IB Biology D3.2 Notes

Topic D3.2 focuses on inheritance of genes by offspring. Genes are defined as a heritable factor consisting of a length of DNA that influences a specific characteristic. Such an example of a characteristic is hair.

Different versions of this gene are called alleles, which each code for a different version of that characteristics. An example would be that three alleles would code for blonde, brown, or black hair, respectively. However, only one allele can occupy a position on a chromosome, called a locus.

Loci have a specific notation:

1. This starts with the number of the chromosome.
2. Then, p stands for short arm and q stands for the long arm. 
3. Lastly, the position of the gene is listed. 

For example, the human gene for the hemoglobin β-polypeptide is gene 15.4 on the short arm of chromosome 11. Its notation is thus 11p15.4.