phenotype ratio
Ratio of phenotypes e.g. 3 brown hair : 1 blonde hair (a prediction of the phenotypes and their occurrence as a result of a cross).
Phenotype
The expression of the genotype. The physical appearance of a trait.
Phosphate
Group that alternates with the ribose sugar in the DNA backbone.
Punnett square
Name given to the grid of squares that may be drawn to show the possible combinations of alleles in a genetic cross.
Pure breeding
A group of identical individuals that always produce offspring of the same phenotype when interbred. They are homozygous for a trait
Recessive
The allele which is only expressed in a phenotype if there are 2 of them present
Ribose
Sugar group that alternates with the phosphate group on the DNA backbone.
Semi conservative
Each double-stranded DNA molecule is composed of one parental strand
Sexual reproduction
Reproduction involving 2 parents
Somatic
Body cells.
Trait
Another word for characteristic
Triplet code
Variation
Differences in DNA/alleles/genes. Differences within a species.
Zygote
Cell formed when a sperm cell fuses with an egg cell.
The Bottleneck Effect
A reduction in the genetic diversity of a population caused by a reduction in its size due to a disaster.
Founder effect
When a small number of individuals colonize a new area; the new gene pool is not reflective of original population.
Gene flow
Movement of alleles into or out of a population due to the migration of individuals to or from the population
Immigration
Where individuals more into a population
Population
A group of individuals of the same species that live in the same area.
Crossing over
The exchange of genes between homologous chromosomes
Species
A group of similar organisms that can breed and produce fertile offspring.
Chiasma
The site of crossing over.
Recombination
The genetic process by which one chromosome breaks off and attaches to another chromosome during reproductive cell division.
Directional selection
Occurs when natural selection favors one of the extreme variations of a trait.
Stabilising selection
Selection for the middle range against the extremes.
Centromere
Region of a chromosome where the two sister chromatids attach.
Segregation
Separation of alleles during gamete formation.
Adaptation
Characteristic that increases an organism's chance of survival.
Evolution
The gradual change in a species over time.
Gene pool
Combined genetic information of all the members of a particular population.
Genetic drift
A change in the allele frequency of a population as a result of chance events rather than natural selection.
Genetic equilibrium
situation in which allele frequencies in a population remain the same.
Mate selection
The process by which individuals choose each other for mating.
Speciation
The formation of new and distinct species in the course of evolution.
Selective pressure
When the environment pushes an individual or population to adapt or evolve.
Locus
Location of a gene on a chromosome.
Disruptive selection
Favors individuals at both extremes of the phenotypic range.
Allele frequency
How often a form of a gene appears in a gene pool.
Independent assortment
The random distribution of the pairs of genes from different chromosomes to the gametes.
