Set A showing a collection of human chromosomes with the Y chromosome identified.

To solve this problem, we need to carefully count the number of chromosomes shown in "Set A".

Step 1: Understand what we are counting
The image displays individual chromosomes. In biology diagrams like this, each distinct X-shaped or V-shaped structure represents one chromosome. We need to count every single one of these structures scattered across the white background.

Step 2: Systematic Counting
Let's count them by scanning the image generally from top to bottom, left to right, to ensure we don't miss any or double-count.

* Top Row area:
1. Top-left horizontal pair (looks like two connected, but it's one large metacentric chromosome): 1
2. Below that, small V-shape: 1
3. To the right, large X-shape tilted: 1
4. Next to it, long horizontal striped: 1
5. Above that, small X-shape: 1
6. Far top-right, small V-shape: 1
7. Below that, tiny V-shape: 1
8. Far top-right corner, curved striped: 1
*(Subtotal: 8)*

* Upper-Middle Area:
9. Left side, medium X-shape tilted: 1
10. Center, large long striped X-shape: 1
11. Right of center, large long striped X-shape: 1
12. Far right, vertical striped: 1
13. Below the far right one, small horizontal striped: 1
*(Subtotal: 5, Total so far: 13)*

* Middle Area:
14. Left side, large X-shape tilted left: 1
15. Center-left, very large X-shape tilted right: 1
16. Center, small X-shape: 1
17. Just below that, a tiny Y-shape (or small V): 1
18. Right of center, medium X-shape: 1
19. Far right, small horizontal striped: 1
20. Below that, medium horizontal striped: 1
21. Far right edge, medium X-shape tilted: 1
*(Subtotal: 8, Total so far: 21)*

* Lower-Middle Area:
22. Left edge, curved striped: 1
23. Near left, small horizontal striped: 1
24. Center, medium horizontal striped: 1
25. Right of center, small X-shape: 1
26. Far right, small X-shape: 1
27. Bottom right area, medium X-shape tilted: 1
*(Subtotal: 6, Total so far: 27)*

* Bottom Area:
28. Far left, vertical striped X-shape: 1
29. Left-center, medium X-shape tilted: 1
30. Center, medium horizontal striped: 1
31. Right of center, small X-shape (white/empty looking): 1
32. Far right, small vertical X-shape: 1
33. Bottom left, tiny curved: 1
34. Bottom left corner, vertical striped X-shape: 1
35. Bottom center-left, small X-shape tilted: 1
36. Bottom center, large long striped X-shape: 1
37. Bottom center-right, medium horizontal striped: 1
38. Bottom right, small V-shape: 1
39. Bottom right, medium X-shape tilted: 1
40. Bottom right corner, large horizontal striped: 1
41. Very bottom right edge, vertical striped X-shape: 1

Let me recount more carefully by grouping them visually to be absolutely sure. It is easy to lose track. Let's try counting by columns roughly.

Left Column:
1. Top horizontal large
2. Small V below it
3. Medium X tilted
4. Large X tilted left
5. Curved striped
6. Vertical striped X (middle height)
7. Tiny curved
8. Vertical striped X (bottom)
*(Count: 8)*

Center-Left Column:
9. Large X tilted right (top-ish)
10. Small V (below the first horizontal one) - wait, I counted this in left? No, let's restart with a strict grid method.

Let's divide the image into 4 quadrants.

Top-Left Quadrant:
1. Large horizontal metacentric (top left)
2. Small submetacentric (below #1)
3. Large acrocentric/submetacentric tilted (right of #1)
4. Large metacentric tilted (below #3)
5. Small metacentric (below #4)
6. Large submetacentric tilted left (bottom of quadrant)
7. Small acrocentric (left edge, middle)
*(Total: 7)*

Top-Right Quadrant:
8. Small metacentric (top center)
9. Long submetacentric horizontal (center top)
10. Small submetacentric (right of #8)
11. Tiny submetacentric (far right top)
12. Curved acrocentric (far right corner)
13. Small submetacentric (below #11)
14. Long submetacentric tilted (center right)
15. Vertical acrocentric (far right edge)
16. Small metacentric horizontal (below #15)
17. Small metacentric X (center, below #9) -- wait, this is near the center line.
Let's stick to simple counting again, marking them off mentally.

