Farmers used the technique of crossing over for centuries, in order to get the best yeasts, crops e.t.c, but Mendel was the first person who did real genetic study in scientific way
Apparatus
- Culture medium
- Growth medium
- Plastic tube with sponge bung,
- Small plastic ladder
- Yeast
- Water
- Piece of paper/towel
- Microscope
- Black wand
- Flynap
-
Method
- Pour 2mm of growth medium into plastic container.
- Add 10ml of water to dampen the medium
- The medium will turn blue and then add 1 pinch of yeast by sprinkling it on the top.
- Place a small plastic ladder in the container
- leave a minimum of 1 minute
- place culture of drosophila on a piece of paper on a bench, loosen sponge bung
- Take tube of newly prepared medium. Carefully remove both bungs and place new tube on a top of old culture
- Flies travel upward and will enter the container rapidly
- When sufficient flies have entered new tube/container, quickly place it onto paper and bung old culture to stop flies escaping
- Label each tube and note date
- Examine flies regularly
Using a flynap
- In order to count the flies in the tube/pot
- Take a black wand and place into flynap solution with care
- Remove directly and place wand into the pot/tube with the drosophila
- To lightly anaesthetic flies leave wand in the pot/tube for at least 30 seconds.
- Observe the flies and make sure they are not moving
- Then place the flies on a microscope
- Then count the flies by differentiating male from female
- After counting them, place the flies back into the pot/tube
- And put 6 male wild flies with 6 vestigal female flies and in different pot/tube put 6 wild female flies with 6 vestigal males.
- label each tube and write down the date
- And finally examine the flies regularly.
Health and safety
- Flynap could be quick dangerous if misused because it could anaesthetise students if exposed to surroundings, so don’t sniff or taste the flynap.
- Medium used in the experiment could also be harmful
- Wear gloves and lab coat
- Wash hands thoroughly before the lesson, by using a warm water and disinfectant soap and dry them
Results
Observed result (cross 1)
Cross 1 wild male × vestigial female
F1 100% wild 14 male: 14 female
Expected result
XX= female
Xy = male
BB = wild
Bb = vestigal
Cross 1
Parent wild male × vestigial female
Genotype XYBB XXBB
Gametes XB XB YB YB Xb Xb Xb Xb
F1 generation
Male Gametes
Phenotype = 100% wild 8 female : 8 male
Observed result (cross 2)
Cross 2 wild female × vestigial male
F1 100% wild 18 male: 18 female
Expected result
XX = female
XY = male
BB = wild
Bb = wild
bb = vestigial
Cross 2
Parent wild female × vestigial male
Genotype XXBB XYbb
Gametes XB XB XB XB Xb Xb Yb Yb
F1 generation
Male gametes
Phenotype = 100% wild 8 male: 8 female
Observed result (cross 3)
Cross 3 F1 self cross from cross 1
Wild male × vestigial female
F 2 18 wild 9 male : 9 female
6 vestigial 3 male : 3 female
Observed ratio = 3:1
Expected results
XX = female
XY = male
BB = wild
Bb = wild
bb = vestigial
Cross 3
Parent wild female × wild male
Genotype XXBb XYBb
Gametes XB Xb XB Xb XB Xb YB Yb
F1 generation
Male gametes
Female
Gametes
Phenotype = 75% wild 6 female: 6 male
25% vestigial 2 female: 2 male
Expected ratio = 3:1
Observed result (cross 4)
Cross 4 F1 self cross from cross 2
Wild male × wild female
F2 24 wild 12 male: 12 female
8 vestigial 4 male: 4 female
Observed = 3:1
Expected result
XX = female
XY = male
BB = wild
Bb= wild
bb= vestigial
Cross 4
Parent wild female × wild male
Genotype XXBb XYBb
Gamete XB Xb XB Xb XB Xb YB Yb
F1 generation
Male gametes
Female
Gametes
Phenotype = 75% wild 6 female: 6 male
25% vestigial 2 female: 2 male
Expected ratio 3:1
Discussion
In the result, I have got 100% of wild (14 male: 14 female) when wild male is crossed with vestigal female in cross 1, 100% of wild (18 male: 18 female). In cross 2 when wild females is crossed with vestigial males and I did self cross with f1 generation from cross1 (wild male with vestigial female) I have got 75 % of wild (9 male: 9females) and 25 % of vestigal (3male:3 female) and self cross with F1 generation from cross 2 (wild male with wild female) I have got 75 % of wild (12 male: 12 female) and 25 % of vestigal (4 male: 4 female). The ratio observed is 3:1 and then when I compared the expected ratio with observed ratio I found out the expected ratio is also 3:1. the wild and vestigal are not sex-linked, because in cross1 I crossed wild males with vestigal females and in cross 2 I crossed wild females with vestigal males and the results I got were 100% of wild in both cross 1 and cross 2 and when I did self cross they both had 3:1 ratio. If they were sex-linked their ratios wouldn’t be 3:1 and they would have different ratios or outcome and from these observations I will say their characteristics are not sec-linked
Sources of error
- There could be less pairing number, because Flies could be killed by overdose of flynap
- Not enough yeast used ( the flies grown eat only yeast given, but there was not enough yeast they may die.
- There could be human error by using the equipments and flies may not be identified properly (males from females)
- May be not all females are virgin and if so it wouldn’t be a pure-breeding