This is heterozygote advantage, a kind of balance between fierce selection against homozygous sickle-cell sufferers, and selection against the standard HgbA homozygotes by malaria. The heterozygote has a permanent advantage (a higher fitness) so long as malaria exists; and it has existed as a human parasite for a long time. Because the heterozygote survives, so does the HgbS allele survive at a rate much higher than the mutation rate.
Mammals normally produce lactase only as long as the mother has milk. Then the enzyme lactase is cut off. Modern humans are different.
The human ability to drink milk during adult life is supported by a lactase mutation. Human populations have a high proportion of this mutation wherever milk is important to the diet. The spread of milk tolerance is promoted by natural selection: it helps people survive where milk is available.
Genetic studies suggest that the oldest mutations associated with lactase persistence only reached appreciable levels in human populations in the last ten thousand years. Therefore, lactase persistence is often cited as an example of recent human evolution. As lactase persistence is genetic, but animal husbandry a cultural trait, this is gene–culture coevolution.
Ants exhibit a range of polymorphisms. First, there is their characteristic haplodiploid sex determination system, whereby all males are haploid, and all females are diploid.
Second, there is differentiation based mostly on feeding of larvae. This determines, for example, whether the adult is capable of reproduction.
Lastly, there is differentiation of size and 'duties' (particularly of females), which are usually controlled by feeding and/or age, but which may sometimes be genetically controlled. Thus the order exhibits both genetic polymorphism and extensive polyphenism.
An example of a botanical genetic polymorphism is heterostyly, in which flowers occur in different forms with different arrangements of the pistils and the stamens.
Pin and thrum heterostyly occurs in dimorphic species of "Primula", such as "P. vulgaris". There are two types of flower. The pin flower has a long style bearing the stigma at the mouth and the stamens half-way down; and the thrum flower has a short style, so the stigma is half-way up the tube and the stamens are at the mouth.
So when an insect in search of nectar inserts its proboscis into a long-style flower, the pollen from the stamens stick to the proboscis in exactly the part that will later touch the stigma of the short-styled flower, and vice versa.
Another most important property of the heterostyly system is physiological. If thrum pollen is placed on a thrum stigma, or pin pollen on a pin stigma, the reproductive cells are incompatible and relatively little seed is set. Effectively, this ensures outcrossing, as described by Darwin. Quite a lot is now known about the underlying genetics; the system is controlled by a set of closely linked genes; these act as a single unit, a so-called super-gene.
All sections of the genus "Primula" have heterostyle species, altogether 354 species out of 419. Since heterostyly is characteristic of nearly all races or species, the system is at least as old as the genus.
Between 1861 and 1863, Darwin found the same kind of structure in other groups, such as flax ("Linum") and in Purple Loosestrife and other species of "Lythrum".
Heterostyly is known in at least 51 genera of 18 families of Angiosperms.
Studies over many years have shown that natural populations of "Drosophila" are polymorphic for chromosome inversions. The inversions are so common that they must be kept in the population by natural selection.
Kid A
Kid A is the fourth album by the band Radiohead. It was released in October 2000 on the Parlophone label. It was a success, and was certified platinum in the United Kingdom after only one week. "Kid A" was the band's first number one in America, and was named as 'The best album of the 2000s' by Rolling Stone magazine.
All tracks written by Radiohead except where noted.
Hail to the Thief
Hail to the Thief is an album by the band Radiohead. It was released in June 2003.
All songs written by Radiohead.
The King of Limbs
The King of Limbs is an album by the band Radiohead. It was released in 2011. No singles were released from the album, but a video was released for "Lotus Flower". The album got good reviews from critics. PopMatters gave it 9/10 and called it "a beautiful record". It was nominated for five Grammy Awards.
Amnesiac
Amnesiac is an album by the band Radiohead. It was released in June 2001. It went straight to No.1 in the UK Albums Chart. Most critics gave it good reviews. Pitchfork gave it 9/10.
All tracks written by Radiohead.
The Bends
The Bends is an album by the band Radiohead. It was released in April 1995.
All songs written by Radiohead.
Pablo Honey
Pablo Honey is an album by the English alternative rock band Radiohead. It was released in April 1993. Three singles were released from it. "Creep" was released in 1992 and was not successful. In 1993 it was released again and became popular around the world. The album reached No.22 in the UK charts. In 2009 the album was re-released with an extra CD of demos and live songs.
All songs written by Radiohead.
List of SpongeBob SquarePants characters
Below is a list of characters from the television show "SpongeBob SquarePants".
Grace Under Fire
Grace Under Fire was an American television sitcom which aired on ABC between 1993 and 1998. It was part of a wave of 1980s-1990s television shows built around a comedian. Brett Butler starred as Grace, a divorced single mother with three children. This was the highest rated new show for its first season. It was distributed through the Carsey-Werner Company.
Absolution
Absolution is the name of a sacrament of the Roman Catholic, Eastern Orthodox, Anglican and Lutheran churches. Using absolution, a priest or the church can forgive a sin, after confession.
Petrified wood
Petrified wood (from the Greek root Petro meaning "rock" or "stone"; literally "wood turned into stone") is the name given to a special type of fossilized remains of terrestrial vegetation. It is the result of a tree having turned completely into stone by the process of per mineralization. All the organic materials have been replaced with minerals (most often a silicate, such as quartz), while retaining the original structure of the wood. Unlike other types of fossils which are typically impressions or compressions, petrified wood is a three dimensional representation of the original organic material.
The petrifaction process occurs underground, when wood becomes buried under sediment and is initially preserved due to a lack of oxygen which inhibits aerobic decomposition.
Dolores Claiborne (movie)
Dolores Claiborne is a 1995 American crime drama movie set in Maine. Kathy Bates plays the title character. Also starring in the movie is Jennifer Jason Leigh, who plays her daughter. Dolores is accused of murdering her employer, an elderly woman. Dolores is also accused of murdering her husband. He was a violent alcoholic sexually abusing her daughter.
This movie is based on Stephen King's novel of the same name.
Christian de Duve
Christian René, viscount de Duve (2 October 1917 – 4 May 2013) was a Belgian biochemist. He was born in Thames Ditton, Surrey and grew up in Antwerp, Belgium.
Duve won the Nobel Prize in Physiology or Medicine in 1974. He discovered two cell organelles, lysosomes and peroxisomes. He described them, and was the first to investigate their functions. Duve shared the Nobel prize with Albert Claude and George E. Palade.
De Duve died in Grez-Doiceau, Belgium, on 4 May 2013, when he asked that his life be ended through euthanasia.
Corvus (constellation)