Two off-spring from the same PREGNANCY. They are from a single fertilized OVUM that split into two EMBRYOS. Such twins are usually genetically identical and of the same sex.

The division of a ZYGOTE into two parts, each of which is capable of further development.

Disorders affecting TWINS, one or both, at any age.

Two offspring from the same PREGNANCY. They are from two OVA, fertilized at about the same time by two SPERMATOZOA. Such twins are genetically distinct and can be of different sexes.

Two individuals derived from two FETUSES that were fertilized at or about the same time, developed in the UTERUS simultaneously, and born to the same mother. Twins are either monozygotic (TWINS, MONOZYGOTIC) or dizygotic (TWINS, DIZYGOTIC).

Methods of detecting genetic etiology in human traits. The basic premise of twin studies is that monozygotic twins, being formed by the division of a single fertilized ovum, carry identical genes, while dizygotic twins, being formed by the fertilization of two ova by two different spermatozoa, are genetically no more similar than two siblings born after separate pregnancies. (Last, J.M., A Dictionary of Epidemiology, 2d ed)

Three individuals derived from three FETUSES that were fertilized at or about the same time, developed in the UTERUS simultaneously, and born to the same mother.

The study of the patterns of ridges of the skin of the fingers, palms, toes, and soles.

The external elements and conditions which surround, influence, and affect the life and development of an organism or population.

Four individuals derived from four FETUSES that were fertilized at or about the same time, developed in the UTERUS simultaneously, and born to the same mother.

The condition of carrying two or more FETUSES simultaneously.

Five individuals derived from five FETUSES that were fertilized at or about the same time, developed in the UTERUS simultaneously, and born to the same mother.

The status during which female mammals carry their developing young (EMBRYOS or FETUSES) in utero before birth, beginning from FERTILIZATION to BIRTH.

The outward appearance of the individual. It is the product of interactions between genes, and between the GENOTYPE and the environment.

The occurrence in an individual of two or more cell populations of different chromosomal constitutions, derived from a single ZYGOTE, as opposed to CHIMERISM in which the different cell populations are derived from more than one zygote.

The different ways GENES and their ALLELES interact during the transmission of genetic traits that effect the outcome of GENE EXPRESSION.

A latent susceptibility to disease at the genetic level, which may be activated under certain conditions.

The transfer of mammalian embryos from an in vivo or in vitro environment to a suitable host to improve pregnancy or gestational outcome in human or animal. In human fertility treatment programs, preimplantation embryos ranging from the 4-cell stage to the blastocyst stage are transferred to the uterine cavity between 3-5 days after FERTILIZATION IN VITRO.

The transmission of traits encoded in GENES from parent to offspring.

The performance of dissections, injections, surgery, etc., by the use of micromanipulators (attachments to a microscope) that manipulate tiny instruments.

A syndrome of defective gonadal development in phenotypic females associated with the karyotype 45,X (or 45,XO). Patients generally are of short stature with undifferentiated GONADS (streak gonads), SEXUAL INFANTILISM, HYPOGONADISM, webbing of the neck, cubitus valgus, elevated GONADOTROPINS, decreased ESTRADIOL level in blood, and CONGENITAL HEART DEFECTS. NOONAN SYNDROME (also called Pseudo-Turner Syndrome and Male Turner Syndrome) resembles this disorder; however, it occurs in males and females with a normal karyotype and is inherited as an autosomal dominant.

The systems and processes involved in the establishment, support, management, and operation of registers, e.g., disease registers.

Sets of cell surface antigens located on BLOOD CELLS. They are usually membrane GLYCOPROTEINS or GLYCOLIPIDS that are antigenically distinguished by their carbohydrate moieties.

The combined effects of genotypes and environmental factors together on phenotypic characteristics.

An infant during the first month after birth.

'Abnormalities, Multiple' is a broad term referring to the presence of two or more structural or functional anomalies in an individual, which may be genetic or environmental in origin, and can affect various systems and organs of the body.

Selective abortion of one or more embryos or fetuses in a multiple gestation pregnancy. The usual goal is to improve the outcome for the remaining embryos or fetuses.

Theoretical representations that simulate the behavior or activity of genetic processes or phenomena. They include the use of mathematical equations, computers, and other electronic equipment.

The experimental study of the relationship between the genotype of an organism and its behavior. The scope includes the effects of genes on simple sensory processes to complex organization of the nervous system.

The mass or quantity of heaviness of an individual at BIRTH. It is expressed by units of pounds or kilograms.