This was group presentation... with lots of good & memorable time....

1. Sex-Linked Inheritance and
Interaction of genes

2. • We were given three culture bottles with Drosophila
melanogaster , one set with red-eye color & two sets
of white -eyed mutants.
• Let one set of white eye mutant be named as “A” and
another set of white eye mutants is named as “B”.
• Before we set up the cross, we cultured the flies, so as
to increase the count of flies.
• The flies were sub-cultured for ten days.
• Approximately we got 150 flies.

3. Culture media
For Drosophila, a satisfactory standard culture medium
must be nutritious, inexpensive, have a high moisture
content and a firm texture, and be resistant to mould and
bacterial contamination. Most standard media contain
sugar source, a grain base, agar, a mould inhibitor and
yeast (Ashburner & Thompson,Jr 1978).

4. Culturing of D.melanogaster
Drosophila was one of the first organisms to be studied
genetically: its small size, short life cycle, high
reproductive rate, and ease of culture. Many different
species, and a large number and wide variety of
naturally-occurring and artificially-induced genetic
variants are available.
Now we should collect virgin females.

6. Importance of Virgin Females
All female flies used in controlled genetic crosses must
be “virgins”. Female flies are capable of mating as early
after emerging from the pupae stage and are
polyandrous, that is, capable of mating with several
males. Once mated, females can retain viable sperm for
several days and this will confuse the results of a
subsequent controlled mating. To prevent this, all adult
flies are removed from the culture bottle prior, so that
all newly hatched flies will remain virgin.

7. Experiment 1

8. After collecting the virgins we have to keep for aging.
Aging is done to know whether the collected virgins are
contaminated or not.
Crosses are set up. In direct cross, 5 virgin red-eyed
female is crossed with 5 white-eyed males(A).
In reciprocal cross, 5 virgin white-eyed females(A) are
crossed with 5 red-eyed males.
We allowed the cross to develop for 8 days.
Then F1 progenies were isolated and phenotypes were
examined.
The observed results are as follows:

9. Direct cross
Reciprocal cross
Reciprocal cross

10. Phenotype Red eye female Red eye male
No. of flies 90 72
F1 Generation
Phenotype Red eye female white eye male
No. of flies 75 63
DIRECT CROSS
RECIPROCAL CROSS

11. By observing F1 progeny of direct and reciprocal cross,
we could analyze that there is no symmetry i.e. they are
asymmetric.
In direct cross all F1 progeny red eyes(100%) is seen
but whereas in reciprocal cross both red and white eyes
are seen(appx. 50:50).
As it shows asymmetry it is not present on autosome,
so it may be present on sex chromosome.
In direct cross, we could only find red eyed F1
progenies. So we suggest that red is the dominant
character.

12. In reciprocal cross only F1 males were white-eyed. This
shows sex bias, hence it is present on sex chromosome.
As only males are affected and females are not affected,
we could predict that the gene is present on X
chromosome
This may be because females consist of two X
chromosome and male only I X chromosome.
May be red-eye is dominant over white-eyed.
By the end of F1 generation, we couldn’t identify the
given flies were either in homozygous or heterozygous
condition.

13. How to identify whether F1 progeny
are in homozygous or heterozygous
condition?

14. To confirm whether the given parental flies are
in homozygous or heterozygous condition we
have to conduct test cross
Test cross was conducted by using virgin F1
female with recessive male parent.

16. DIRECT CROSS RECIPROCAL CROSS
Date RED WHITE RED WHITE
24/10 0 1 3 1 2 3 5 1
25/10 5 7 5 1 4 1 6 4
26/10 6 4 3 5 7 6 2 2
28/10 4 7 6 4 5 7 7 6
29/10 3 2 2 5 7 3 3 4
39 35 45 40
74 85
TEST CROSS

17. By the end of the test cross both direct and reciprocal
cross, we got all possible progenies i.e.,
1. Red-eyed females
2. Red-eyed males
3. White-eyed females and
4. White-eyed males.
Obtained ratio was found
to be 1:1

18. Whether the character
present on one gene or
multiple gene?

19. F1 selfing was carried out so as to confirm how many
genes were controlling the eye trait.
Five F1 females was crossed with five F1 males for
both direct and reciprocal cross.
In direct cross, we got F2 progeny in the ratio of
Red : White
2:1
In reciprocal cross, we got F2 progeny in the ratio of
Red: White
1:1

