Before you begin the lab today, you should learn a little about the life cycle of fruit flies. The white-eyed fruit fly gene is recessive and typically is eliminated after mating with dominant-eyed fruit flies for two generations. Such type of inheritance is also called as criss-cross inheritance. The ratio of wild type to sepia to vestigial and to sepia, vestigial of 9. Obtain a piece of filter paper 15 cm x 23 cm and, with a pencil, lightly draw a line 1. Females in a tubular receptacle and in two mushroom-shaped ; sperm from multiple matings compete for fertilization.
It is also simple to find out to which chromosome the P-element has inserted itself on by performing crosses and watching where the eye colour goes. The females were all red eyed whereas 50% males were white eyed and the remaining 50% males were red eyed Fig. Quickly, the bottle is separated from its cover. Under normal diploid conditions a female fruit fly has two X chromosomes, a male has an X and a Y chromosome. Sensory neurons in the uterus of female D. Decide on the mode of inheritance of each phenotype i.
The same was done for ebony females with wild type males. Introduction: Gregor Mendel was born in 1822, is now known as Father of Genetics. Etherize your parental flies for 2-3 min. Proc Natl Acad Sci U S A. This decreased mating latency leads to a greater mating efficiency for experienced males over naïve males. The genes for white eyes colorless eyes and bar eyes small eyes are both found on chromosome 1 of drosophila melanogaster Russell, 1994.
Procedures for dihybrid crosses 1. Archived from on 8 October 2011. Simple Mendelian Genetics in Drosophila Simple Mendelian Genetics in Drosophila Lab objectives : 1 To familiarize you with an important research organism, the fruit fly, Drosophila melanogaster. Leave the vial on its side until the flies revive. The phenotypes of the progeny are shown below. The eye color is what distinguished it as being different than the wild type.
It took nearly two weeks for adult flies in the F1 to emerge in the colder environment. Sexing via the sex comb can also be done successfully in the pupal stage Hadden and Cunningham, 1970. In fact, for studies of genes of unknown chromosomal location, this pattern is a diagnostic of location on the sex chromosomes. The pea plant was perfect organism for Mendel to observe because it reproduces quickly, and in large numbers, and is fairly easy to manipulate. Let's start by asking the simple question: is the white 1 allele inherited as a simple recessive? Cytogeneticists have divided the X and Y chromosomes of some into homologous and nonhomologous regions.
In some species, a warm nest produces all females, and a cold nest produces all males. One mechanism, autosomal inheritance, involves the passing of a gene found on an X chromosome coded for by two alleles. Distinguishing characteristics of male and female Drosophila. Each photoreceptor cell consists of two main sections, the cell body and the. If both flies are homozygous, how would you denote the cross described? The reciprocal gives a different result. Chicago: University of Chicago Press. Although this ratio is close to the expected 9:3:3:1 ratio for a dihybrid cross, the Chi square test performed to determine whether this experimental data differed significantly from the 9:3:3:1 ratio expected for simple dihybrid cross.
Drosophila is widely used for education because it is a fantastic model organism. Those are the only two inheritance mechanisms that involve the X chromosome. The Test-cross or back-cross : To test prediction 2, we must perform the following cross: If we draw this out in a Punnett Square, we obtain this: Only in the top row of the table do we find the bw + allele, so only the flies represented in this row will have red eyes. If you crossed a homozygous ebony body male with a homozygous apterous wing female, what would the F2 genotypic and phenotypic ratios be assuming you produced the F2 by crossing two of the F1 flies together? The males have a sex comb of about 10 black bristles on the forelegs; females do not have a sex comb. Chi-squared was greater than this value, so that meant the proposed ratio had to be rejected. In this case, the differences seen are probably due to the small sample size scored from the cross. X5 had a chi square value of 12.
In order to accomplish this, a reciprocal cross was performed by mating wild type male flies with mutant female flies and then wild type female flies with mutant male flies. The Punnett square predicted ¼ wild type females, ¼ wild type males, ¼ mutant D females, and ¼ mutant D males. The rest is killed and the traits are observed. Soon after, the male positions himself at the rear of the female's abdomen in a low posture to tap and lick the female genitalia. In the offspring, all the daughters are red eyed heterozygotes Rr and all sons are red eyed homozygotes R-.
Parental cross P female P male b. Therefore, in determining the mode of inheritance of a genetic trait, it is important to distinguish the sex of the flies and to record the number of flies of each sex in each phenotype. Other dioecious plants have no visibly different pair of chromosomes; they may still have sex chromosomes but not visibly distinguishable types. They are as follows: i The genes which are located on X-chromosomes are called X-linked genes or sex linked genes. Again, we can understand this by thinking about the mechanism by which the genotype gives rise to the phenotype. Phenotypes Number of progeny Males Females Total Wild type 27 38 65 Scarlet eyes 7 12 19 84 To determine the statistical relevance of the data, we performed the Chi square test on our F2 data. Once a number of vials were set up and breeding well, we began to separate out virgin females from both the wild type and the ebony Drosophila.
This section needs additional citations for. Chi-squared was less than this value, so that meant the proposed ratio could not be rejected. While we may be able to choose the parents for each cross, and establish homogeneous lineages for our studies, the studies are very slow. Drosophila as a Model System Why Model Systems are Necessary When we first examined , we found that it is difficult to unravel the rules of genetic inheritance when studying a species that has only a few offspring in each generation. The same P-element containing a white gene capable of producing a red colour could produce anything on the white-red spectrum depending on where it lands.