Inbreeding at One Locus - Selfing

Also known as "single seed descent."

Starting with AA and aa, two inbred lines differing at a locus, an F1 is produced. It 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 selfed, producing exactly one offspring, under the controls of the buttons below. The combination of two random gametes from from the single selfed parent produce the genotype. After all the parents are selfed, the resulting generation of 100 offspring can be "promoted" to be the parents of the next selfed generation. 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.

Click on the buttons below to proceed:

 Parental Generation AA       Aa       aa Offspring Generation AA       Aa       aa
 Parent Gamete 1 Gamete 2 Generation Zygote When no more parents:
When a parent is chosen, it is removed from the Parental Generation histogram. When an offpring is produced, its genotype is shown and also added to the Offspring histogram. Click: to get the effect of clicking the above buttons, in sequence, over and over until the all parents have been selfed. Then the offspring need to be "Promoted" to produce the following offspring generation.

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

Thought Questions

• What pattern of heterozygosity and homozygosity results from inbreeding?
• Is it exactly the same in each run of this exercise?
• How can the heterozygosity and homozygosity in each generation be described?
• Hint: what is F?
• What is the value of F when the population is in H-W proportions?
• Calculate F for each generation
• Graph F over at least 10 generations.
• This exercise starts with 100 individuals and continues with 100 individuals in each generation. What would be different in this process if:
• Instead of starting with 100, and continuing with 100 in each generation, there was a different number?
e.g. 50, or 500?
• After starting with 100, the numbers in succeeding generations was based on the number of offspring per parent?
e.g. 2, or 1/2 (on the average)
• Does the name "single seed descent" indicate that this inbreeding method isn't applicable to animals?