This definitions covers Key Definitions within Genetic Inheritance for GCSE Biology. Genetic inheritance patterns, alleles, and inheritance diagrams It is section 4 of 9 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
Topic position
Section 4 of 9
Practice
25 questions
Recall
25 flashcards
Key Definitions
Dominant allele: An allele that is expressed in the phenotype whenever it is present, even if only one copy is inherited. Written with a capital letter (e.g., B).
Recessive allele: An allele that is only expressed in the phenotype when two copies are present (homozygous recessive). Written with a lowercase letter (e.g., b).
Homozygous: Having two identical alleles for a gene (e.g., BB or bb). A homozygous dominant individual (BB) and a homozygous recessive individual (bb) will both breed true for that characteristic.
Heterozygous: Having two different alleles for a gene (e.g., Bb). The dominant allele is expressed in the phenotype, but the recessive allele is still present and can be passed to offspring.
Genotype: The combination of alleles an organism carries for a particular gene (e.g., Bb, BB, or bb). Genotype determines what phenotypes are possible.
Phenotype: The physical or observable characteristic produced by the genotype, e.g., brown eyes (BB or Bb) or blue eyes (bb). Phenotype can also be influenced by environmental factors.
Punnett square: A grid used to predict the possible genotypes and phenotypes of offspring from a genetic cross, based on the gametes produced by each parent.
Carrier: A heterozygous individual (Ff) who carries one recessive allele for a condition but does not show symptoms, because the dominant allele is expressed. Carriers can pass the recessive allele to their children.