and a normal chromosome together, giving unbalanced gametes with duplications and deficiencies leading to non-viable zygotes. Adjacent segregation is of two kinds depending on whether non-homologous (adjacent-1)or homologous (adjacent-2) centromeres segregate together. Adiacent-l segregation is the usual type of adjacent gregation, adjacent-2 segregation is rare adjacent-l segregation segregation of non-homologous centromeres during meiosis in a reciprocal translocation heterozygote such that unbalanced gametes with duplications and deficiencies are produced. See alternate segregation and adiacent-2 segregation adjacent-2 segregation segregation of homologous centromeres during meiosis in a translocation heterozygote such that unbalanced gametes with duplications and deficiencies are produced. See alternate segregation and adiacent-I segregation ADP Adenosine diphosphate affected Individuals in a pedigree that exhibit the specific phenotype under study Ala Alanine(an amino acid) albino a pigmentless white phenotype, determined by a mutation in a gene coding for a pigment-synthesizing enzyme alkylating agent A chemical agent that can add alkyl groups(for example, ethyl or methyl groups)to another molecule; many mutagens act through alkylation allele Alternative form of a gene. One of the different forms of a gene that can exist at a single allele frequency Often called gene frequency. A measure of how common an allele is in a population; the proportion of all alleles at one gene locus that are of one specific type in a population allelic exclusion a process whereby only one immunoglobulin light chain and one heavy chain gene are transcribed in any one cell; the other genes are repressedand a normal chromosome together, giving unbalanced gametes with duplications and deficiencies leading to non-viable zygotes. Adjacent segregation is of two kinds depending on whether non-homologous (adjacent-1) or homologous (adjacent-2) centromeres segregate together. Adjacent-1 segregation is the usual type of adjacent segregation, adjacent-2 segregation is rare. adjacent-1 segregation segregation of non-homologous centromeres during meiosis in a reciprocal translocation heterozygote such that unbalanced gametes with duplications and deficiencies are produced. See alternate segregation and adjacent-2 segregation. adjacent-2 segregation segregation of homologous centromeres during meiosis in a translocation heterozygote such that unbalanced gametes with duplications and deficiencies are produced. See alternate segregation and adjacent-1 segregation. ADP Adenosine diphosphate. affected Individuals in a pedigree that exhibit the specific phenotype under study. Ala Alanine (an amino acid). albino A pigmentless white phenotype, determined by a mutation in a gene coding for a pigment-synthesizing enzyme. alkylating agent A chemical agent that can add alkyl groups (for example, ethyl or methyl groups) to another molecule; many mutagens act through alkylation. allele Alternative form of a gene. One of the different forms of a gene that can exist at a single locus. allele frequency Often called gene frequency. A measure of how common an allele is in a population; the proportion of all alleles at one gene locus that are of one specific type in a population. allelic exclusion A process whereby only one immunoglobulin light chain and one heavy chain gene are transcribed in any one cell; the other genes are repressed