Key genetic termsSpec 17.4.1, 17.4.2, 17.4.3, 17.4.4, 17.4.5, 17.4.6, 17.4.7, 17.4.8, 17.4.9
Inheritance is the transmission of genetic information from generation to generation. Parents pass genes to their offspring in their gametes, so offspring have features like their parents.
- Inheritance
- The transmission of genetic information from generation to generation.
- Genotype
- The genetic make-up of an organism and in terms of the alleles present.
- Phenotype
- The observable features of an organism.
- Homozygous
- Having two identical alleles of a particular gene. Example: TT or tt.
- Heterozygous
- Having two different alleles of a particular gene. Example: Tt.
- Dominant allele
- An allele that is expressed if it is present in the genotype.
- Recessive allele
- An allele that is only expressed when there is no dominant allele of the gene present in the genotype.
Dominant alleles are written as capital letters (T) and recessive alleles as lower case letters (t). A heterozygous individual (Tt) shows the dominant feature, because the dominant allele is expressed.
Pure-breeding
Two identical homozygous individuals that breed together will be pure-breeding. For example, TT × TT can only give TT offspring, and tt × tt can only give tt offspring, so every generation looks the same.
A heterozygous individual will not be pure-breeding. A Tt parent makes two types of gamete (T and t), so its offspring can have different genotypes and different phenotypes.
Genotype is the alleles, such as Tt. Phenotype is what you can see, such as tall. Do not swap them, and do not say a recessive allele is 'weaker'.
Heterozygous and homozygous describe genotypes only. Do not use them for phenotypes.