Back in the day, Mendel crossed different varieties of pea plants to establish rules of inheritance. He didn’t know what we know today about genes and DNA. So what do we know, and what did he find out?
The entirety of genetic material in an organism is called a genotype. It can also refer to specific things, like a genotype for a certain trait in a given organism.
The genotype refers to the physical constitution of a little part of DNA. Its expression, however (that is what protein a gene encodes, and what that protein ends up doing in the organism) is a separate entity which is subject to environmental influence. This is called the phenotype.
Humans have 2 sets of chromosomes, so for each distinct chromosome e.g. chromosome 1, there are two copies. How do the same genes on both homologous chromosomes interact if they result in different phenotypes? Which has priority…