Bloodstain shape is determined by the angle between the flight path of the droplet and the surface that it impacts (Fig.1). When a drop of blood strikes a horizontal surface from the perpendicular (at an angle of 90°, Fig.2), the resulting bloodstain will be round. As the angle between the blood drops’ flight path and the target surface decreases, the length of the resulting bloodstain increases and the width decreases; in other words, the bloodstain becomes longer and narrower as the size of the angle decreases (Fig.3). A blood drop that has impacted a target surface from an angle of 12° will be long and narrow (Fig.4). Also present on these long, narrow stains is a ‘tail’ (Fig. 4). As the drop of blood impacts the target surface, the main body of the droplet will stick to the surface. A small portion of the blood drop will tear off from the top and continue in a forward direction. This secondary spatter has the appearance of a tail.
DNA strands are split apart to allow an opening for replication. The
opening has two replication forks so synthesis goes toward them in 5' to
3' direction.
