Difference Between Genes & Alleles

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  • 0:00 DNA and Heredity
  • 0:51 Genes and Alleles
  • 1:57 Gene Expression
  • 4:18 Lesson Summary
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Lesson Transcript
Instructor: Bridgett Payseur

Bridgett has a PhD in microbiology and immunology and teaches college biology.

Genes are passed from parent to child. Each parent provides one variation of the gene, called an allele, to the child. This lesson will discuss how genetic information is inherited and how it is expressed.

DNA and Heredity

You may have heard DNA called 'the building blocks of life'. How did DNA earn this title? DNA is the information in your cells that is passed from one generation to the next. It contains all the instructions your cells need to do everything they do - including building you. The instructions contained in DNA tell your cells how to make proteins. Proteins are the workers of the cell; they do everything. Proteins provide structure, such as in your hair and nails, they make your muscles move, they even help chemical reactions happen.

DNA is passed on from cell to cell and from parent to child. The traits passed down via DNA from generation to generation are called heritable, meaning they can be inherited by the offspring. Heredity describes how these traits are passed on.

Genes and Alleles

The information contained in DNA is arranged in genes. A gene provides the directions to make one specific protein. This can be the protein that makes your eyes brown, digests a specific sugar, or makes your fingernails. Genes are found on structures called chromosomes, long pieces of DNA wound up around protein. Each chromosome contains many, many genes. And a specific gene, such as the gene for eye color, is at the same location on the same chromosome in every person.

Your cells have two sets of chromosomes, called homologous pairs. These chromosomes have the same genes, but might have different versions of those genes. The different possible versions of the genes are called alleles. For example, one homologous chromosome may have the allele for blue eyes, while the other has the allele for brown eyes.

Why do you have two sets of chromosomes in each cell? The answer is: it's all your parents' fault. You inherit one set of chromosomes from each parent. This is how they can each pass on some information to you.

Gene Expression

Considering that you have over 20,000 genes, it is highly unlikely that each of your parents will give you the same allele for each gene. If the alleles match up at a certain gene, it is called being homozygous (homo means same, zygote means fertilized egg). If the alleles don't match up, it is called heterozygous (hetero means different).

If a certain gene is homozygous, meaning both alleles are the same, it is easy to determine what will be expressed. There is only one option. For example, if the gene for blue eyes has two blue eye alleles, the person will obviously have blue eyes. There is no other possible allele that could be expressed.

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