Single Gene Inheritance
- Some characteristics are controlled by a single gene, this is called monohybrid inheritance (mono = one)
- As we have two copies of each chromosome, we have two copies of each gene and therefore two alleles for each gene
- One of the alleles is inherited from the mother and the other from the father
- This means it is possible to have two different alleles for a gene
- For example, two copies of a particular gene could contribute to eye colour but one allele could code for brown eyes and one allele could code for blue eyes
- The observable characteristics of an organism is called the phenotype
- For example: eye colour or blood type
- The combination of alleles that control each characteristic is called the genotype and is usually represented using letters
- For example: Bb might be a genotype for brown eyes
Allele types
- Alleles can be
- Dominant: it only needs to be inherited from one parent in order for the characteristic to show up in the phenotype
- Recessive: It needs to be inherited from both parents (have 2 copies of in the genotype) in order for the characteristic to show up in the phenotype.
- If there is only one recessive allele, it will remain hidden and the dominant characteristic will show
- If the two alleles of a gene are the same, we describe the individual as being homozygous (homo = same)
- An individual could be homozygous dominant (having two copies of the dominant allele), or homozygous recessive (having two copies of the recessive allele)
- If the two alleles of a gene are different, we describe the individual as being heterozygous (hetero = different)
- When completing genetic diagrams, alleles are abbreviated to single letters
- The dominant allele is given a capital letter
- The recessive allele is given the same letter, but lower case
Alleles can be dominant or recessive