Gregor Mendel is named the "Father of Genetics" because he was the first to began to perform experimentation on genetics and heredity by crossing pea plant genes after he noticed variation between pea plant flower colors.
In Mendel's studies two alleles combined to create one single gene. Alleles are represented using one single letter, and a gene is represented by a pair of the same letter. Each gene or allele can either be dominant (capital letter) or recessive (lowercase letter).
A homozygous gene is when two of the same type of alleles combine together while heterozygous genes is when there is a dominant and recessive gene combined. All of these things is what makes up an organisms genotype.
A organisms phenotype is what we can see physically expressed, such as eye color and height. Recessive traits can also be present in an organism, for example if a mother had a dominant trait for brown eyes and a recessive trait for blue eyes and a father had a recessive trait for blue eyes, their offspring could possibly have blue eyes. This is known as Mendel's Principle of Dominance.
Variations in your height, hair, skin and eye color are all controlled by an epigenome which is an outer layer of genetic information around DNA, which allows for the expression of traits.
There are two different ways in which crossbreeding organisms is done to make sure their offspring get specific desired traits. One way is a monohybrid cross which is a crossbreed done to pass on one desired trait to offspring. The other way is the dihybrid cross which is a crossbreed done to pass on two of the desired traits.
The punnet-square is a tool that is used to determine the probabilities of the genotypes and phenotypes that will be passed on to the offspring. The punnet squares depending on the organism has 2-4 different outcomes decided by how the dominant and recessive genes combine.
Incomplete dominance occurs when there is a blending of traits due to the presence of multiple dominant genes. Such as a mixed child. With codominance both alleles contribute equally to the phenotype, resulting in a sharply contrasting appearance in color/variation, etc. through the organism such as albinism.
Humans have 23 chromosomes. Chromosomes 1-22 are autosomes. Chromosome 23 are the sex chromosomes which determine whether or not you are male or female depending on whether you have XX chromosomes or XY chromosomes. Traits that are passed through the 23 chromosome are considered sex linked traits.
When an organism doesn't display a genetic disease but has an allele for it that can be passed down, these organisms are known as carriers . A pedigree is a tool that can be used to track certain traits through generations.