Advances in Genetics Research. Volume 19 extensively reviews a few important aspects of genetic diversity, including: the importance of genetic diversity in livestock and agriculture, the assessment of different procedures to get a precise measure of genetic diversity, factors affecting genetic diversity, and strategies to prevent such losses. Continuing, this compilation discusses genomic instability, which has been observed in several inherited pathological conditions. Mutations causing the disorder, as well as genomic instability, were present in genes associated to different biochemical functions such as: calcium influx or ionic permeation. The authors discuss short sequence repeats or microsatellite markers, which have been utilized extensively in livestock because they can be easily amplified and possess large amounts of allelic variation at each locus. The authors also explore a new commercially available test that can identify fetal chromosomal abnormalities by analyzing fetal nucleic acids circulating in a maternal blood sample. This test can be done before 10 weeks and can replace traditional first-trimester non-invasive screening. The causes underlying inbreeding depression and heterosis are analyzed, allowing for new insights into these phenomena as the result of a diploid genome structure, creating the states of homozygosity and heterozygosity. The relation of inbreeding depression and heterosis to the major biological processes is demonstrated. The closing study discusses default sex from different points of view, proposing a conception "germ cell-supported female default" in vertebrate gonadal somatic cells, as well as the idea that most vertebrate sex-determining genes emerged as destruction factors against the female default.