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.
Two major places where astronomers see accretion disks are in binary star systems (two stars orbiting each other) and active galactic nuclei. I will discuss an accretion disk in a binary star system, but the basic ideas are the same for all cases. If one star in a binary system is a compact object such as a very dense white dwarf star and the other star is a normal star like the Sun, the white dwarf can pull gas off the normal star and accrete it onto itself.