How to Grow Butter Leaf Lettuce. Butter lettuce is a loose-leaf lettuce with a mild flavor. Lettuce is a cool-weather crop, grown across the U.S. in the spring and fall when temperatures are moderate. Butter lettuce, a loose-leaf type of lettuce, may be more tolerant of hot temperatures than some other varieties. In maritime climates with cool summers, lettuce may be grown in the summer, fall and late winter. Inland, where temperatures rise in the summer, lettuce may be grown in late winter and fall.
Humans have 23 pairs of chromosomes, one half of each pair inherited from each parent. The Y chromosome is small, carries few genes, and has abundant repetitive sequence, while the X chromosome is more autosome-like in form and content.
A chromosome is a DNA molecule with part or all of the genetic material of an organism. Chromosomes are normally visible under a light microscope only when the cell is undergoing the metaphase of cell division. Before this happens, every chromosome is copied once, and the copy is joined to the original by a centromere, resulting in an X-shaped structure. The original chromosome and the copy are now called sister chromatids. During metaphase the X-shape structure is called a metaphase chromosome.