Genetics is the branch of biology that studies heredity and how genes are passed on from generation to generation. Gregor Mendel is accredited with being the “Father of Genetics” because he was one of the first scientists to study the inheritance of traits.
Genes are segments of DNA. DNA stands for deoxyribose nucleic acid. DNA is made of smaller building blocks called nucleotides. Each nucleotide consists of a deoxyribose sugar, a phosphate group, and a nitrogen base. There are four kinds of nitrogen bases in DNA. DNA’s nitrogen bases are adenine, thymine, cytosine, and guanine. The order of the nucleotides determines the gene that an individual will have.
Most human genes are made of at least two alleles. Alleles are possible forms or varieties of a gene. In basic genetics, individuals receive on allele from each parent for each trait. Alleles can be dominant or recessive. Dominant genes are the “stronger” variety of the gene, while recessive alleles are considered to be “weaker." Dominant alleles are represented with a capital letter. Recessive alleles are represented with lowercase letters.
Genotypes refer to the allele combinations that an individual contains. Phenotypes are the physical characteristics represented by genotypes.
Genotypes can be homozygous dominant, heterozygous, or homozygous recessive. If homozygous dominant, an individual has a genotype with two dominant alleles and will show the dominant phenotype. If heterozygous, an individual has one dominant and one recessive allele. Because a dominant allele is present, the individual will show the dominant phenotype. Homozygous recessive genotypes contain two recessive alleles. This is the only way that an individual can manifest the recessive phenotype when dealing with basic genetics.