Describe and summarize any similarity of the human X chromos

Describe and summarize any similarity of the human X chromosome with chromosomes from, oh lets see here, chickens. Yeah, chickens. What does your essay suggest about the origin of the human X chromosome?

Solution

Human X chromosome shows some similarities with the chicken Z chromosome. The sex chromosomes in humans are XX (female) and XY (male) while in birds they are ZW and ZZ respectively. The W and Y chromosomes of birds and humans are thought to be eolved from the autosomes. The common X chromosome in both sexes in humans and Z chromosome in both sexes of birds might have evolved from the ancestor by convergent evolution. The Z chromosome is orhtologous to human X chromosome and this can be evident by sequencing of chicken Z chromosome. But, comparitive sequencig of 30 Z linked genes proved that the chicken Z chromosome is orthologous to autosomes 5, 8, 9 and 18 but not to human X chromosome. Some speculation about origin of human X chromsome and chicken\'s Z chromosome propose that they have a common origin. The comparitive gene mapping results propose that the chicken Z and human X were derived from different parts of an ancestral proto sex chromosome that was broken apart, leaving Z orthologs autosomal in mammals and X orthologs autosomal in birds.