1. Top-left horizontal
2. Top-left small V
3. Top-mid large tilted X
4. Top-mid long horizontal
5. Top-mid small X
6. Top-right small V
7. Top-right tiny V
8. Top-right curved
9. Mid-left medium tilted X
10. Mid-left large long tilted X
11. Center small X
12. Center tiny Y/V
13. Center-right medium X
14. Center-right long tilted X
15. Far-right vertical
16. Far-right small horizontal
17. Far-right medium horizontal
18. Far-right tilted X
19. Lower-left curved
20. Lower-left small horizontal
21. Lower-mid large tilted X
22. Lower-mid medium horizontal
23. Lower-mid small white X
24. Lower-right small X
25. Lower-right tilted X
26. Bottom-left vertical X
27. Bottom-left tiny curved
28. Bottom-left vertical X (lower)
29. Bottom-mid small tilted X
30. Bottom-mid long horizontal
31. Bottom-mid medium horizontal
32. Bottom-right small V
33. Bottom-right tilted X
34. Bottom-right horizontal
35. Bottom-right vertical X

I seem to be getting around 35-41. Let's do one final, very slow count.

Row 1 (Topmost):
1. Horizontal (Left)
2. Tilted X (Mid-Left)
3. Horizontal (Mid)
4. Small X (Mid-Right)
5. Small V (Right)
6. Curved (Far Right)
*(6)*

Row 2:
7. Small V (Left)
8. Small X (Right, below #4)
9. Tiny V (Far Right, below #6)
*(3)* -> Total 9

Row 3:
10. Tilted X (Left)
11. Long Horizontal (Mid)
12. Long Tilted X (Right)
13. Vertical (Far Right)
*(4)* -> Total 13

Row 4:
14. Large Tilted X (Left)
15. Small X (Center)
16. Tiny Y (Center, below 15)
17. Medium X (Right)
18. Small Horizontal (Far Right)
*(5)* -> Total 18

Row 5:
19. Curved (Left)
20. Small Horizontal (Left-Center)
21. Large Tilted X (Center-Left)
22. Medium Horizontal (Center)
23. Small White X (Right)
24. Small X (Far Right)
25. Tilted X (Far Right, lower)
*(7)* -> Total 25

Row 6:
26. Vertical X (Far Left)
27. Tilted X (Left)
28. Medium Horizontal (Center)
29. Small Horizontal (Right)
30. Small Vertical X (Far Right)
*(5)* -> Total 30

Row 7 (Bottom):
31. Tiny Curved (Left)
32. Vertical X (Far Left)
33. Small Tilted X (Left-Center)
34. Long Horizontal (Center)
35. Medium Horizontal (Right-Center)
36. Small V (Right)
37. Tilted X (Right)
38. Horizontal (Far Right)
39. Vertical X (Far Right Corner)
*(9)* -> Total 39

Let me re-verify the bottom right area.
Below #29 (Small Horizontal), there is #36 (Small V), #37 (Tilted X), #38 (Horizontal), #39 (Vertical).
Wait, look at the cluster in the bottom right.
There is a small V (#36).
To its right is a tilted X (#37).
Below that is a horizontal one (#38).
And on the very edge is a vertical one (#39).
That looks correct.

Let's re-verify the center-bottom.
#34 is the long horizontal one.
#35 is the medium horizontal one to its right.
#33 is the small tilted one to its left.
#32 is the vertical one on the far left.
#31 is the tiny curved one above #32.

