Final answer:
The biochemical units of heredity that make up chromosomes are called genes. They are sequences of DNA that encode for specific proteins, crucial for the functions of the cell. The traits of an organism are determined by the specific combination of inherited genes.
Step-by-step explanation:
The biochemical units of heredity that make up the chromosomes are known as genes. They serve as the physical and functional units of heredity; a sequence of DNA that codes for a specific peptide or RNA molecule. When considering the options provided, the correct choice is 'a. genes.' Genes are linearly arranged on chromosomes and specify the sequences of amino acids, which are the building blocks of proteins. These proteins are responsible for orchestrating nearly every function of the cell.
About the other options, a genome refers to the entire genetic complement (DNA) of an organism. Molecular genetics is a branch of biology that focusses on the structure and function of genes at a molecular level. Neurotransmitters are chemical messengers in the body, not related to genetic heredity. And finally, heredity is the overall process through which traits are passed from parents to offspring, but not a unit of chromosomes.
Regarding the second question, an organism's traits are determined by the specific combination of inherited genes. Traits are the variations of characteristics that are expressed. The genotype, which consists of an organism's genes, expresses the phenotype or observable traits through the sequencing of DNA. Changes in the sequence create alleles, which then determine specific traits.