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Population dynamics: single species: sexual reproduction

Model : super_x
Simile version : 3.1+
Date added : 2003-09-11
Keywords : Population dynamics ; Individual-based ; Association submodel ; Inheritance ;

Description

This is a model of a population of sexually reproducing organisms, for testing the theoretical possibility of wiping out a species by introducing a “Super X” chromosome.

Each individual has two sets of chromosomes, one inherited from each parent. Each time step they create a gamete, consisting of a set of chromosomes taken at random from one parent or the other. If a female mates she becomes pregnant, collecting the gamete from her partner. This is kept until she gives birth, when it is passed on to the new individual together with a gamete of her own. Sex of a new individual is determined by whether they inherit an X (<3) or Y (>=3) chromosome from their father.

Individuals can die through old age or overcrowding. Sexually mature males are ordered according to their age, and each non-pregnant sexually mature female picks one at random to mate with.

At the beginning 10% of the individuals are “super x” mutants. This is a mutation on the X chromosome (<0) that in males prevents the formation of sperm carrying a Y chromosome. It has no effect in females. The theory goes that Super X will spread through the population, since if a male has it it will be inherited by all their offspring rather than just half like any other gene. Furthermore, once it has spread, no more males will be born, and the species will become extinct.

The model bears out this theory, suggesting the possibility of engineering Super X genes in order to wipe out species detrimental to human health. But it might not be a good idea to try this on the anopheles mosquito, since in the short term many more females are produced — and it is these which carry malaria.

Files

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sex.sml

Diagram

Equations

Equation listing

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