SUMMARY / RELATED TOPICS

Sex linkage

Sex linkage describes the sex-specific patterns of inheritance and presentation when a gene mutation is present on a sex chromosome rather than a non-sex chromosome. In humans, these are termed X-linked dominant and Y-linked; the inheritance and presentation of all three differ depending on the sex of both the parent and the child. This recessiveness. There are many more X-linked conditions than Y-linked conditions, since humans have several times as many genes on the X chromosome than the Y chromosome. Only females are able to be carriers for X-linked conditions; as such, X-linked recessive conditions affect males much more than females. In X-linked recessive inheritance, a son born to a carrier mother and an unaffected father has a 50% chance of being affected, while a daughter has a 50% chance of being a carrier, however a fraction of carriers may display a milder form of the condition due to a phenomenon known as skewed X-inactivation, in which the normal process of inactivating half of the female body's X chromosomes preferably targets a certain parent's X chromosome.

If the father is affected, the son will not be affected, as he does not inherit the father's X chromosome, but the daughter will always be a carrier. In X-linked dominant inheritance, a son or daughter born to an affected mother and an unaffected father both have a 50% chance of being affected. If the father is affected, the son will always be unaffected, but the daughter will always be affected. A Y-linked condition will only be inherited from father to son and will always affect every generation; the inheritance patterns are different in animals that use sex-determination systems other than XY. In the ZW sex-determination system used by birds, the mammalian pattern is reversed, since the male is the homogametic sex and the female is heterogametic. In classical genetics, a mating experiment called a reciprocal cross is performed to test if an animal's trait is sex-linked; each child of a mother affected with an X-linked dominant trait has a 50% chance of inheriting the mutation and thus being affected with the disorder.

If only the father is affected, 100% of the daughters will be affected, since they inherit their father's X chromosome, 0% of the sons will be affected, since they inherit their father's Y chromosome. There are less X-linked dominant conditions than X-linked recessive, because dominance in X-linkage requires the condition to present in females with only a fraction of the reduction in gene expression of autosomal dominance, since half of a particular parent's X chromosomes are inactivated in females. Alport syndrome Coffin–Lowry syndrome Fragile X syndrome Idiopathic hypoparathyroidism Incontinentia pigmenti Rett syndrome Vitamin D resistant rickets Females possessing one X-linked recessive mutation are considered carriers and will not manifest clinical symptoms of the disorder, although differences in X chromosome inactivation can lead to varying degrees of clinical expression in carrier females since some cells will express one X allele and some will express the other. All males possessing an X-linked recessive mutation will be affected, since males have only a single X chromosome and therefore have only one copy of X-linked genes.

All offspring of a carrier female have a 50% chance of inheriting the mutation if the father does not carry the recessive allele. All female children of an affected father will be carriers, as daughters possess their father's X chromosome. If the mother is not a carrier, no male children of an affected father will be affected, as males only inherit their father's Y chromosome; the incidence of X-linked recessive conditions in females is the square of that in males: for example, if 1 in 20 males in a human population are red–green color blind 1 in 400 females in the population are expected to be color-blind *. Aarskog–Scott syndrome Adrenoleukodystrophy Bruton's agammaglobulinemia Color blindness Complete androgen insensitivity syndrome Congenital aqueductal stenosis Duchenne muscular dystrophy Fabry disease Glucose-6-phosphate dehydrogenase deficiency Haemophilia A and B Hunter syndrome Inherited nephrogenic diabetes insipidus Menkes disease Ornithine carbamoyltransferase deficiency Wiskott–Aldrich syndrome Various failures in the SRY genes White eyes in Drosophila melanogaster flies—the first sex-linked gene discovered.

Fur color in domestic cats: the gene that causes orange pigment is on the X chromosome. The first sex-linked gene discovered was the "lacticolor" X-linked recessive gene in the moth Abraxas grossulariata by Leonard Doncaster, it is important to distinguish between sex-linked characters, which are controlled by genes on sex chromosomes, two other categories. Sex-influenced or sex-conditioned traits are phenotypes affected by whether they appear in a male or female body. In a homozygous dominant or recessive female the condition may not be expressed fully. Example: baldness in humans; these are characters only expressed in one sex. They may be caused by genes on either sex chromosomes. Examples: female sterility

USS Breakwater (SP-681)

USS Breakwater was a United States Navy patrol vessel and tug in commission from 1917 to 1920. Breakwater was built as a wooden-hulled, single-screw commercial steam fishing trawler of the same name at Milton, Delaware, in 1907. In the spring of 1917, the U. S. Navy purchased her from the Lewes Fishing Company of Lewes, for use during World War I. Assigned the section patrol number 681, she was commissioned at the Philadelphia Navy Yard in Philadelphia, Pennsylvania, on 12 May 1917 as USS Breakwater. Assigned to the 4th Naval District, Breakwater operated as a patrol vessel and tug for the remainder of World War I and into the summer of 1919. On 15 July 1919, Breakwater was assigned to Submarine Division 1 at Coco Solo in the Panama Canal Zone; that day, she received orders to assemble at Cape May, New Jersey, with the patrol vessels USS F. Mansfield and Sons Co. and USS SP-467 at "the earliest practicable date and when ready proceed in company by Canal Zone to assigned stations." Breakwater reached her station in the Canal Zone and operated out of Coco Solo as a utility vessel with Submarine Division 1.

Drydocked in the spring of 1920, Breakwater was found to be in poor shape, a board of inspection and survey condemned her. She was decommissioned at Coco Solo on 8 September 1920 and was sold to the Panama Construction Company on 8 April 1921; this article incorporates text from the public domain Dictionary of American Naval Fighting Ships. The entry can be found here. Department of the Navy Naval History and Heritage Command Online Library of Selected Images: U. S. Navy Ships: USS Breakwater, 1917-1921 NavSource Online: Section Patrol Craft Photo Archive Breakwater

Hog Island (Michigan)

Hog Island, an uninhabited 2,075-acre island in Lake Michigan, is the fourth largest island in the Beaver Island archipelago. It is owned by the U. S. state of Michigan as part of the Beaver Islands State Wildlife Research Area and is administered by the Michigan Department of Natural Resources. Hog Island is part of the Beaver Island archipelago, a cluster of islands in the northern portion of Lake Michigan; these islands are composed of erosion-resistant rock that protruded above the water after retreating glaciers had carved out the basin that holds Lake Michigan. Hog Island is 4 miles long in a north-south direction, lies off the shore of Emmet County, Michigan, its low, swampy terrain is of significant interest to naturalists because it is one of the least-disturbed islands in Lake Michigan. Hog Island is difficult to reach by boat. There is point access from Hog Island Point State Forest, located just off US Highway 2, seven miles from Naubinway, Michigan; the island's wetlands are important spawning grounds for yellow perch and smallmouth bass, as well as lake birds that feed on fish, such as the common tern, listed as threatened within Michigan.

Three endemic riparian plant species, Houghton's goldenrod, the Lake Huron tansy, Pitcher's thistle, have been identified on Hog Island. All three plants are listed as threatened within Michigan. Old-growth northern hardwood and boreal softwood groves exist on the island