  We updated the agent based Monte Carlo code HERITAGE that simulates human
evolution within restrictive environments such as interstellar, sub-light speed
spacecraft in order to include the effects of population genetics. We
incorporated a simplified -- yet representative -- model of the whole human
genome with 46 chromosomes (23 pairs), containing 2110 building blocks that
simulate genetic elements (loci). Each individual is endowed with his/her own
diploid genome. Each locus can take 10 different allelic (mutated) forms that
can be investigated. To mimic gamete production (sperm and eggs) in human
individuals, we simulate the meiosis process including crossing-over and
unilateral conversions of chromosomal sequences. Mutation of the genetic
information from cosmic ray bombardments is also included. In this first paper
of a series of two, we use the neutral hypothesis: mutations (genetic changes)
have only neutral phenotypic effects (physical manifestations), implying no
natural selection on variations. We will relax this assumption in the second
paper. Under such hypothesis, we demonstrate how the genetic patrimony of
multi-generational crews can be affected by genetic drift and mutations. It
appears that centuries-long deep space travels have small but unavoidable
effects on the genetic composition/diversity of the traveling populations that
herald substantial genetic differentiation on longer time-scales if the annual
equivalent dose of cosmic ray radiation is similar to the Earth radioactivity
background at sea level. For larger doses, genomes in the final populations can
deviate more strongly with significant genetic differentiation that arises
within centuries.