21. DATE RED EYED FEMALE RED EYED MALE WHITE EYED MALE
24/10/13 34 20 20
25/10/13 40 23 18
26/10/13 35 22 14
28/10/13 39 20 19
29/10/13 35 15 13
183 100 84
DIRECT CROSS F2 PROGENIES

22. DATE RED EYED
FEMALE
RED EYED
MALE
WHITE EYED
FEMALE
WHITE EYED
MALE
24/10/13 35 34 34 37
25/10/13 40 32 30 45
26/10/13 35 39 31 43
28/10/13 42 27 35 35
29/10/13 39 32 25 30
189 164 155 190
RECIPROCAL CROSS F2 PROGENIES

23. CHI SQUARE :DIRECT CROSS
PHENOTYPE OBSERVED
(O)
EXPECTED
(E)
d = O-E d2 d2/E
RED 283 275.25 7.8 60.8 0.221
WHITE 84 91.75 7.5 56.25 0.65
367 0.87
F2

24. CHI SQUARE :RECIPROCAL CROSS
PHENOTYPE OBSERVED
(O)
EXPECTED
(E)
d = O-E d2 d2/E
RED 353 347 4 16 0.04
WHITE 345 349 4 16 0.04
698 0.08
F2

25. CHI SQUARE :TEST CROSS
PHENOTYPE OBSERVED
(O)
EXPECTED
(E)
d = O-E d2 d2/E
RED 39 37 2 4 0.10
WHITE 35 37 2 4 0.10
74 0.2
Direct cross

26. CHI SQUARE :TEST CROSS
PHENOTYPE OBSERVED
(O)
EXPECTED
(E)
d = O-E d2 d2/E
RED 45 42.5 2.5 6.25 0.14
WHITE 40 42.5 2.5 6.25 0.14
85 0.28
Reciprocal

27. Result
Chi square
value (3.84)
Accept or Reject of
data
Direct cross 0.87 accepted
Reciprocal cross 0.08 accepted
Test cross(direct) 0.20 accepted
Test cross (reciprocal) 0.28 accepted
Experimental 1

28. Interpretation
We got 75% of red eyed
F2 progenies which
confirms that red eye is
dominant over white eye.
We got 50:50 F2
progenies both red eye
and white eye.
NORMAL
RECIPROCAL

29. In direct cross, F2 Ratio is appx. 3:1 which is
comparable to Mendel’s monohybrid ratio but in
reciprocal cross, F2 ratio is appx. 1:1 which is
comparable to normal test cross ratio.
Both F1 and F2 progeny did not follow Mendelian ratio,
hence the patter of inheritance is Non-Mendelian.
In reciprocal cross, the white eye character passed from
female to F1 male. Further it was inherited to F2
female.
Here we can see inheritance from grandmother to
granddaughter through son. Therefore criss-cross
pattern of inheritance is seen

31. Criss-cross mode of inheritance is a significant
character of X-linked inheritance.
So, we confirm that the genes controlling the eye colour
present on X chromosome.

32. Experiment 2

33. After collecting the virgins we have to keep for aging.
Aging is done to know whether the collected virgins are
contaminated or not.
Crosses are set up. In direct cross, 5 virgin red-eyed
female is crossed with 5 white-eyed males(B).
In reciprocal cross, 5 virgin white-eyed females(B) are
crossed with 5 red-eyed males.
We allowed the cross to develop for 8 days.
Then F1 progenies were isolated and phenotypes were
examined.
The observed results are as follows:

34. Phenotype Red eye female Red eye male
No. of flies 97 68
F1 Generation
Phenotype Red eye female Red eye male
No. of flies 83 61
DIRECT CROSS
RECIPROCAL CROSS

37. F1 interpretation
Only red eyed females and males as the F1 progenies
there by we could postulate that red eye trait is dominate
over white eyed.
By comparing direct and reciprocal cross we could see a
similarity i.e. symmetry in phenotype of F1 progenies.
Symmetry in F1 progenies, show that the trait
present on autosome.
There is no sex bias seen between the two sexes
as seen in previous experiment.

38. To confirm whether the given parental flies are
in homozygous or heterozygous condition we
have to conduct test cross
Test cross was conducted by using virgin F1
female with recessive male parent.

