Biology for Kids
We all have heard how we get certain traits from our parents such as the color of our eyes or how tall we are. These traits are passed on by genes in our DNA. Half of our DNA comes from our mother and half from our father.
Scientists have discovered that genes are inherited in certain patterns. What genes your parents and grandparents have, affects what genes you have. On this page we will learn how those patterns work.
We learned some of the basics about inheritance on the Mendel and Inheritance page. You can also go to our DNA page and our chromosome page to learn more.
A few things you should know about genes and inheritance:
Gene - Inside the DNA molecule are sections of information called genes. Each gene tells the cell how to make a certain protein which may determine a trait such as the color of the eyes.
Allele - While the section of DNA is called a gene, a specific pattern in a gene is called an allele. For example, the gene would determine the hair color. The specific pattern of the hair color gene that causes the hair to be black would be the allele.
Dominant and Recessive Genes
Each child inherits two genes for each trait from their parents. Some genes are more dominant than others. For example, brown eyes are dominant over blue eyes. If someone has a brown eyed gene and a blue eye gene, they will have brown eyes. They will only have blue eyes if both genes are blue.
The brown eyed gene is called the dominant gene and the blue eyed gene is the recessive gene.
Writing out the Genes
In order to write out the specific allele a person has for a gene, you write a letter representing the gene from the mother and a letter for the gene from the father. Dominant genes are written with capital letters and recessive genes with lower case letters. Here is an example:
We use the capital letter "B" to represent the dominant brown-eyed gene and a lower case "b" to represent the recessive blue-eyed gene.
- Bb - one brown gene, one blue gene (this person will have brown eyes)
- BB - both brown genes (this person will have brown eyes)
- bb - both blue genes (this person will have blue eyes)
The main way to figure out the pattern of inheritance that could come from two parents is using a Punnet square. A Punnet square shows all the possible combinations of genes from the parents.
We will use the example of a plant that could have a purple flower or a white flower. The purple gene is dominant and we write it "P." The white gene is recessive, so we write it "w." Here is an example of a Punnet square where one parent has two purple genes "P" and the other parent has two white "w" genes.
Each child has the same gene pattern "Pw". They all have the dominant P gene and will all have purple flowers.
Here is another example where each parent has a purple gene and a 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 the children have "ww" genes and will have a white flower.
More Punnet Square Examples
In this example, one parent is PP and the other Pw.
All of the children will have purple flowers, but because one parent has a recessive "w" gene, 50% of the children will pass on the "w" gene.
Now look at what happens if only one parent has a single dominant P gene where one parent is "Pw" and the other "ww".
You can see that 50% of the children will have white flowers and 50% purple.
Interesting Facts about Hereditary Patterns
- All of an individual's genes together are called the genotype.
- The physical appearance that results from the alleles (for example, the actual purple flower) is called the phenotype.
- If the two genes are the same (for example, ww or PP), this is called homozygous.
- If the two genes are different (for example Pw), this is called heterozygous.
- Sometimes gene types have "codominance" meaning that neither gene is dominant over the other. One example of this is blood type where one parent has type A and the other has type B. The child will have blood type AB.
- Some traits are determined by multiple genes.
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