Ash, green, and red (Fraxinus spp.)âThe common. leaf spot and scorch on ash leaves is caused by the ash. anthracnose fungus, Gloeosporium aridum. Large areas of. infected leaves, especially along the edges, turn brown (Figure. 2). Premature leaf drop may occur.
How sperm and eggs develop precisely 23 chromosomes each. April 12, 2012. There are many tools that cells could use to separate DNA strands that cross over during meiosis. UC Davis researchers have identified the right tools for the job. Researchers at the University of California, Davis have discovered a key tool that helps sperm and eggs develop exactly 23 chromosomes each.
The sperm contains one copy of each of the 22 autosomal chromosomes and either one X or one Y chromosome. After fusion, these pair up to form a diploid cell, so that there are 46 chromosomes-two of each of the 22 autosomal chromosomes, and either two X chromosomes, or one X and one Y chromosome.