### person | relative | sibling | twin:

Identical twin
* All identical twins are clones.
* Having the same genetic make-up can be a blessing or a curse.
* Most identical twins have life.
* Most identical twins raise in different environments
  - share identical patterns
* Some identical twins are mirror twins, and their physical traits are mirror images of each other
  - so alike they can wear each other's contact lenses
* Some identical twins have different disease status
  - raise in homes
  - vary in height
* are a clone formed from a single fertilized egg
  - result of the natural separation of an embryo into two identical embryos
  - actually clones of one another because they have the same genetic code
  - also always the same sex
  - always the same sex because they are genetically identical
  - basically clones of each other
  - clones that have happened naturally
* are clones, as are clones of bacteria that reproduce by simple cell division
  - colonies of bacteria that reproduce by simple cell division
  - especially useful for such research because they are genetically the same
  - essentially clones with exactly the same genes
  - genetic carbon copies, but they are separate individuals
* are genetically alike and look extremely similar
  - more similar behaviorally than fraternal twins
* are natural clones as they are exact biological copies of each other
  - from the one fertilized egg
  - normal in a few species
  - one egg cell fertilized by one sperm cell
  - the best possible donors of stem cells
* are the result of a fertilized egg dividing into two
  - one egg joining with one sperm to form the zygote
* are the same genetically, but they are different psychologically and morally
  - sex and the same genetic makeup
  - true clones of each other, with the same genes
  - two people
  - unpredictable and of an unknown genetic makeup
* are very helpful to researchers since they both have the exact same genetic code
  - useful in psychological studies because of their genetic equality
* are, in a sense, clones.
* can be completely different
  - use each other's marrow in a syngeneic transplant
* come from the same egg and sperm which breaks in in two after fertilization.
* develop when a fertilized egg splits
  - single fertilized egg splits in two, leading to two embryos
* differ from fraternal twins in the number of genes they have in common
  - in many respects
* exhibit almost identical brain wave patterns.
* have a higher rate of developing schizophrenia than fraternal twins
  - all the same genes
  - an almost identical character
  - identical genes
  - many similar qualities but are distinct
* have more risks during pregnancy than dizygotic twins
  - similar personalities than fraternal twins reared together
  - separate and distinct bodies
* have the same genetic make up
  - make-up, so they often serve as a focus for research studies
  - twice the chance of being the same as fraternal twins
* look the same because all of their genes are the same
  - but they are different individuals
* make the perfect donors for each other because they are genetically identical.
* occur when a single egg splits in two, creating two babies of the same sex
  - one embryo divides into two genetically identical ones
  - the egg splits after fertilization
* raised completely apart are rarer still.
* result from a single fertilization to form a zygote, which then clones itself
  - when a single fertilized egg divides into two replicas of itself
* separated at birth have some striking differences.
* share all of their genes, and fraternal twins share about half
  - the same genetic make-up and the same family environment
  - virtually all of their genetics
* start as one embryo that splits into two.
* tend to have similar achievement test scores
  - sleep through at almost identical ages
+ Genetics, Tools of Genetics, Twin studies: History of science
  * Identical twins are natural clones. They carry the same genes, they may be used to investigate how much heredity contributes to individual people. Studies with twins have been quite interesting. If we make a list of characteristic traits, we find that they vary in how much they owe to heredity.
+ Identical twins, Twin research: Biological reproduction :: Developmental biology :: Classical genetics
  * Identical twins are natural clones. Because they start out with the same genes, they can be used to investigate how much heredity contributes to individual people. This is the nature vs nurture question
  - Twins in animals
  * Twinning is normal in many mammals, such as rats, cats, dogs. Identical twins are normal in a few species. The nine-banded armadillo, 'Dasypus novemcinctus', gives birth to identical quadruplets. Cyranoski D. 2009. 458', p826.Newman H.H. Patterson J.T. 1909
+ Nature versus nurture, Twin research: Classical genetics :: Social sciences
  * Identical twins are natural clones. Studies with twins have been quite interesting. If we make a list of characteristic traits, we find that they vary greatly in how much they owe to heredity.
+ Skin graft: Surgery :: Tissues
  * Transplants of skin from one person to another is limited by tissue rejection caused by the immune system. Identical twins make the perfect donors for each other because they are genetically identical.