Semakan pada 09:37, 31 Ogos 2012

910

Dalam eugenik¹, disiplin yang mencari jalan untuk meningkat kualiti hidup penduduk, penekanan diberikan kepada peranan keturunan², perpindahan ciri keturunan³, seperti warna mata, dari satu generasi ke generasi lain. Ciri yang diperoleh ⁴ tidak di pindah. Ciri maut⁵ amnya membawa kematian awal janin.

• 1. Eugenik, n. - eugenik, adj. - eugenik, n.: a pakar eugenik.
• 2. keturunan, n. - keturunan, adj.

911

Pemindahan ciri keturunan beroperasi menerusi gen¹ yang diwarisi kepada anak oleh ibu bapa mereka. Genetik²adalah sains berkenaan dengan pewarisan dan kesan faktor keturunan. Gen dibawa oleh [{TextTerm|kromosom|3|911|IndexEntry=kromosom}} adalah filamen panjang DNA (asid deoksiribonukleik) yang terletak dalam nukleus sel. Kedudukan gen pada kromosom dipanggil lokus⁴. Gen yang menduduki lokus4 yang sama mengakibatkan sifat-sifat yang sama, walaupun ia boleh berlaku dalam pelbagai cara yang sesuai dengan pelbagai alel⁵ gen dalam lokus tersebut. Sel baru yang dibentuk oleh penyatuan dua sel seksual atau gamet⁶ semasa proses persenyawaan (602-1) dipanggil zigot⁷.

1. Semua gen yang dibawa oleh individu adalah secara kolektif dikenali sebagai pembawaan genetik 2. Genetik, n. - Genetik, adj. – Ahli Genetik, n: pakar dalam bidang genetik

912

The set of two genes of an individual at the same locus is called a genotype¹; the genotype is said to be homozygous² if the alleles are identical at a given locus; it is said to be heterozygous³ in the opposite case. The phenotype⁴ consists in the observable characteristics as determined by the genotype and the environment. If an heterozygous individual (AA’) cannot be distinguished from an homozygous individual (AA), the allele A is said to be dominant⁵ over allele A’, and A’ is said to be recessive⁶. Genes are subject to sudden and apparently random changes, called mutations⁷. Panmixia⁸ or random mating⁸ insures uniform distribution of genes within populations.

• 7. Mutation, n. - mutant, adj. or n.

913

A distinction is frequently made in eugenic policy between positive eugenics¹, aimed at increasing the number of persons believed to have desirable characteristics, and negative eugenics² aimed at restricting the reproduction of persons expected to transmit undesirable characteristics or hereditary defects³. Much attention has been given to the discussion of eugenic sterilization⁴, i.e., the sterilization of persons likely to transmit undesirable characteristics to their descendants. Objections to this measure have been raised on moral grounds and also because of its relatively low efficiency in reducing the frequency of recessive genes (912-6). Among the measures proposed, pre-marital examination⁵ may be mentioned; this is designed to give couples intending to marry information about the probable quality of their offspring, so that prospective partners to dysgenic marriages⁶, i.e., those likely to produce defectives, may be warned.

914

The probability that an individual of reproductive age will have a given number of offspring who also attain reproductive age may depend on his genotype (912-1). This differential reproduction is called selection¹. The selective value² or fitness value² of a genotype is the relative number of children of individuals with the genotype who survive to reproductive age. The mean selective value³ or fitness³ of a population is equal to the average of the selective values for the genotypes of its members. The genetic load⁴ of the population is the relative decline in the mean value of fitness resulting from the presence of different genotypes with varying fitness values. Random fluctuation of the frequency with which a specific gene is found in different generations of a population is called the genetic drift⁵. The gene structure⁶ of a population refers to the distribution of the frequencies of different alleles (911-5) on a given locus (911-4) within the members of the population. The genotypic structure⁷ of a population refers to the distribution of different genotypes on the same locus.

915

In the case of an inbred individual, i.e., an individual whose parents have a common ancestor, two genes are said to be identical genes¹ by descent, if both were carried by the same ancestor and are on the same locus. The probability that an individual chosen at random in a population carries two genes identical by descent is the coefficient of inbreeding² of the population. The coefficient of kinship³ of a population is the probability that two individuals chosen at random in that population carry genes identical by descent on the same locus.

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