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  Section: Biotechnology Methods » Cell Biology and Genetics
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Demonstration of the Law of Independent Assortment

Cell Biology and Genetics
  Cell Cycles
  Meiosis in Flower Buds of Allium Cepa-Acetocarmine Stain
  Meiosis in Grasshopper Testis (Poecilocerus Pictus)
  Mitosis in Onion Root Tip (Allium Cepa)
  Differential Staining of Blood
  Buccal Epithelial Smear and Barr Body
  Vital Staining of DNA and RNA in Paramecium
  Induction of Polyploidy
  Mounting of Genitalia in Drosophila Melanogaster
  Mounting of Genitalia in the Silk Moth Bombyx Mori
  Mounting of the Sex Comb in Drosophila Melanogaster
  Mounting of the Mouth Parts of the Mosquito
  Normal Human Karyotyping
  Black and White Film Development and Printing for Karyotype Analysis
  Study of Drumsticks in the Neutrophils of Females
  Study of the Malaria Parasite
  Vital Staining of DNA and RNA in Paramecium
  Sex-Linked Inheritance in Drosophila Melanogaster
  Preparation of Somatic Chromosomes from Rat Bone Marrow
  Chromosomal Aberrations
  Study of Phenocopy
  Study of Mendelian Traits
  Estimation of Number of Erythrocytes [RBC] in Human Blood
  Estimation of Number of Leucocytes (WBC) in Human Blood
  Culturing Techniques and Handling of Flies
  Life Cycle of the Mosquito (Culex Pipiens)
  Life Cycle of the Silkworm (Bombyx Mori)
  Vital Staining of Earthworm Ovary
  Culturing and Observation of Paramecium
  Culturing and Staining of E.coli (Gram’s Staining)
  Breeding Experiments in Drosophila Melanogaster
  Preparation of Salivary Gland Chromosomes
  Observation of Mutants in Drosophila Melanogaster
  ABO Blood Grouping and Rh Factor in Humans
  Determination of Blood Group and Rh Factor
  Demonstration of the Law of Independent Assortment
  Demonstration of Law of Segregation

Mendel’s second law is known as the law of independent assortment, which states that 2 different sets of genes assort independently of each other during the formation of gametes through meiosis. The cross conducted taking 2 contrasting pairs of characteristics is known as the dihybrid cross and it produces 9:3:3:1 in the F2 generation. In Drosophila, this was stated by Morgan. In this experiment, pairs of contrasting characters, such as sepia-eye and vestigial-eye mutants were taken to study whether inheritance patterns follow the Mendelian laws or not. Vestigial wing is characterized by reduced wings and balancers and the sepia-eye mutant is characterized by brown eyes.

  • Drosophila melanogaster
  • Sepia vestigial mutant
  • Media bottles
  • Anaesthetic ether
  • Etherizer
Normal D. melanogaster strain and sepia vestigial wing strains were taken in standard media bottles separately. When the flies were ready to emerge from the pupa, the original stock were discarded. The newly emerged male and female virgins were isolated. Flies that were collected were aged for 3–5 days, and were crossed with each other by conducting a reciprocal cross also. The 2 crosses also occurred in the following 2 manners.

Normal females × sepia vestigial males.
Normal males × sepia vestigial females.

The progeny produced in F1 were observed for phenotypic expression and the data were collected and recorded. By taking a few of the F1 flies, inbreeding was carried out to obtain F2 generation. The phenotype of F2 flies were observed and the data were recorded.

Direct Cross
Parents: sepia vestigial females × normal males
F1: all were normal-eyed and normal-winged
Inbreed: F1 females × F1 males
F2 : normal-winged vestigial-winged normal-winged vestigial-winged
And red-eyed : and red-eyed : and sepia-eyed: and sepia-eyed
Ratio: 177 : 60 : 65 : 20
Phenotype Observed Expected Deviation d2 d2/E
Normal-winged 177 181.12 – 4.12 16.97 0.07
And red-eyed
Vestigial-winged 60 60.37 – 0.37 0.137 0.002
And red-eyed
Normal-winged 65 60.37 + 4.63 21.43 0.35
And sepia-eyed
Vestigial-winged 20 20.12 – 0.12 0.0144 0.0007
And sepia-eyed
Degree of freedom = 4 – 1 = 3
Sx2 = 0.4427

Reciprocal Cross
Parents: normal females × sepia vestigial males
F1: all were normal-eyed (red) and normal-winged.
Inbreed: F1 female × F1 male
F2: red-eyed and normal-winged: red-eyed vestigial-winged: sepia-eyed and
normal-winged: sepia-eyed and vestigial-winged
Ratio: 212:70:66:22
Phenotype Observed Expected Deviation d2 d2/E = X2
Red-eyed and 212 208.12 3.88 15.05 0.0723 normal-winged
Red-eyed and 70 69.71 0.625 0.390 0.0055
Sepia-eyed and 66 69.375 3.375 11.396 0.164
Sepia-eyed and 22 23.12 1.125 1.265 0.0547
Sx2 = 0.029689
Degree of freedom = 4 – 1 = 3 analysis of result.
At the 5% level of significance, at 3 degrees of freedom, table value = 7.815
and at 2, degree of freedom is 5.991.
At the 4 degree of freedom, it is 9.48.
In direct cross, the X2 value = 0.4427 and is less than deviation. In reciprocal
cross, the X2 value = 0.29689 and is less than table value.
In both cases, the deviation is not significant, so the null hypothesis is


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