# 126 Inheritance - key definitions

Inheritance is the transmission of genetic information from one generation to the next, leading to continuity of the species and variation within it.

Key definitions 

Chromosome	A thread of DNA, made up of genes.
Allele	An alternative form of a gene. Pairs of alleles occupy the same relative positions on chromosome pairs.
Gene	A section of DNA, which codes for the formation of a protein controlling a specific characteristic of the organism.
Haploid nucleus	A nucleus containing a single set of unpaired chromosomes, e.g. in sperm and ova (eggs). In humans, the haploid number is 23.
Diploid nucleus	A nucleus containing pairs of chromosomes, e.g. in somatic (body) cells, In humans the diploid number is 46.
Genotype	The genetic make-up of an organism, e.g. Tt, where T and t are alleles of a gene.
Phenotype	The characteristics visible in an organism, controlled by the genotype, e.g. a tall plant or a dwarf plant.
Homozygous	Having a pair of identical alleles controlling the same characteristics, e.g. TT, where T=tall. The organism will be pure-breeding for that characteristics.
Heterozygous	Having a pair of dissimilar alleles for a characteristic, e.g. Tt.
Dominant	A gene, e.g. T, that always shows in the phenotype of an organism whether the organism is heterozygous (Tt) or homozygous (TT).
Recessive	A gene, e.g. t, that only has an effect on the phenotype when the organism is homozygous (tt)

Video: The Human Genome Project, 3D Animation