The inclusion of a set of tiny chromosomes was recognized early and thought to plant sex determination and sex chromosomes pictures in Adelaide You a reptilian feature [ 3 ], but this suggestion was later refuted [ 4 ]. Wide genome comparisons reveal the origins of the human X chromosome.
The contradiction with early gene mapping of several human X orthologs to platypus X 1 led us to further investigate the location of human X orthologs in the platypus genome. The chicken Z is homologous to regions of human chromosomes 9 and 5. Five paints identified X chromosomes present in single copy in males but two copies in females, and five paints identified Y chromosomes that were present only in males.
The order of the first five chromosomes of the chain can be deduced from the homology relationships as X 1 Y 1 X 2 Y 2 X 3.
Orthologs of genes in the conserved region of the human X including SOX3the gene from which SRY evolved all map to platypus chromosome 6, which therefore represents the ancestral autosome from which the therian X and Y pair derived. Vice versathere are also four echidna chromosomes Tac plant sex determination and sex chromosomes pictures in Adelaide You, 7, 9, 12 each of whose arms are homologous to two platypus chromosomes, implying either fissions in the platypus lineage or fusions in the echidna lineage Figures 6 and 7c.
Email the editor. Chromosome painting reveals a meiotic chain of nine sex chromosomes in the male echidna and establishes their order in the chain. Figure 7.
Thirty-two of these BACs that apparently mapped to platypus X chromosomes were then examined further in the present study. Cytogenet Cell Genet. Sex determination systems in plants have evolved many times from hermaphroditic ancestors including monoecious plants with separate male and female flowers on the same individualand sex chromosome systems have arisen several times in flowering plant evolution.
Genome Biol 8, R However, the presence of a strongly hybridizing region on the larger echidna Y 3 using the platypus Y 5 paint suggests that the content of this platypus Y is incorporated into echidnaY 3. Chromosomes 3, 6, and X 5 contain the NOR regions. Tac chromosome paints hybridized to male Oan metaphases.
Author information Article notes Copyright and License information Disclaimer. The ten sex chromosomes form a multivalent chain at meiosis held together by chiasmata within homologous pairing regions.