Drosophila Melanogaster

Title

: Genetic Inheritance of Drosophila Melanogaster

Objectives : 1. To determine the genotypes of parental generation of Drosophila melanogaster by observing both the F1 and F2 generations and applying Chi Square analysis to the F2 offspring 2. To understand the principles that governs inheritance of genes on sex chromosomes. 3. To design genetic crosses to illustrate independent assortment and sex-linkage 4. To differentiate between male and female Drosophila melanogaster.

Introduction: A monohybrid cross is a cross between parents who are heterozygous at one locus. Monohybrid inheritance is the inheritance of a single characteristic. The different forms of the characteristic are usually controlled by different alleles of the same gene. For example, a monohybrid cross between two pure-breeding plants (homozygous for their respective traits), one with yellow seeds (the dominant trait) and one with green seeds (the recessive trait), would be expected to produce an F1 (first) generation with only yellow seeds because the allele for yellow seeds is dominant to that of green. A monohybrid cross compares only one trait. In dihybrid cross, in which two characteristics were observed, the F1 generation only expressed the dominant phenotype. In F2 generation, both dominant and recessive traits were expressed and four phenotypic categories with a ratio of 9:3:3:1 were noticed. This cross lead to the Law of Independent Assortment, which states that each pair of alleles segregate independently of other pairs of alleles during gametogenesis. This is sex-linked genes, genes located on one of the sex chromosomes (X or Y) but not the other. Since, typically the X chromosome is longer, it bears a lot of genes not found on the Y chromosome, thus most sex-linked genes are X-linked genes. One example of a sex-linked gene is fruit fly eye color. Drosophilia melanogaster, the fruit fly, is an excellent organism for genetics studies because it has simple food requirements, occupies little space, is hardy, completes its life cycle in about 12 days at room temperature, produces large numbers of offspring, can be immobilized readily for examination and sorting, and has many types of heredity variations that can be

observed with low power magnification. Drosophila has a small number of chromosomes ( four pairs). These chromosomes are easily located in the large salivary gland cells. To ensure a controlled mating, it is necessary to use females that have not been mated before (virgins).

Methodology: Materials: 1. Dissecting microscope 2. Petri dish 3. Sterile plastic vials with foam cover 4. Fine-bristle paintbrushes 5. Anesthetic 6. Fruit fly nutrition compound

Method: 1. A vial of wild type flies was obtained. These flies were immobilizing and sexing. These flies were examined and the characteristics were noted. 2. The immobilized flies were placed on petri dish . the flies were placed under the dissecting microscope to view the characteristics. 3. Male flies were distinguished from female flies. 4. There were 4 types of Drosophila that need to be done are:

Types of Crossing

MALE

FEMALE

Monohybrid

Ebony body

Black body

Dihybrid

Black body, red eyes

Ebony body, white eyes

X-linked

White eyes

Red eyes

Red eyes

White eyes

5. 5 males and 5 females of Drosophila for each cross were choosing. 6. Each vial have 5 pairs of experimental flies. The cross number of vial have been recorded. The female laid eggs on the surface of culture medium. The eggs represent the first filial, F1 generation and will be emerging from their pupal cases in about a week. 7. The parental flies were immobilized and removed. 8. At second week, the F1 generation was begin be observed. The characteristic and sex of the flies were recorded. 9. Five pairs of F1 flies were placed in fresh culture vial to produce F2 generation. For this cross the females need not be virgins. 10. After the F2 eggs had been hatched, the F1 generation were immobilized and removed from the vial. 11.The F2 flies were begin removed. Their sex and the presence or absence of mutation were observed. The more F2 flies collected, the more reliable the data will be

A. Mohohybrid cross

Result: Table 1: Phenotypes of F1 generation Number of progeny Phenotype

Males

Females

Total

Black body

43

56

99

Ebony body

0

0

0

Table 2: Phenotypes of F2 generation Number of progeny Phenotype

Males

Females

Total

Black body

40

46

86

Ebony body

13

11

24 110

Class

Observed

Expected

(O-E)2

(O-E)2/Expected

Black body

86

82.5

12.25

0.148

Ebony body

24

27.5

12.25

0.445

Totals

110

110

Chi2 = 0.593 Df = 1, 0.5>p>0.1

Discussion: Monohybrid cross breeding refer to a genetic cross between parents that differ in the alleles they posses for one particular gene, one parent having two dominant alleles and the other two recessives. All of the offspring (called monohybrids) have one dominant and one recessive allele for that gene. Crossing between these offspring yields a characteristic 3:1 ratio in the following generation of dominant:recessive phenotypes.

In crossbreeding between Drosophila melanogaster black body male with ebony body female, the F1 generations yields are all black body,43 males and 56 females. All offsprings are shown black body because black alleles are dominant to ebony alleles. The dominant alleles shows in phenotype appearance. We take the F1 generation and do the self-breeding. In F2 generation, the offsprings yields are 40 black body males, 46 black body females, 13 ebony males and 11 ebony females. The ebony appearance shows in F2 generation because the it is recessive alleles. The number of ebony is one over 16 from the total number of offspring. After calculated the value of chi, we determined that the number of offspring yields observed are nearly same with the expected offspring. Df is 1, 0.5>p>0.1.

