Variation and Inheritance

Discrete variation Continuous variation

Blood groups Earlobes attachment Tongue rolling Fingerprint shape - a characteristic shows discrete variation if it can be used to divide the species into two or more distinct groups

Weight Birth weight Skin colour - a characteristic shows continuous variation if members of the species vary in a smooth continuous manner over a range of values- there are no distinct groups

Continuous variation traits are controlled by many genes this is shown by polygenic inheritance

Single gene

The physical appearance of an organism

The genes (alleles) that an organism possesses. Usually written as letters e.g. BB

Different forms of the same gene

An allele that always expresses itself whether it is partnered by a recessive allele or by another like itself

An allele that will only be expressed in the phenotype if it is paired with another recessive allele

This describes a genotype in which the two alleles for the characteristics are identical e.g. BB or bb

This describes a genotype in which two alleles for a particular characteristics are different e.g. Bb

An organism possessing two identical alleles for a particular trait i.e. They are homozygous for a trait