Let's re-verify the left side.
#26 Vertical X (middle height).
#27 Tilted X (below #26).
#19 Curved (above #26).
#14 Large Tilted X (above #19).
#10 Tilted X (above #14).
#7 Small V (above #10).
#1 Horizontal (top).
This column seems consistent.

Let's re-verify the center stack.
Top: #3 Horizontal, #4 Small X.
Mid: #11 Long Horizontal, #15 Small X, #16 Tiny Y.
Lower Mid: #21 Large Tilted, #22 Medium Horizontal, #23 Small White X.
Bottom: #28 Medium Horizontal, #34 Long Horizontal.
This seems consistent.

Let's re-verify the right side stack.
Top: #5 Small V, #6 Curved, #9 Tiny V.
Mid: #12 Long Tilted, #13 Vertical, #18 Small Horizontal, #24 Small X, #25 Tilted X.
Lower: #17 Medium X (wait, #17 was "Medium X (Right)" in Row 4. Let's trace it. Yes, between #16 and #18).
Bottom: #29 Small Horizontal, #30 Small Vertical X, #36 Small V, #37 Tilted X, #38 Horizontal, #39 Vertical X.

Let's list them all again to be precise.
1. Top Left Horizontal
2. Top Left Small V
3. Top Mid Tilted X
4. Top Mid Horizontal Long
5. Top Mid Small X
6. Top Right Small V
7. Top Right Tiny V
8. Top Right Curved
9. Mid Left Tilted X
10. Mid Left Long Tilted X
11. Center Small X
12. Center Tiny Y
13. Center Right Medium X
14. Center Right Long Tilted X
15. Far Right Vertical
16. Far Right Small Horizontal
17. Far Right Medium Horizontal (Wait, looking at the image, below #15 Vertical is #16 Small Horizontal. Below that is #24 Small X? No. Let's look at the group on the right edge.)

Right Edge Group:
- Top: Curved (#8)
- Below that: Tiny V (#7) -- actually #7 is to the left of #8.
- Below that: Vertical (#15)
- Below that: Small Horizontal (#16)
- Below that: Small X (#24) -- This is the one labeled #24 in my previous count.
- Below that: Tilted X (#25)
- Below that: Small Vertical X (#30)
- Below that: Small V (#36) -- Wait, #36 is further left.
- Below that: Tilted X (#37)
- Below that: Horizontal (#38)
- Below that: Vertical X (#39)

Let's check the items between the Center and Right Edge.
- Top: Small X (#5)
- Below that: Long Tilted X (#14)
- Below that: Medium X (#13) -- Wait, #13 is "Center Right Medium X".
- Below that: Small Horizontal (#18) -- Wait, #18 was "Small Horizontal (Far Right)" in Row 4. Let's look at the image. There is a small horizontal chromosome below the long tilted one (#14). Let's call this #A.
- Below that: Small White X (#23)
- Below that: Small Horizontal (#29) -- Wait, #29 was "Small Horizontal (Right)" in Row 6.
- Below that: Small V (#36) is to the left of the bottom-right cluster.

Okay, let's just count every single item one last time, crossing them off.

1. Top-left horizontal
2. Below it, small V
3. Right of 1, large tilted X
4. Right of 3, long horizontal
5. Above 4, small X
6. Right of 5, small V
7. Right of 6, tiny V
8. Right of 7, curved
9. Below 2, medium tilted X
10. Right of 9, large long tilted X
11. Right of 10, small X
12. Below 11, tiny Y
13. Right of 11, medium X
14. Right of 13, long tilted X
15. Right of 14, vertical
16. Below 15, small horizontal
17. Below 9, large tilted X (left side)
18. Left of 17, curved
19. Below 18, small horizontal
20. Right of 17, large tilted X (center)
21. Right of 20, medium horizontal
22. Right of 21, small white X
23. Right of 22, small X (edge)
24. Below 23, tilted X (edge)
25. Below 13, small horizontal (this is #18 in previous count)
26. Below 25, small X (this is #29 in previous count? No, let's look at the gap between #22 and #24).
Actually, looking at the right side again:
- Vertical (#15)
- Small Horizontal (#16)
- Then there is a gap.
- Then Small X (#23)
- Then Tilted X (#24)
- Then Small Vertical X (#30)
- Then Small V (#36) is to the left.
- Then Tilted X (#37)
- Then Horizontal (#38)
- Then Vertical X (#39)

Where did #25, #29 go?
Let's look at the cluster below #22 (Small White X).
Below #22 is #29 (Small Horizontal).
To the right of #29 is #30 (Small Vertical X).

