n a limited space. Animals which can be bred experimentally can be subject to reciprocal crosses to reveal genetic influences, and sex-chromosome linkages can be identified by simple crosses (Boake et al, 2002).
Quantitative genetics uses the resemblance among relatives due to shared genotypes to study inheritance patterns (Boake et al, 2002). This gives an estimate of the proportion of phenotypic variation controlled by the genetic effects of additivity, dominance, and forms of epistasis. Resulting estimates of genetic variances and covariances can be used to look at genetic evolution. The analysis of mutants gives valuable genetic information, Profiling gene expression with DNA microassays can link phenotypic variation to genetic factors. Gene homology between species is proving a very useful tool to examine the behavior of specific genes in different species. For example, genetic experiments in Drosophila have identified a male fertility gene, boule, linked to the human gene, deleted-in-azoospermia (DAZ), which has a homologous gene in the mouse as evidenced by the absence of mouse Y-linked DAZ in cloning studies (Burgoyne, 1996).
With Drosophila melanogaster, it is possible to screen for all genes that can mutate and produce a given phenotype (Rubin, 1988). The most commonly used mutations experimentally are those which affect viability, or produce a morphologically recognizable trait. This provides a way of looking at specific gene function. When genes which affect specific processes have been identified, they can be studied by standard methods of genetics. The number of different genes involved in a particular processes can be determined; phenotypes with mutations in more than one gene can be studies to determine hierarchies of gene function; rates of meiotic recombination between a mutation and another gene can be used to map the relative chromosomal position of the mutated gene; using mosaic animals with clo...