Simple Mendelian Genetics in Drosophila Lab objectives: The common fruit fly is a model organism for genetic studies. The reason it is so widely used is because it is easily cultured in the lab, has a short generation time, and can produce many offspring. Before you begin the lab today, you should learn a little about the life cycle of fruit flies.
Vascular plants show a variety of sexual arrangements.
Dioecious species are the ones showing animal-like sexual dimorphismwith female plants bearing flowers containing only ovaries and male plants bearing flowers containing only anthers Figure Some, but not all, dioecious plants have a nonidentical pair of chromosomes associated with and almost certainly determining the sex of the plant.
Of the species with nonidentical sex chromosomes, a large proportion have an XY system. For example, the dioecious plant Melandrium album has 22 chromosomes per cell: Other dioecious plants have no visibly different pair of chromosomes; they may still have sex chromosomes but not visibly distinguishable types.
Figure Two dioecious plant species: Part a, Leslie Bohm; part b, Anthony Griffiths. Cytogeneticists have divided the X and Y chromosomes of some species into homologous and nonhomologous regions. The latter are called differential regions Figure These differential regions contain genes that have no counterparts on the other sex chromosome.
Genes in the differential region of the X show an inheritance pattern called X linkage ; those in the differential region of the Y show Y linkage. Genes in the homologous region show what might be called X-and-Y linkage.
In general, genes on sex chromosomes are said to show sex linkage. Figure Differential and pairing regions of sex chromosomes of humans and of the plant Melandrium album. The regions were located by observing where the chromosomes paired up in meiosis and where they did not.
The genes on the differential regions of the sex chromosomes show patterns of inheritance related to sex. However, crosses following the inheritance of genes on the sex chromosomes often show male and female progeny with different phenotypic ratios.
In fact, for studies of genes of unknown chromosomal location, this pattern is a diagnostic of location on the sex chromosomes. The wild-type eye color of Drosophila is dull red, but pure lines with white eyes are available Figure This phenotypic difference is determined by two alleles of a gene located on the differential region of the X chromosome.
When white-eyed males are crossed with red-eyed females, all the F 1 progeny have red eyes, showing that the allele for white is recessive.
Crossing the red-eyed F1 males and females produces a 3: This inheritance pattern is explained by the alleles being located on the differential region of the X chromosome; in other words, by X- linkage.After observing the white-eye inheritance pattern, Morgan hypothesized that a factor, or gene, controlling eye color was located on the X chromosome.
Female flies have two X chromosomes, and males have one X chromosome and one Y chromosome. Mode of Inheritance for Eye Color in Drosophila Melanogaster Week 3 2 genes involved with eye color White-eyes is a sex-linked trait Wild-type, scarlet, and brown eyes are autosomal traits Comparative Research Crossing wild-type with brown-eyed Drosophila (Hunt ).
Sex-linked genes are located on one of the sex chromosomes (usually the X chromosome).
Thus, the genotypic notation for a mutant gene for white eye color on the X chromosome would look like: X w X w = white-eyed female. Inheritance Patterns in Monohybrid and Dihybrid Crosses for sepia eye color and apterous (wingless) Mutations in Drosophila melanogaster Spencer Wiles and Kristian M.
Hargadon Department of Biology, Hampden-Sydney College, Hampden-Sydney, VA Sex linkage is a form of alternative inheritance pattern where by a specific gene is found on (X or Y chromosomes) sex chromosomes.
Sex linked traits occur mainly in males since they only have one X-chromosome but in females they occur only when they are homozygous recessive (Roberts ). In Drosophila melanogaster there is a sex linked gene for eye color that is found only on the X chromosome.
The allele for red eye color (Xw+) is dominant over the allele for white eye color (Xw). You examine a vial of flies that are all offspring from a single genetic cross.