endonuclease that initiates excision repair at apurinic and apyrimidinic sites on dnA AP site Apurinic or apyrimidinic site resulting from the loss of a purine or pyrimidine residue from the dna Arg nine(al ascospore A sexual spore from certain fungus species in which spores are found in a sac called an ascus. Haploid spores found in the asci of Ascomycete fungi ascus In fungi, a sac that encloses a tetrad or an octad of ascospores. The sac in Ascomycete fungi that holds the ascospores asexual spore Sn Asparagine(an amino acid) Aspartate(an amino acid) assignment test a test that determines whether a locus is on a specific human chromosome by observation of the concordance of the locus and the specific chromosome in a panel of human-mouse hybrid cell lines containing only one or a few of the normal set(22 autosomes, X and Y of human chromosomes assortative mating The mating of individuals with similar phenotypes ataxia-telangiectasia a disease(loss of muscle control, and reddening of the skin) in human beings caused by a defect in DNA repair mechanisms induced by ionising radiation(X-rays, beta and alpha particles, gamma rays) ATP (adenosine triphosphate) The energy molecule of cells, synthesized mainly in mitochondria and chloroplasts; energy from the breakdown of ATP drives many importantendonuclease that initiates excision repair at apurinic and apyrimidinic sites on DNA. AP site Apurinic or apyrimidinic site resulting from the loss of a purine or pyrimidine residue from the DNA. Arg Arginine (an amino acid). ascospore A sexual spore from certain fungus species in which spores are found in a sac called an ascus. Haploid spores found in the asci of Ascomycete fungi. ascus In fungi, a sac that encloses a tetrad or an octad of ascospores. The sac in Ascomycete fungi that holds the ascospores. asexual spore See spore. Asn Asparagine (an amino acid). Asp Aspartate (an amino acid). assignment test A test that determines whether a locus is on a specific human chromosome by observation of the concordance of the locus and the specific chromosome in a panel of human-mouse hybrid cell lines containing only one or a few of the normal set (22 autosomes, X and Y) of human chromosomes. assortative mating The mating of individuals with similar phenotypes. ataxia-telangiectasia A disease (loss of muscle control, and reddening of the skin) in human beings caused by a defect in DNA repair mechanisms induced by ionising radiation (X-rays, beta and alpha particles, gamma rays). ATP (adenosine triphosphate) The energy molecule of cells, synthesized mainly in mitochondria and chloroplasts; energy from the breakdown of ATP drives many important reactions in the cell