Let's look at the cluster below #13 (Medium X).
Below #13 is #25 (Small Horizontal).

So:
25. Small Horizontal (below #13)
26. Small Horizontal (below #22, which is #29 previously) -> Let's call this #26.

Now Bottom Row:
27. Far Left Vertical X
28. Above 27, Tiny Curved
29. Left of 27, nothing.
30. Right of 27, Small Tilted X
31. Right of 30, Long Horizontal
32. Right of 31, Medium Horizontal
33. Right of 32, Small V
34. Right of 33, Tilted X
35. Right of 34, Horizontal
36. Right of 35, Vertical X

Wait, I missed some in the middle-left bottom.
Below #17 (Large Tilted Left) is #27 (Far Left Vertical)? No.
Let's trace the left column down.
1. Top Horizontal
2. Small V
9. Medium Tilted X
17. Large Tilted X
18. Curved
19. Small Horizontal
27. Vertical X (This is the one at the very bottom left corner? No, there are two vertical ones on the left).

Let's look at the bottom left corner specifically.
There is a Vertical X at the very bottom (#32 in new count).
Above it is a Tiny Curved (#31 in new count? No, #28).
Above that is... nothing immediately.
To the right of the bottom Vertical X is a Small Tilted X (#33).

Let's look at the one above the Tiny Curved.
That is #19 (Small Horizontal).
Above that is #18 (Curved).
Above that is #17 (Large Tilted).

So the left-most column has:
1. Top Horizontal
2. Small V
9. Medium Tilted
17. Large Tilted
18. Curved
19. Small Horizontal
28. Tiny Curved
32. Vertical X

That's 8 items on the far left strip.

Now the next strip inward (Center-Left):
3. Top Tilted X
10. Top Long Tilted X
20. Mid Large Tilted X
33. Bottom Small Tilted X

That's 4 items.

Center Strip:
4. Top Long Horizontal
5. Top Small X
11. Mid Small X
12. Mid Tiny Y
21. Mid Medium Horizontal
34. Bottom Long Horizontal

That's 6 items.

Center-Right Strip:
13. Mid Medium X
25. Low Small Horizontal (below #13)
22. Low Small White X (below #21? No, #22 is right of #21).
26. Low Small Horizontal (below #22)
35. Bottom Medium Horizontal

That's 5 items.

Right Strip:
6. Top Small V
7. Top Tiny V
8. Top Curved
14. Mid Long Tilted
15. Mid Vertical
16. Mid Small Horizontal
23. Low Small X
24. Low Tilted X
30. Low Small Vertical X (Wait, #30 was "Small Vertical X" in previous count. It is below #24).
36. Bottom Small V
37. Bottom Tilted X
38. Bottom Horizontal
39. Bottom Vertical X

That's 13 items.

Total = 8 (Left) + 4 (C-Left) + 6 (Center) + 5 (C-Right) + 13 (Right) = 36.

Let me double check the "Right Strip" count.
6, 7, 8, 14, 15, 16, 23, 24, 30, 36, 37, 38, 39.
Are 36, 37, 38, 39 all in the right strip?
36 (Small V) is near the bottom right.
37 (Tilted X) is next to it.
38 (Horizontal) is below 37.
39 (Vertical X) is on the edge.
Yes.

Are 23, 24, 30 in the right strip?
23 (Small X) is on the edge, below #16.
24 (Tilted X) is below #23.
30 (Small Vertical X) is below #24.
Yes.

