Deoxyribonucleic acid. The material inside the nucleus of cells, carrying the genetic information of a living being.
Organism
Living entity, eg animals, plants or micro-organisms.
Nucleus
The nucleus controls what happens inside the cell. Chromosomes are structures found in the nucleus of most cells.
Chromosome
The structure made of DNA that codes for all the characteristics of an organism.
Gene
The basic unit of genetic material inherited from our parents. A gene is a section of DNA which controls part of a cell's chemistry - particularly protein production.
Allele
Different versions of the same gene.
Genotype
The alleles that an organism has for a particular characteristic, usually written as letters.
Phenotype
The visible characteristics of an organism which occur as a result of its genes.
Dominant allele
An allele that always expresses itself whether it is partnered by a recessive allele or by another like itself.
Recessive allele
Describes the variant of a gene for a particular characteristic which is masked or suppressed in the presence of the dominant variant.
Homozygous
This describes a genotype in which the two alleles for the characteristic are identical.
Heterozygous
This describes a genotype in which the two alleles for a particular characteristic are different.
DNA
Large and complex molecule that carries the genetic code that determines the characteristics of a living organism
Gene
Section of DNA that codes for a specific protein, the unit of heredity
Chromosome
Long threads of DNA, each made up of many genes, found in the nucleus of most cells
James Watson and Francis Crick worked out the structure of DNA in 1953
Double helix
The shape of the DNA molecule, with two strands twisted together in a spiral
Base pairs
Paired chemicals between the two strands of DNA, including thymine, adenine, guanine, and cytosine
Complementary base pairing
Thymine pairs with adenine, guanine pairs with cytosine
Allele
Different forms of a gene, e.g. for eye colour
Triplet code
Sequence of three bases that determines a specific amino acid in a protein
DNA
Hereditary molecule responsible for its function
Genetic cross
Examination and showing of possible offspring combinations using a Punnett square
Carrying out a genetic cross
1. Determine probability of offspring combinations
2. Calculate probability of offspring combinations
Monohybrid cross
Genetic cross of single gene combinations
Punnett square
Shows possible offspring combinations and allows calculation of probability of these combinations
Allele
Alternative form of a gene
Dominant allele
Allele that is expressed when present
Recessive allele
Allele that is only expressed when two copies are present
Genotype
Genetic makeup of an organism
Phenotype
Physical characteristics of an organism
Homozygous
Having two identical alleles for a particular trait
Heterozygous
Having two different alleles for a particular trait
Selfing
Pollen from one flower landing on the stigma of the same flower
Backcross
Cross between an F1 individual and one of its parents
Most phenotypes are controlled by multiple genes
Probability
Extent to which something is likely to be the case
Allele combinations created during fertilisation are a random process
How to construct Punnett squares
1. Determine the parental genotypes
2. Split the alleles for each parental type and add them into your Punnett square around the edges
3. Work out the new possible genetic combinations inside the Punnett square
4. Use this to answer the question
Punnett square
A diagram used to predict the possible genotypes of offspring