Biochemical genetics is a branch of genetics involving the study of genes and their effects on the biochemical pathways. Beadle and Tatum contributed great discoveries in the field of biochemical genetics following the footsteps of Garrod. Beadle and Tatum worked with a haploid fungus known as Neurospora crassa. Since Neurospora spreads like a web, it is known as a mycelial fungus. The asexual spores of Neurospora are known as conidia. This fungus is commonly known as the orange bread mold since the asexual spores or conidia have an orange color. The asexual spores or mycelial pieces get isolated easily for growing them on a suitable medium. Apart from the vegetative or the asexual reproduction, Neurospora also shows the ability to reproduce sexually. This fungus typically shows two mating types. In a nitrogen-limiting medium, these mating types fuse with each other. The fusion of the mating types, later on, initiates other steps such as the fusion of two haploid nuclei forming a diploid nucleus which follows meiosis to produce four haploid nuclei. This step occurs in an elongated sac known as ascus. Each ascus consists of eight ascospores obtained after mitotic division and spore maturation. Beadle and Tatum exploited the above characteristics of Neurospora. They studied auxotrophs and prototrophs in Neurospora. The wild-type strains are known as prototrophs. These strains show their ability to grow on a minimal medium. Based on the chemicals present in the minimal medium, Neurospora synthesized other important functional molecules. Hence, it was possible to isolate mutants that required nutrients to grow (auxotrophs). Beadle and Tatum isolated auxotrophic mutants and induced gene mutations in them using X rays. Then, they crossed them with the wild-type strains. From the resultant crosses, one progeny spore per ascus was allowed to germinate in a nutritionally rich or a complete medium. They also checked whether they grew on a minimal medium. Next round involved the determination of the specific substance needed for an auxotroph to grow on a minimal medium. The strains inoculated in 20 different tubes involved supplementation with one of the 20 different amino acids. In this way, they identified the biochemical pathways. The wild-type strains not only utilized the amino acids for their needs but also converted them into other important compounds involved in various biochemical pathways.