162
Xenopus
FIGURE 10.2 Structures of the W- and Z-specifc regions and the Hox clusters. (A) W- and Z-specifc regions at XLA2Lq32–33 are
indicated by magenta and blue lines and correspond to the W and Z chromosomes, respectively. The fanking regions on the left and
right sides (black lines) are shared between the W and Z chromosomes and harbor olfactory receptor (or) or cdk4 genes. Modif ed from
(Mawaribuchi et al., 2017). (B) Comparison of Hox clusters between X. tropicalis and X. laevis. X. tropicalis has four clusters (Hox
A, HoxB, HoxC, and HoxD), while X. laevis has four each in the L and S subgenomes (indicated with “.L” and “.S”). hox genes of 13
paralogous groups are present. All hox genes are retained in X. laevis after allotetraploidization, but for hoxb2.L, which is pseudogenized
(indicated as “p”).
Source: Modifed from (Kondo et al., 2017).
10.3.2. ANALYSES OF HOX GENES
to four through two rounds of WGD in the vertebrate lineage (reviewed in Holland, 2013). Thus, cartilaginous f shes,
The hox genes and the Hox clusters are often identif ed and bony fshes, and tetrapods have four Hox clusters in their
characterized for genome analysis or evolutionary studies. genome. An additional third round of WGD occurred in the
hox genes encode transcription factors, and in the genome teleost lineage; this was initially proposed based on the exisof most animals, these genes are clustered in a specif c tence of short duplicated segments of gene synteny in the
region called the Hox cluster. The genes and the structure teleost genomes (Aparicio et al., 2002; Meyer and Van de
of the clusters are well conserved in bilaterians. While the Peer, 2005). The strongest evidence for the third round of
chordate ancestor had a single Hox cluster as in the cepha- WGD is that teleosts have seven to eight Hox clusters. Most
lochordate Branchiostoma foridae ( Garcia-Fernández and teleosts examined have seven clusters by losing one of the
Holland, 1994), the number of Hox clusters has increased two HoxC clusters in the lineage including medaka f sh and
Xenopus
FIGURE 10.2 Structures of the W- and Z-specifc regions and the Hox clusters. (A) W- and Z-specifc regions at XLA2Lq32–33 are
indicated by magenta and blue lines and correspond to the W and Z chromosomes, respectively. The fanking regions on the left and
right sides (black lines) are shared between the W and Z chromosomes and harbor olfactory receptor (or) or cdk4 genes. Modif ed from
(Mawaribuchi et al., 2017). (B) Comparison of Hox clusters between X. tropicalis and X. laevis. X. tropicalis has four clusters (Hox
A, HoxB, HoxC, and HoxD), while X. laevis has four each in the L and S subgenomes (indicated with “.L” and “.S”). hox genes of 13
paralogous groups are present. All hox genes are retained in X. laevis after allotetraploidization, but for hoxb2.L, which is pseudogenized
(indicated as “p”).
Source: Modifed from (Kondo et al., 2017).
10.3.2. ANALYSES OF HOX GENES
to four through two rounds of WGD in the vertebrate lineage (reviewed in Holland, 2013). Thus, cartilaginous f shes,
The hox genes and the Hox clusters are often identif ed and bony fshes, and tetrapods have four Hox clusters in their
characterized for genome analysis or evolutionary studies. genome. An additional third round of WGD occurred in the
hox genes encode transcription factors, and in the genome teleost lineage; this was initially proposed based on the exisof most animals, these genes are clustered in a specif c tence of short duplicated segments of gene synteny in the
region called the Hox cluster. The genes and the structure teleost genomes (Aparicio et al., 2002; Meyer and Van de
of the clusters are well conserved in bilaterians. While the Peer, 2005). The strongest evidence for the third round of
chordate ancestor had a single Hox cluster as in the cepha- WGD is that teleosts have seven to eight Hox clusters. Most
lochordate Branchiostoma foridae ( Garcia-Fernández and teleosts examined have seven clusters by losing one of the
Holland, 1994), the number of Hox clusters has increased two HoxC clusters in the lineage including medaka f sh and