These studies are now being done by GWAS in 2 patient groups, examining both baseline HbF and the HbF response to hydroxyurea. Genetic modulation of sickle cell disease: Homozygosity for a single Î²-globin gene mutation (HBB; glu6val) causes sickle cell anemia.hese studies are now being done by GWAS in 2 patient groups, examining both baseline HbF and the HbF response to hydroxyurea. Genetic modulation of sickle cell disease: Homozygosity for a single Î²-globin gene mutation (HBB; glu6val) causes sickle cell anemia.
Spiral Galaxies. Spiral galaxy M100. Spiral galaxies have three main components: a bulge, disk, and halo (see right). The bulge is a spherical structure found in the center of the galaxy. This feature mostly contains older stars. The disk is made up of dust, gas, and younger stars. The disk forms arm structures.
Structure and Composition. The galaxy we live in, called the Milky Way Galaxy, is a barred spiral galaxy composed of at least 100 billion stars. It is approximately 100,000 light years across and about 1000 light years thick. It has a central bulge that is about 10,000 light years in diameter.