3.7.1 Inheritance

• Genotype is the genetic constitution of an organism.
• Phenotype is the expression of this genetic constitution and its interaction with the environment.
• Allele is an alternative form of a gene.
• If both alleles are the same on the homologues, the organism is homozygous for that characteristic.
• If the alleles are different, the organism is heterozygous for the characteristic.
• Alleles may be dominant, recessive or codominant.
• Dominant is the allele of the heterozygote that is expressed in the phenotype.
• Recessive is the allele of the heterozygote that is not expressed.
• Codominant means both alleles contribute to the phenotype.
• Monohybrid inheritance is the inheritance of a single gene.
• Pure-breeding is repeated breeding of organisms for a particular characteristic.
• In monohybrid inheritance, the organism will be homozygous for this gene if it is pure-bred.
• If one pure-bred organism is crossed with another, all the offsprings will be heterozygous for this gene in monohybrid inheritance.
• The pure-bred are the parental (P) generation while the heterozygous offsprings are called F1 (first filial) in monohybrid inheritance.
• In diploid organisms, characteristics are determined by alleles that occur in pairs.
• Only one of each pair of alleles can be present in a single gamete in diploid organisms.