Introduction to Drosophila Genetics
INTRODUCTION TO DROSOPHILA GENETICS
DROSOPHILA CULTURE We will study basic principles of Mendelian inheritance with the use of the fruit fly, Drosophila melanogaster [the name means “black-bodied fruit-lover”]. Drosophila was one of the first organisms to be studied genetically: its small size, short life cycle (10 ~14 days at 25oC), high reproductive rate (an adult female can lay 400-500 eggs in 10 days), and ease of culture and genetic manipulation have made it perhaps the best understood animal genetic system. Many different species, and a large number and wide variety of naturally-occurring and artificially-induced genetic variants are available. The partial genetic map in Appendix B describes the location of all the mutations used in crosses and lab questions. VIRGIN FEMALES All female flies used in controlled genetic crosses must be “virgins”. Female flies are capable of mating as early as 8 hours after emerging from the pupae stage and are polyandrous, that is, capable of mating with several males. Once mated, females can retain viable sperm for several days and this will confuse the results of a subsequent controlled mating. To prevent this, all adult flies are removed from the culture bottle about 7 hours prior to lab time, so that all newly hatched flies will remain virgin. BASIC GENETICS The karyotype of Drosophila comprises four pairs of chromosomes, of which three pairs are autosomes and one pair are sex chromosomes. Female Drosophila are XX, and males XY. A gene is a heritable factor that controls the expression of some trait, which may be morphological, behavioural, molecular, etc. Each such gene occupies a specific physical locus (pl. loci) on a particular chromosome. Variant forms of these loci are termed alleles. Gene, locus, and allele are often used more or less interchangeably, and this can lead to confusion. Gene is the popular and most general term, and is most appropriate when the inherited basis of a trait is emphasized, e.g., a “gene” for
DROSOPHILA CULTURE We will study basic principles of Mendelian inheritance with the use of the fruit fly, Drosophila melanogaster [the name means “black-bodied fruit-lover”]. Drosophila was one of the first organisms to be studied genetically: its small size, short life cycle (10 ~14 days at 25oC), high reproductive rate (an adult female can lay 400-500 eggs in 10 days), and ease of culture and genetic manipulation have made it perhaps the best understood animal genetic system. Many different species, and a large number and wide variety of naturally-occurring and artificially-induced genetic variants are available. The partial genetic map in Appendix B describes the location of all the mutations used in crosses and lab questions. VIRGIN FEMALES All female flies used in controlled genetic crosses must be “virgins”. Female flies are capable of mating as early as 8 hours after emerging from the pupae stage and are polyandrous, that is, capable of mating with several males. Once mated, females can retain viable sperm for several days and this will confuse the results of a subsequent controlled mating. To prevent this, all adult flies are removed from the culture bottle about 7 hours prior to lab time, so that all newly hatched flies will remain virgin. BASIC GENETICS The karyotype of Drosophila comprises four pairs of chromosomes, of which three pairs are autosomes and one pair are sex chromosomes. Female Drosophila are XX, and males XY. A gene is a heritable factor that controls the expression of some trait, which may be morphological, behavioural, molecular, etc. Each such gene occupies a specific physical locus (pl. loci) on a particular chromosome. Variant forms of these loci are termed alleles. Gene, locus, and allele are often used more or less interchangeably, and this can lead to confusion. Gene is the popular and most general term, and is most appropriate when the inherited basis of a trait is emphasized, e.g., a “gene” for