B. Dihybrid cross Result: Class

Observed

Black body, red 45

Expected

(O-E)2

(O-E)2/Expected

43.9

1.21

0.028

eyes Black

body, 13

14.6

2.56

0.175

body, 16

14.6

1.96

0.134

body, 4

4.9

0.81

0.165

white eyes Ebony red eyes Ebony white eyes Totals

78

78

Chi2 = 0.502 Df = 3, 0.5>p>0.1

Discussion: Dihybrid cross involved 2 traits of Drosophila which were between colour of body and eye colour has been crossed in this experiment. We know that the gene that controls these traits is autosomal chromosomes. Since the autosomal chromosomes control these traits, the cross can be done by using normal cross without x- link. The Chi Square test is a statiscal method used to determine goodness of fit. Goodness of fit refers to how close the observed data are to those predicted from a hypothesis. The chi square test does not prove that the hypothesis is correct, it evaluates whether or the data and the hypothesis have good fit. In this case, we have used the chi square test. So we have to determine the degrees of freedom (df). The df is a measure of the number of categories that are independent of each other. Based on the result that has been calculated, therefore, with df= 3, the chi square value of 0.502 is greater than 0.352 in which correspond to P= 0.95. Low chi square of the calculated result indicates a high probability that the observed deviations could be due to random chance alone. P= 0.95 means that values equal or greater than 0.352 are expected to occur 95% of the time based on random chance alone. Therefore, it is quite probable that the deviations between the observed and expected values in this experiment can be explained by random sampling error. The calculated result that we obtained can be accepted because it is greater than 0.05.

C. X-linked gene cross Result:

Cross 1 Female wild type (red eye) X Male white eye phenotype

Number of flies

Male wild type

27

Female wild type

24

Male white eye

31

Female white eye

20

Cross 2 Male wild type (red eye) X Female white eye phenotype

Number of flies

Male wild type

23

Female wild type

17

Male white eye

18

Female white eye

16

Discussion: T.H. Morgan in 1910 crossed a red eyed pure breeding female fly with a white eyed male. For cross 1:

Red eyed female X White eyed male.

For this cross, the F1 generation yield all red eyed offsprings. When the F1 is inbred, white eye appears in ¼ th of the F2 generations as in Mendel’s monohybrid experiment. For autosomal gene, F2 offspring all the females are red. But among the males, half are white eyed. This occupies ratio 3 red eyes : 1 white eyes.

The parent red eyed female must be homozygous, XW+XW+ and white eyed male must be XwY. thus, red eyed female transmit their red eyed gene to all their

F1 offspring through X

chromosomes. So F1 offspring are red eyed. For cross 2 : Red eyed male X white eyed female For this reciprocal cross, the F1 generation yield all females are red eyed while all the male are white eyed. They are produced in equal number. When these F1 offspring are interbred, F2 offsprings consist of red and white eyed individuals in equal proportion in both the sexes.the ration yield is 1 red : 1 white. The parent red eyed male must be hemizygous,XW+Y and white eyed female must be XwXw. The Xw are fertilized by XW+ and Y. So it yield XW+Xw and XwY . The F1 generation would be heterozygous and hemizygous recessive. Based on our experiment, for cross 1 we cannot get F2 generation with ratio 1 red male : 2 red female : 1 white male. Probably this happened because of the error in counting F2 generation. During the disposing of F1 generation, there are a few egg of F1 are not hachted yet. So we assume that the egg are F2 generation. Other than that, probably we have did some error in distinguished male and female drosophila.

Conclusion: The number of offspring yields in F1 and F2 generation are following Mendel’s ratio. Based on this experiment, we can conclude that the dihybrid cross in Drosophila is succeed although we have to repeat it twice due to some errors. In x-linked cross, a red eye is the dominant trait towards white eyes. In F2 generation, white eyes only affected male Drosophila. The ratio of the F2 phenotype ratio is 3:1.The gene affected in the white-eye mutant is located exclusively on the X chromosome.

References: N.A Campbell & J.B Reece (2005). Biolology 7th ed., San Fransisco.

Pearson Benjamin

Cummings. http://biology.clc.uc.edu/Courses/bio105/sex-link.htm http://main.uab.edu/cord/show.asp?durki=45462 http://en.wikipedia.org/wiki/Drosophila_melanogaster http://www.studentsguide.in/genetics/sex-linked-inheritance/html http://www.microbiologyprocedure.com/genetics.html

UNIVERSITI PENDIDIKAN SULTAN IDRIS

TBG 2013

Mendelian Inheritance Patterns in Drosophila Melanogaster

NAME LEE TACK HOOI MUHAMMAD SHAKIR BIN CHE SOH

MATRIC NO D20081032349 D20081032384

D20081032384 WAN MOHD SYAHIRAN BIN WAN SABARUDIN

D20081032317

NURUL AIN FATHIHAH BT MOHD ROSHIDAN

D20081032381

RAJA NUR AIMI BT RAJA IBRAHIM

D20081032328

LECTURER’S NAME : DR FATIMAH BT MOHAMED GROUP : A SEMESTER 3