User:Barbara (WVS)/ sandbox Chicken genome

The chicken genome is the code and description of the genes and traits of the chicken. The chicken genome sequence is considered important for several reasons. One reason for this is that the chicken provides a major protein source globally. Determing the chicken's gene sequence will be benefitial to agricultural science. It is the first bird species to be sequenced. The chicken may have 20,000–23,000 genes;

The genome of the chicken differs significantly from that of humans. Only 2.5% of the chicken genome maches that of humans. The size of the chicke genome is much smaller than that of the mouse or humans.

Further investigations into the chicken genome are anticipated to address the negative traits that have developed in chickens during their long history of breeding. Chickens that are raised for their meat have a number of congenital disorders that effect their health. These are reduced fertility, accumulation of internal body fluid in their abdoments, decreased resistance to pathogens and lameness. Chickens that are used for producing eggs have the tendency to develop osteoporosis..

Academic support for sequencing the genome of chickens has been the US National Health Institute.

Chickens have a diploid number of 78 (2n = 78) chromosomes, and as is usual in birds, the majority are microchromosomes. Classification of chicken chromosomes varies by author. Some classify them as 6 pairs of macrochromosomes, one pair of sex chromosomes, with the remaining 32 pairs being intermediate or microchromosomes. Other arrangements such as that used by the International Chicken Genome Sequencing Consortium include five pairs of macrochromosomes, five pairs of intermediate chromosomes, and twenty-eight pairs of microchromosomes. Microchromosomes represent approximately one third of the total genome size, and have been found to have a much higher gene density than macrochromosomes. Because of this, it is estimated that the majority of genes are located on microchromosomes, though due to the difficulty in physically identifying microchromosomes and the lack of microsatellite markers, it has been difficult to place genes on specific microchromosomes.

Replication timing and recombination rates have been found to differ between microchromosomes and macrochromosomes in chickens. Microchromosomes replicate earlier in the S phase of interphase than macrochromosomes. Recombination rates have also been found to be higher on microchromosomes. Possibly due to the high recombination rates, chicken chromosome 16 (a microchromosome) has been found to contain the most genetic diversity of any chromosome in certain chicken breeds. This is likely due to the presence on this chromosome of the major histocompatibility complex (MHC).

For the many small linkage groups in the chicken genome which have not been placed on chromosomes, the assumption has been made that they are located on the microchromosomes. Interestingly, groups of these correspond almost exactly with large sections of certain human chromosomes. For example, linkage groups E29C09W09, E21E31C25W12, E48C28W13W27, E41W17, E54 and E49C20W21 correspond with chromosome 7.