Does X chromosome Barr bodies apply to platypus Does X chrom

Solution

Answer:

X inactivation have been mostly studied in placental mammals including mouse and human. Platypus (Monotremes) do not have extensive X inactivation. Platypuses have been seen to follow an XY sex-determination system, with females possessing 5 pairs of X chromosomes as the homogametic sex, and males possessing 5 X and 5 Y chromosomes as the heterogametic sex.

Research on the sex determination of platypuses have revealed that some X-linked genes only expressed an allele from one X chromosomes, while other genes expressed multiple alleles. About half of all X-linked genes seemed to express only one active copy of said gene, alluding to the system of random X-inactivation observed in humans.

These findings suggest that platypuses may employ a hybrid form of dosage compensation that combines feature from both mammals as well as birds.

The recently completed draft genomic sequences of a marsupial (short-tailed opossum) and a monotreme (platypus) have also confirmed the lack of Xist on both X chromosomes. Since, Xist expression is required for barr body formation, so X chromosome barr body should not apply to platypus.