Mendel's law

Men·del's law   (měn'dlz)    n.   One of two principles of heredity first formulated by Gregor Mendel, founded on his experiments with pea plants and stating that the members of a pair of homologous chromosomes segregate during meiosis and are distributed to different gametes. Also called law of segregation. The second of these two principles, stating that each member of a pair of homologous chromosomes segregates during meiosis independently of the members of other pairs, so that alleles carried on different chromosomes are distributed randomly to the gametes. Also called law of independent assortment.

Mendel\'s law

Men"del's law\ A principle governing the inheritance of many characters in animals and plants, discovered by Gregor J. Mendel (Austrian Augustinian abbot, 1822-84) in breeding experiments with peas. He showed that the height, color, and other characters depend on the presence of determinating factors behaving as units. In any given germ cell each of these is either present or absent.

Note: The following example (using letters as symbols of the determining factors and hence also of the individuals possessing them) shows the operation of the law: Tallness being due to a factor T, a tall plant, arising by the union in fertilization of two germ cells both bearing this factor, is TT; a dwarf, being without T, is tt. Crossing these, crossbreeds, Tt, result (called generation F_1). In the formation of the germ cells of these crossbreeds a process of segregation occurs such that germ cells, whether male or female, are produced of two kinds, T and t, in equal numbers. The T cells bear the factor "tallness," the t cells are devoid of it. The offspring, generation F_2, which arise from the chance union of these germ cells in pairs, according to the law of probability, are therefore on an average in the following proportions: 1 TT : 2 Tt : 1 tt; and thus plants pure in tallness (TT) and dwarfness (tt), as well as crossbreeds (Tt), are formed by the interbreeding of crossbreeds. Frequently, as in this example, owning to what is called the dominance of a factor, the operation of Mendel's law may be complicated by the fact that when a dominant factor (as T) occurs with its allelomorph (as t), called recessive, in the crossbreed Tt, the individual Tt is itself indistinguishable from the pure form TT. Generation F_1, containing only the Tt form, consists entirely of dominants (tall plants) and generation F_2 consists of three dominants (2 Tt, 1 TT) to one dwarf (tt), which, displaying the feature suppressed in F_1, is called recessive. Such qualitative and numerical regularity has been proved to exist in regard to very diverse qualities or characters which compose living things, both wild and domesticated, such as colors of flowers, of hair or eyes, patterns, structure, chemical composition, and power of resisting certain diseases. The diversity of forms produced in crossbreeding by horticulturists and fanciers generally results from a process of analytical variation or recombination of the factors composing the parental types. Purity of type consequently acquires a specific meaning. An individual is pure in respect of a given character when it results from the union of two sexual cells both bearing that character, or both without it.

Main Entry: Men·del's law
Pronunciation: "men-d^&lz-
Function: noun
1 : a principle in genetics: hereditary units occur in pairsthat separate during gamete formation so that every gamete receives but one member of a pair called also law of segregation
2 : a principle in genetics limited and modifiedby the subsequent discovery of the phenomenon of linkage: the different pairs of hereditary units are distributed to the gametes independently of each other, the gametes combine at random, and thevarious combinations of hereditary pairs occur in the zygotes according to the laws of chance called also law of independent assortment
3 : a principle in genetics provedsubsequently to be subject to many limitations: because one of each pair of hereditary units dominates the other in expression, characters are inherited as alternatives on an all-or-nothing basiscalled also law of dominance

Mendel's law Men·del's law (měn'dlz)
n.

1. One of two principles of heredity first formulated by Gregor Mendel, founded on his experiments with pea plants and stating that the members of a pair of homologous chromosomes segregate during meiosis and are distributed to different gametes. Also called law of segregation.
2. The second of these two principles, stating that each member of a pair of homologous chromosomes segregates during meiosis independently of the members of other pairs, so that alleles carried on different chromosomes are distributed randomly to the gametes. Also called law of independent assortment.

Mendel's law   (měn'dlz)  Pronunciation Key  Any of the principles first proposed by Gregor Mendel to describe the inheritance of traits passed from one generation to the next. ◇ Mendel's first law (also called the law of segregation) states that during the formation of reproductive cells (gametes), pairs of hereditary factors (genes) for a specific trait separate so that offspring receive one factor from each parent. ◇ Mendel's second law (also called the law of independent assortment) states that chance determines which factor for a particular trait is inherited. ◇ Mendel's third law (also called the law of dominance) states that one of the factors for a pair of inherited traits will be dominant and the other recessive, unless both factors are recessive. See more at inheritance.