39. Dates Red Scarlet Brown White
24/10/13 7 4 6 6
25/10/13 6 5 3 3
26/10/13 3 6 5 5
28/10/13 5 2 2 3
29/10/13 2 7 4 4
23 24 20 21
TEST CROSS (direct)
Total Number of Progeny = 86

40. Dates Red Scarlet Brown White
24/10/13 5 4 6 6
25/10/13 6 5 3 3
26/10/13 3 6 5 6
28/10/13 5 2 6 3
29/10/13 2 3 4 4
25 20 24 22
TEST CROSS (reciprocal)
Total Number of Progeny = 91

41. • The test cross ratio of both normal and reciprocal
cross was coinciding with normal mendelian test
cross ratio i.e. 1:1:1:1.
• The test cross progeny of both direct and reciprocal
cross showed 4 types of phenotype i.e. normal red
eyed, brown eyed, scarlet eyed and white eyed.
• We could find two recessive character expressed
independently.
• May F1 was in heterozygous hybrid condition
therefore could produce double recessive progeny,
resulting in scarlet and brown eyed mutant.

42. • To analyze the number of gene controlling the trait F1
selfing was carried out using 5 F1 females and 5 F1
males.
• In the F2 progenies are same for both direct and
reciprocal cross.
• In F2, we obtained 4 types of progenies with different
phenotype like red eyed, brown eyed, scarlet eyed
and white eyed.
• In the F2 progenies, the ratio obtained was appx.
9:3:3:1 which is normal Mendel’s ratio.

44. NORMAL CROSS OK × bw/st
Date Red Brown Scarlet white
24/10 14 15 5 3 7 5 0 0
25/10 15 12 6 7 6 5 2 0
26/10 13 11 5 4 5 6 1 3
28/10 17 13 3 6 6 4 2 2
29/10 21 11 6 4 5 3 1 2
142 49 52 13

45. RECIPROCAL CROSS OK × bw/st
Date Red Brown Scarlet white
24/10 12 12 3 0 0 5 0 0
25/10 17 16 2 5 6 4 2 3
26/10 11 14 6 5 6 5 1 2
28/10 12 14 5 4 4 6 1 4
29/10 15 16 3 3 4 5 2 0
139 50 45 15

46. CHI SQUARE :DIRECT CROSS
PHENOTYPE OBSERVED
(O)
EXPECTED
(E)
d = O-E d2 d2/E
RED 142 255×9 =143.43
16
122-123.75=
1.75
3.062 3.062 =0.024
123.75
SCARLET 49 255x3 =47.81
16
49-47.81=1.19 1.416 1.416 =0.029
47.81
BROWN 52 255×3 =47.81
16
43-41.25 = 1.75 3.062 3.062 =0.074
41.25
WHITE 14 255x1 =15.93
16
13-15.93=-1.93 3.724 3.724 =0.233
15.93
0.36
F2

47. CHI SQUARE : RECIPROCAL CROSS
PHENOTYPE OBSERVED
(O)
EXPECTED
(E)
d = O-E d2 d2/E
RED 139 255×9 =143.437
16
139-143.437=
4.43
19.68 0.13
SCARLET 50 255x3 =47.8125
16
50-47.812=
2.19
4.79 0.10
BROWN 45 255×3 =47.812
16
45-47.812=
2.81
7.89 0.16
WHITE 15 255x1 =15.937
16
15-
15.937=0.937
0.877 0.054
0.44
F2

48. CHI SQUARE :TEST CROSS (DIRECT)
PHENOTYPE OBSERVED
(O)
EXPECTED
(E)
d = O-E d2 d2/E
RED 23 86×1 =21.5
4
1.5 2.25 0.10
SCARLET 24 86x1 =21.5
4
2.5 6.25 0.28
BROWN 20 86×1 =21.5
4
1.5 2.25 0.10
WHITE 21 86x1 =21.5
4
0.5 0.25 0.01
0.49

49. CHI SQUARE :TEST CROSS
(RECIPROCAL)
PHENOTYPE OBSERVED
(O)
EXPECTED
(E)
d = O-E d2 d2/E
RED 24 91×1 =22.75
4
1.25 1.56 0.06
SCARLET 22 91x1 =22.75
4
0.75 0.56 0.024
BROWN 23 91×1 =22.75
4
0.25 0.062 0.10
WHITE 22 91x1 =22.75
4
0.75 0.56 0.024
91 0.15

50. Result
Chi square
value (7.82)
Accept or Reject of
data
Direct cross 0.36 accepted
Reciprocal cross 0.44 accepted
Test cross(direct) 0.49 accepted
Test cross (reciprocal) 0.15 accepted
Experimental 2

51. Reference
• http://www.ou.edu/journals/dis/DIS60/Ramachandr
a%20171.pdf
• www.googleimages.com
• www.wikipedia.com
• www.scienceencyclopedia.com
• http://www.nature.com/scitable/topicpage/thomas-
hunt-morgan-and-sex-linkage-452