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 normal diploid number of chromosomes is constant for each species. For humans, the diploid number is 46 (23 pairs in all somatic cells). In the formation of gametes (ovum and spermatozoon), the number is reduced to one half (haploid number); i.e., the ovum and sperm each contain 23 chromosomes. Of these, 22 are autosomes and one is the sex chromosome (X or Y).