tailieunhanh - A Dictionary of Genetics phần 6

Tham khảo tài liệu 'a dictionary of genetics phần 6', ngoại ngữ, ngữ pháp tiếng anh phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 288 multifactorial tants replace healthy genes the good ones never come back and so the process resembles a ratchet wheel which moves in only one direction. Muller proposed that sexuality arose because it allowed crossing over to occur between homologous chromosomes from parents carrying different mutants. Recombinant offspring with mutant-free genomes could thus arise and halt the action of the rachet. The term Muller ratchet was coined by J. Felsenstein in 1974. multifactorial polygenic. multiforked chromosome a bacterial chromosome containing more than one replication fork due to the initiation of a second fork before completion of the first replication cycle. multigene family a set of genes descended by duplication and variation from some ancestral gene. Such genes may be clustered together on the same chromosome or dispersed on different chromosomes. Examples of multigene families include those that encode the histones hemoglobins immunoglobulins histocompatibility antigens actins tubulins keratins collagens heat shock proteins salivary glue proteins chorion proteins cuticle proteins yolk proteins and phaseolins. See isoforms reiterated genes. multimer a protein molecule made up of two or more polypeptide chains each referred to as a monomer. The terms dimer trimer tetramer pentamer etc. are used if the number of monomers per multimer is known. Compare with monomer oligomer polymer. multiparous bearing or producing more than one offspring at a birth. See parity. multiple allelism See allele. multiple choice mating referring to an experimental design in studies of behavior genetics where a test organism is allowed to choose between two or more genetically different mates. multiple codon recognition See wobble hypothesis. multiple-event cu rve a curve relating relative survival to radiation dose that contains an initial flat portion. This finding indicates that there is little biological effect until a certain dose has accumulated and suggests that the sensitive