The (Bromham et al. 1996). Alongside this,The (Bromham et al. 1996). Alongside this,

The first explanation involves
the mutation rate between species, specifically mutations within DNA
replication. In vertebrate lineages, species with a shorter generation time
have faster rates of molecular evolution as they replicate more often per unit
time. (Bromham et al. 1996). Alongside this, the number of DNA
replications per generation can vary; in gamete production it will take fewer
cell generations to make Zebrafish ova as compared to Human ova (Bromham and
Leys. 2005). In relation to Figure 7, in lower vertebrates, there is more
variation of genes when compared to the Human and Mouse which appear more
conserved. An example of this is: the SEMA6D
gene which only appears in Zebrafish and Xenopus, as well as the two novel
sequences in Chickens and Xenopus. Furthermore, gene insertions shape genetic
and phenotypic diversity. (Yan, Y., et
al. 2014). They can account for a shift in order of genes or introduction
of novel genes, as shown in Figure 7 by the addition of GM9913 in the Mouse genome.

Transposition of genes can
account for changes in genome size, sequence and expression during speciation
and evolution. The trigger for transposition induced changes can be stress
applied (predation), and can produce genetic alterations once inserted. These
can include: insertions, excisions, translocations in the insert region and
duplications. (Clegg M T., et al.
2003). Furthermore, transposable elements can participate in the
re-organisation of the genome, through mobilisation of non- transposable
elements or as substrates for recombination. This recombination would occur by homology between two
sequences located in the same or different chromosomes, resulting in
chromosomal alterations (Kidwell, et al.
2001). In relation to
Figure 7, the region of: DUT – SLC12A1 –
CTXN2 – MYEF2 – SLC24A5 is on the left of the gene in Zebrafish, but is
fully conserved on the right side of the gene in Human, Mouse and Chicken. 

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Chromosomal translocation can also
support the conservation of single genes between species- not necessarily by
position but by presence. Chromosomal
rearrangements can encompass: deletions, duplications, inversions and
translocations. Each of these can be caused by DNA double
helices breakage in the genome at
two locations, followed by re-joining of the broken ends to produce a new
arrangement of genes, different from the gene order
of the chromosomes before. Specifically, inversions being balanced
rearrangements so do not change the amount of genetic material, but the order
of the genes. (Griffiths., et al. 1999). Therefore, this could imply that each species
share the same set of genes but whether they are upstream or downstream to the
FBN1 gene is not known.