Inbreeding at One Locus - Selfing - Heterozygosity through the Generations

AA and aa are the genotyhpes of two inbred lines differing at a locus. They are crossed to produce an F1 which is composed of individuals with genotype Aa. This is shown as the first Parental Generation in the histogram box. Each of these 100 parents is removed from the Parental Generation and selfed, producing exactly one offspring which is added to the Offspring Generation histogram. After all the parents are selfed, the resulting generation of 100 offspring is seen, and it can be "promoted" to be the parents of the next selfed generation. In plant breeding this is referred to as "single seed descent". A record is kept of each generation in the box at the bottom. The first offspring group produced will be called the first (selfed) generation and succeeding generations will be numbered from that point.

You can test your understanding of this random process by predicting the number of Aa individuals expected for the Offspring Generation before clicking on "Run." Type a numerical value into the indicated box. After the Run, a comment or two will appear in the text box below the Run button.

This exercise emphasizes the pattern of decreasing heterozygosity during the process of inbreeding. A different exercise illustrates the genetics of producing selfed offspring. Work through it to follow the production of gametes and offspring and to see the Thought Questions covering the entire process of inbreeding.

Parental Generation

AA       Aa           aa
Offspring Generation

AA         Aa         aa
Before you start inbreeding this generation - think about the process and type in your numerical prediction of how many Aa individuals will be in the Offspring Generation (Note: the parental generation counts are in the box down below):

To get ready to Run the Next Generation:

To start all over again click: and then proceed as before.

Thought Questions

Please send comments to   --henry schaffer

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Copyright © 2000, 2017, 2018 by Henry E. Schaffer   Last modified 9/3/2018