Heredity is the transfer of characteristics from parent to offspring through genes. A gene, the “unit of heredity,” is made of deoxyribonucleic acid (DNA). There are many genes on each molecule of DNA.
Genotypes & Phenotypes
The genotype is an organism’s genetic makeup. For example, all of your genes are what comprise your genotype. The expression of those genes is called your phenotype, your traits that result when the instructions in your genes are carried out.
Alleles
Alleles are variations of a gene. We get one set of alleles (genes) from one parent and the other set of alleles from the other parent.
Some of the traits that we have are based on simple inheritance where one version of a gene (dominant allele) masks the expression of the other version of that gene (recessive allele).
In writing, we represented dominant and recessive alleles with letters that distinguish the different types of alleles. A capital letter is used to represent the dominant allele and a lower-case letter is used to represent the recessive allele (example: dominant allele = P; recessive allele = p)
Homozygous and Heterozygous
When an organism has a pair of identical alleles for a character, they are said to be homozygous for that characteristic (PP, pp); the other option, two different alleles for a gene (Pp). This would represent the heterozygous condition for a characteristic.
Quick Links to Articles on Specific Inheritance Patterns
Complete Genetic Dominance: Examples of Simple Inheritance: Melanin (Eye Color) & Myopia
Learn about genetic traits by examining some of your own! This article explores the genetic of iris pigment and nearsightedness.
Simple Genetic Inheritance: Complete Dominance: Facial Dimples, Chin Cleft & Free Earlobes
Understand heredity first hand by examining actual examples of dominant phenotypes. The dominant trait is not always the most common!
Dominant Human Genetic Traits: Complete Dominance of Mid-digital Hair, Hand Clasping & Bent Finger
It's much easier to understand genetics and heredity if you examine actual examples of dominant and recessive phenotypes that you possess.
Genotype, Phenotype & Heredity: The Inheritance of Homozygous and Heterozygous Characteristics
What is the relationship between genes, chromosomes and DNA? Genotypes, phenotypes and alleles? Read on to learn how inheritance works.
More Genetics Resources
See the science education website Science Prof Online for more information of genetic inheritance patterns or look to other Genetics & Evolution Suite 101 articles.
Sources
Thorpe ed. (2007) Biology 120 Lab Manual. Grand Valley State University.
Doezema, B. (2006) Biology 101 Lab Manual. Grand Rapids Community College.
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