AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

ClB technique – Drosophila

CIB TECHNIQUE - DROSOPHILA

Attached X chromosome method detecting sex-linked visible mutation

• In this method females with attached X-chromosomes are used.
• Attached X - chromosomes undergo compulsory non-disjunction (failure of homologous chromosome to separate during anaphase) since the two X - chromosomes are joined to a single centromere.
• The mutagen treated males are crossed with XXY females.
• In this case if any mutation with visible effect has occurred, that will be expressed in all the viable the male progeny.
• In such attached-X mating, the male progeny receive their X chromosome from their male parent rather than from their female parent as in a normal mating.
• If the male parent is treated with a mutagenic agent such as X - rays, the increased frequency of recessive visible mutations can be easily assessed by screening the male progeny of attached-X mating.
• X rays and most other forms of ionising radiation are quantified in roentgen units (r units), which are measured in terms of the number of ionizations per unit volume under a standard set of conditions.
• More specifically one r unit is the quantity of ionising radiations that produces one electrostatic unit of charge in a 1 - cm³ volume.
• The same dosage of irradiation may be obtained by a low intensity of irradiation over a long period of time or high intensity of irradiation for a short period of time.
• This is important because in most studies the frequency of induced point mutations is directly proportional to the dosage of irradiation.