that needs further study. One of the more recent models of inversions is the Kirkpatrick and Barton Model (2006), which states that inversions are selectively advantageous by linking together adaptive alleles. This is in contrast to non-inverted regions, which may allow adaptive and maladaptive alleles to be carried. Also, inversions may be used as detectors for global climate change. In Drosophila melanogaster , a study done in 2015 showed that a specific inversion (3R) may contribute to adaptions to climate change. In the species Drosophila subobscura, researchers have been able to track global climate change by measuring the magnitude and directional shift in chromosome inversion frequencies, relative to temperatures at specific global sites. Effects on recombination When an inversion carrying chromosome is paired with a non-inverted homologous chromosome (Inversion heterozygotes) during meiosis, they fail to synapse properly and inversion loops are formed. A crossing-over within the loop can produce unbalanced gametes. In a paracentric inversion, recombination results in one dicentric chromatid and one acentric chromatid. During Anaphase, both recombinants are faced with problems. The acentric chromatid is pulled to one pole or the other, and the dicentric recombinant generates dicentric bridges as it is pulled in two directions. In a pericentric inversion, similar imbalanced chromosomes are produced. The recombinant chromosomes resulting from these crosses include deletions and duplications. The offspring produced by such gametes are mostly inviable, and therefore, recombination is indirectly suppressed within inverted regions. Evolutionary consequences The suppressed recombination between inversion heterozygotes provides an opportunity for the independent evolution of the ancestral and inverted arrangements. At the beginning, the inverted arrangement lacks variation, while the ancestral one does not. If the inverted haplotype is not lost (eg. due to drift), the variation in the inverted arrangement is increased over time, and recombination rate in the inverted region is somewhat restored as more homozygotes are introduced. Inversion polymorphism can be established in two ways. Genetic drift or selection can result in fixation of an inversion in a local population. Inversion polymorphism can result from gene flow between this population and a population without the inversion. Balancing selection can also result in inversion polymorphism by frequency dependence or overdominance. The fitness differences between the inverted and the ancestral chromosome can either produce a stable polymorphism or can result in the fixation of one or the other chromosome. Inversions have been essential to sex chromosome evolution. In mammals, The Y chromosome