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Bird Breeder

[screen shot]

If you download the NetLogo application, this model is included. (You can also run this model in your browser, but we don't recommend it; details here.)


This is a model of a selective breeding program of birds (or dragons). In the scenario presented in the model the user assumes the role of a bird breeder, whose goal is breed a line of "fancy" looking birds or a specific type of dragon through managing a selective breeding program.


In the "birds" scenario the user breeds have a simple genetic representation for five traits: Crest color, wing color, breast color, tail color, and sex.

In the "birds" scenario these traits are represented with genes that have one of two possible alleles each (A and a, B and b, C and c, D and d, and W and Z, respectively). Upper case letters represent dominant genes and lower case represent recessive genes. Therefore the three combinations AA, Aa, and aA result in expression of the trait for A (e.g. gray crest), and only aa results in the expression of the trait for a (e.g. red crest). Males and Females are determined by whether the bird has ZZ (male) or WZ (female) genetic information. One trait, crest color, is sex linked. Male birds (ZZ) display a crest on their head, while females (WZ) do not (though they still carry the genetic information for how it should be expressed if they were male).

In the "dragons" scenario the user breeds have a simple genetic representation for four traits: body color, breath type, breast color, tail shape, and sex.

In the "dragons" scenario these traits are represented with genes that have one of two possible alleles each (A and a, B and b, C and c, D and d, and W and Z, respectively). Females and males can be distinguished by the shape of their wings. Upper case letters do not represent dominant genes in this scenario. Gene expression follows rules for co-dominance, where both genes are expressed, resulting in a mixed or dual expression of the genes. For example, A represents yellow coloring, a represents red coloring, so AA will be expressed as yellow, Aa will be expressed as orange, aA also will be expressed as orange, and aa will be expressed as red.

Here is the genotype to phenotype maps for both scenarios:

Bird Scenario: Crest color: (AA, Aa, aA) grey or (aa) blue Wing color: (BB, Bb, bB) grey or (bb) red

Breast color: (CC, Cc, cC) grey or (cc) purple Tail color: (DD, Dd, dD) grey or (dd) red

Dragon Scenario: Body color: (AA) yellow or (Aa, aA) orange or (aa) red

Breath type: (BB) frost breath or (Bb, bB) steam breath or (bb) fire breath

Breast color: (CC) black or (Cc, cC) grey or (cc) white

Tail shape: (DD) spade or (Dd, dD) rope and spade or (dd) rope


There are 4 players in this selective breeding scenario and you are one of them. The other three are computer players. Each of the computer players take a passive role in the breeding of birds, but serve as sources for out-breeding your own stock of birds. You start with 3 birds you own in your six cages (at the bottom of the world).] There are 6 breeding locations (color coded) in the middle of the world. When move (using your mouse) one male and one female bird into a breeding location and press BREED-BIRDS, eggs will hatch. You may drag the eggs back to your cages to see what the birds look like and keep them. To set a bird free, just click drag it into the white space in the world and release the mouse button. You can only set birds free that you own.

You start with $500 and are trying to earn at least the target $ reward for success (set with the slider REWARD-FOR-SUCCESS. Each breeding event also has an assigned cost $ (COST-FOR-BREEDING). If you wish to breed your birds with another player's, you may press the REQUEST CONTRIBUTION BIRDS button. This will cost COST-CONTRIBUTION (set by this slider) for each bird contributed.

Initial settings (chooser): - SCENARIO: chooser that determines whether you will be breeding "birds" or "dragons".

Buttons: - SETUP: Press this first to assign the SCENARIO you will be playing - GO: Press this second to start the breeding challenge

  • NEXT INSTRUCTION: Use this to display a series of instructions about how to user the interface and mouse interactions with the birds.

  • REQUEST CONTRIBUTION BIRDS FOR BREEDING: When pressed one bird from each computer player is loaned for breeding to one of the top three breeding sites.

  • BREED CURRENT BIRDS AT BREEDING SITE: When pressed, all breeding sites that have at least one male and one female in them will produce a set of eggs in the remaining available spaces (up to four at that breeding site). If more than one male or females are at that site, only one female and male will breed.
  • REMOVE ALL EGGS FROM BREEDING SITES: Removes all eggs currently in all breeding sites.
  • SELL GOAL BIRD: Attempts to sell the bird you have been trying to breed. This will generate either a warning (if you don't have the bird yet in your cages) or a reward message if you do have the bird. If you have the bird, the bird is removed from your cages and you will be given $, set by the REWARD-FOR-GOAL-BIRD slider.

Sliders: - COST-BREEDING: cost in $ for every pair of birds that you breed. - COST-CONTRIBUTION: cost in $ of pressing the REQUEST CONTRIBUTION BIRDS. - REWARD-FOR-GOAL-BIRD: $ rewarded for selling one goal bird.

Switches: - SHOW-GENETICS?: Show the Mendelian representation of the genes that each bird or egg has.

Monitors: - Your funds $: Shows the money you currently have in your bank account.


Even though birds produce four eggs when they mate, the four eggs may or may not produce the expected probabilities of a theoretical Punnett square. This is because, of course that expected probabilities, represent what would result after an infinite set of crosses.


See if you can breed for the fancy bird in the least number of generations.

Write down the breeding plan you followed to create a line of the fancy bird. Create a pedigree diagram to show the series of generations and breeding events that led to the fancy bird.


The model shows two different scenarios, "birds" and "dragons". Other possible could be added such as virtual dogs, cats, corn, etc...

The model could be extended to a HubNet version, where all four players are active competitors in the selective breeding challenge.


Plant Hybridization model.


This model is part of the BEAGLE curriculum (


If you mention this model or the NetLogo software in a publication, we ask that you include the citations below.

For the model itself:

Please cite the NetLogo software as:


Copyright 2007 Uri Wilensky.


This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 License. To view a copy of this license, visit or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA.

Commercial licenses are also available. To inquire about commercial licenses, please contact Uri Wilensky at

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