What is Hereditary Patterns?
We’ve all heard that we get certain traits from our parents, such as eye color or height. These traits are passed on through the genes in our DNA. Half of our DNA comes from our mother and the other half from our father.
Scientists have discovered that genes are inherited according to certain patterns. The genes of your parents and grandparents affect your genes. On this page, we will learn how these models work.
We learned some inheritance basics on Mendel and Inheritance. You can also check out our DNA and Chromosomes page to learn more.
Below we have provided a few points you should know about genes and inheritance:
Gene – Inside the DNA molecule there are pieces of information called genes. Each gene tells the cell how to make a certain protein that can determine a trait such as eye color.
Allele – While a part of DNA is called a gene, a specific pattern in a gene is called an allele. For example, genes determine hair color. The specific phenotype of the gene that determines the hair color that makes the hair black will be the allele.
Dominant and Recessive Genes
Each child inherits two genes for each trait from their parents. Some genes are dominant over others. For example, brown eyes are dominant over blue eyes. If someone has the brown-eyed gene and the blue-eyed gene, they will have brown eyes. They will only have blue eyes if both genes are blue.
The gene for brown eyes is called the dominant gene and the gene for blue eyes is recessive.
Writing out the Genes
To write the specific allele that a person has for a gene, you write one letter for the mother’s gene and one letter for the father’s gene. The dominant gene is capitalized, the recessive gene is lowercase. Here is an example:
We use a capital letter “B” to indicate the dominant brown-eyed gene and a lowercase “b” to indicate the recessive blue-eyed gene.
- Bb – 1 brown gene, 1 blue gene (person will brown eyes)
- BB – both brown genes (person have brown eyes)
- bb – both blue genes (person have blue eyes)
The main way to determine the type of inheritance that can come from two parents is to use a Punnet square. A Punnet square shows all possible combinations of the parent genes.
We will take the example of a plant that can have purple or white flowers. The purple gene is dominant and is written as “P”. The white gene is recessive, so we write it as “w”. Here is an example of a Punnet square where one parent has two purple “P” genes and the other father has two white “w” genes.
Each child has the same “Pw” genetic profile. They both carry the P dominant gene and both have purple flowers.
Here’s another example where each parent has one purple gene and one white gene (Pw):
In this case, you can see that 75% of the children will have a dominant “P” gene and will have a purple flower. However, 25% of children with the “ww” gene will have white flowers.
More Punnet Square Examples
In this example, one parent is PP and the other Pw.
All offspring will have purple flowers, but since either parent carries the recessive “w” gene, 50% of the offspring will pass on the “w” gene.
Now let’s see what happens if only one parent has a dominant gene P where one is “Pw” and the other is “ww”.
You can see that 50% of the children will have white flowers and 50% purple.
Interesting Facts about Hereditary Patterns
The set of genes of an individual is called the genotype.
The physical appearance produced by the alleles (e.g. actual purple flowers) is called the phenotype.
If two genes are the same (eg ww or PP) it is said to be homozygous.
If the two genes are different (eg Pw) then it is said to be heterozygous.
Sometimes genes are “co-dominant,” meaning that no gene is dominant over the other. An example of this is blood type where one parent has blood type A and the other has blood type B. The child will have blood type AB.
Some traits are determined by more than one gene.