Genetics Basic Concepts
Heredity refers to the genetic heritage passed down by our biological parents. It’s why we look like them! More specifically, it is the transmission of traits from one generation to the next. These traits can be physical, such as eye colour, blood type or a disease, or behavioural. For example, the “hygienic” behaviour of honeybees that drives them to remove sick larvae from the nest is inherited behaviour.
Hereditary traits are determined by genes, and a single gene can have several variants called “alleles.” There are two copies of each gene in our cells (with the exception of genes located on sex chromosomes). One of the copies comes from the sperm, the other from the egg. In an individual, these two copies (or alleles) are not necessarily identical. If the two copies of a gene are identical, we say that the individual is homozygous for that gene. If the two copies are different, the gene is heterozygous.
The alleles of the same gene can have a dominant or recessive relationship with one another. If both alleles are different (heterozygous) and at least one of these two alleles is dominant, it is the dominant one that will be expressed (i.e., that we will observe as a trait in an individual). Conversely, a recessive allele (non-dominant) will not be expressed in an individual if both parents pass down the same allele (homozygote). As a result, even if a recessive allele is present in a genotype (the genetic constitution of an individual), it will not be observable in the phenotype (the set of observable traits of an individual) if the other copy of the gene is a dominant allele.
During reproduction, the genes of biological parents combine to form a new unique individual. This shuffling of genes is the reason all of us are different!
Gregor Mendel, a monk and botanist, conducted experiments in the 19th century. He experimented on different characteristics of garden pea plants which always presented two alleles: white or purple flowers, yellow or green peas, etc. He discovered the laws by which genes are passed on from one generation to the other. These are known as “Mendel’s laws.”