Genetic Inheritance

Genetics is the study of inheritance, the passing of traits from one generation to the next. Cell continuity relies on inheritance.

Fertilisation

• To produce a new individual, gametes must fuse during fertilisation.

Alleles and Genes

• Allele: A different form of the same gene.
  • Example: Brown and blue eye colour are different alleles of the same gene.
  • Alleles are found at the same position (locus) on homologous chromosomes.
• Locus: The position of a gene on a chromosome.
  • If the two alleles are the same, they are called homozygous.
  • If the two alleles are different, they are called heterozygous.

Dominant and Recessive Alleles

• Let's use B as the symbol for the allele for brown eyes and b for blue eyes.
• Genotype: The genetic make-up of an organism (e.g., BB, Bb, or bb).
• Phenotype: The physical appearance or trait expressed by the organism (e.g., brown eyes or blue eyes).

1. Homozygous Dominant (BB):

• Genotype: BB (both alleles are dominant).
• Phenotype: Brown eyes (dominant trait is expressed).

2. Homozygous Recessive (bb):

• Genotype: bb (both alleles are recessive).
• Phenotype: Blue eyes (recessive trait is expressed).

3. Heterozygous (Bb):

• Genotype: Bb (one dominant allele and one recessive allele).
• Phenotype: Brown eyes (dominant allele B masks the recessive allele b).

Representation of Alleles

• A capital letter is used for the dominant allele, and the corresponding lowercase letter represents the recessive allele.
• Example: If purple flowers are dominant over white flowers in a plant, P represents purple, and p represents white.