What Is Inheritance?
The passing of genetic information (and therefore characteristics) from parents to offspring through reproduction.
Have you ever been told you have your mother's eyes or your father's smile? These resemblances are not a coincidence — they are the result of inheritance. Every characteristic you have, from your blood type to the shape of your earlobes, is influenced by information passed down from your parents in the form of genes.
Understanding how traits are inherited is one of the most powerful ideas in biology. It allows scientists to predict the likelihood of offspring having certain characteristics — and even certain genetic conditions.
Think of your genetic information like a recipe book. Each parent donates half of the recipes, and the combination determines what kind of dish (organism) is produced. Usually one recipe dominates over the other — though in some special cases they interact in more complex ways. For the most part in this unit, we will focus on situations where one allele clearly dominates the other.
Key Genetic Vocabulary
Before we can work with Punnett grids, we need to be comfortable with the essential vocabulary of genetics.
A section of DNA on a chromosome that codes for a specific characteristic, such as eye colour or blood type.
One of two or more alternative versions of a gene. For example, the gene for eye colour has alleles for brown eyes and blue eyes.
An allele whose characteristic is expressed (shown) even when only one copy is present. Written as a capital letter (e.g., B).
An allele whose characteristic is only expressed when two copies are present (i.e., no dominant allele is present). Written as a lowercase letter (e.g., b).
The combination of alleles an organism carries for a particular gene (e.g., BB, Bb, or bb).
The observable characteristic that results from the genotype (e.g., brown eyes or blue eyes).
A quick way to remember the difference: Genotype = Genes (what's written in DNA), Phenotype = Physical appearance (what you can see).
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