Heredity: Also known as INHERITANCE is the transmission and expression of characters or traits in organisms from parents to their offspring.
Variation: This is the differences which exist between parents and offspring as well as among the offspring. I.e. Even though offspring may resemble their parents, they can also from them in one way or the other.
Heredity Variation :
This refers to differences among individuals which can be passed from parents to their offspring (progeny). This arises because, apart from cases of identical twins, no two offspring inherit exactly the same set of characteristics from their parents.
Transmittable Characters in Human Beings:
Only characters controlled by genes can be transmitted. I.e, inherited characters are determined by genes. A diploid Organism has two sets of chromosomes referred to as homologues. Such an Organism has two copies of each gene, with the copies occupying identical locations or loci on the homologous chromosomes.
Image Source: http://learn.genetics.utah.edu/content/pigeons/sexlinkage
Genes : They are hereditary units or basic units of inheritance which are located in chromosomes and are responsible for the transmission of characters from parents to offsprings.
Chromosomes: They are rod or thread-like bodies found in the nucleus of a cell. It contains the genes.
Gamete: This are matured sex cell which takes part in sexual reproduction. There are two types: male gamete (in animals) and pollen grains (in plants) while is called the female gamete, egg (in animals) and ovules (in plants).
Zygote: Is a single cell formed as a result of the union of a male gamete with a female gamete.
Phenotype: Is the sum total of all observable features of an Organism, I.e; physical, behavioural and physiological traits e.g height, skin colour, weight e.t.c.
Allelomorphs: This are pairs of genes on the position of a chromosomes that control contrasting characters.
Genotype: This is used to describe those traits or sum total of the genes inherited from both parents. It includes both the dominant and the recessive traits that form the genetic make-up of an individual.
Dominant character: This is trait or character that is expressed in an offspring when two individuals with contrasting characters or traits are crossed. Dominant genes are genes which control dominant characters.
Recessive character: This is the character or traits from one parent which is masked or does not produce the effect in the presence of dominant character. ** Recessive genes** are genes which control recessive characters.
Homozygous: An individual is said to be homozygous if it has two similar genes for the same character I.e. the pair of genes controlling a given pair of contrasting characteristics are identical e.g (TT) for tallness or (tt) for shortness.
Heterozygous: An individual is said to be heterozygous if the two members of a pair of genes controlling a pair of contrasting characters are different.
Hybrid: This are offspring from a cross between parents that are genetically different but of the same species.
Hybridization: This is the crossing of plants with contrasting characters.
Monohybridization involves the crossing of two pure traits while Dihybridization involves the crossing of plants with two pairs of contrasting characters.
Haploid: This is when an Organism has one set of chromosomes in a gamete.
Locus: This is the site for location of a gene in chromosome.
Mutation: This is a change in the genetic make-up of an Organism resulting in a new characteristics that is inheritable.
Diploid: Diploid is when an Organism has two sets of chromosomes in the body cell.
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