Are 6, 7, 8, 14, 15, 16 in the right strip?
6 (Small V) top right.
7 (Tiny V) top right.
8 (Curved) top right corner.
14 (Long Tilted) mid right.
15 (Vertical) mid right edge.
16 (Small Horizontal) below #15.
Yes.

So Right Strip is 13.

Let me double check "Center-Right Strip".
13 (Medium X) - yes.
25 (Small Horizontal) - below #13. Yes.
22 (Small White X) - This is to the right of #21 (Medium Horizontal). Is it in C-Right or Right? It's fairly central. Let's keep it in C-Right.
26 (Small Horizontal) - Below #22. Yes.
35 (Medium Horizontal) - Bottom row, right of center. Yes.

So C-Right is 5.

Let me double check "Center Strip".
4 (Long Horizontal) - Top. Yes.
5 (Small X) - Top. Yes.
11 (Small X) - Mid. Yes.
12 (Tiny Y) - Mid. Yes.
21 (Medium Horizontal) - Low Mid. Yes.
34 (Long Horizontal) - Bottom. Yes.

So Center is 6.

Let me double check "Center-Left Strip".
3 (Top Tilted X) - Yes.
10 (Top Long Tilted X) - Yes.
20 (Mid Large Tilted X) - Yes.
33 (Bottom Small Tilted X) - Yes.

So C-Left is 4.

Let me double check "Left Strip".
1 (Top Horizontal) - Yes.
2 (Small V) - Yes.
9 (Medium Tilted X) - Yes.
17 (Large Tilted X) - Yes.
18 (Curved) - Yes.
19 (Small Horizontal) - Yes.
28 (Tiny Curved) - Yes.
32 (Vertical X) - Yes.

So Left is 8.

Total: 8 + 4 + 6 + 5 + 13 = 36.

Let me do a quick sanity check by counting groups of 5.
Top row: 1,2,3,4,5 (5)
Next down: 6,7,8,9,10 (5) -> 10
Next down: 11,12,13,14,15 (5) -> 15
Next down: 16,17,18,19,20 (5) -> 20
Next down: 21,22,23,24,25 (5) -> 25
Next down: 26,27(missing? no 27 is not in my list, ah, I skipped a number in the sequential assignment but not the count), 28,29(missing?), 30.

Let's map my sequential IDs to the visual flow again to ensure no skips.
My strips method yielded 36.

Let's try one more count, just clicking them off.
1, 2, 3, 4, 5, 6, 7, 8 (Top area)
9, 10, 11, 12, 13, 14, 15, 16 (Upper Mid area)
17, 18, 19, 20, 21, 22, 23, 24, 25 (Lower Mid area)
26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36 (Bottom area)

Let's verify the bottom area count (11 items?).
Items in bottom third:
- Left: Tiny Curved, Vertical X, Small Tilted X. (3)
- Center: Long Horizontal, Medium Horizontal. (2)
- Right: Small Horizontal (from C-Right strip #26), Small Vertical X (#30), Small V (#36), Tilted X (#37), Horizontal (#38), Vertical X (#39).
Wait, #26 is "Low Small Horizontal" in C-Right. It is in the bottom third.
So Right side bottom third has: #26, #30, #36, #37, #38, #39. (6 items).
Total bottom third = 3 (Left) + 2 (Center) + 6 (Right) = 11 items.

Items in Middle Third:
- Left: Curved (#18), Small Horizontal (#19). (2)
- C-Left: Large Tilted X (#20). (1)
- Center: Medium Horizontal (#21), Small White X (#22). (2)
- C-Right: Small Horizontal (#25), Small X (#23). (2) -- Wait, #23 is Right Strip.
- Right: Small Horizontal (#16), Long Tilted (#14), Vertical (#15), Small X (#23), Tilted X (#24). (5)
- Also #13 (Medium X) is in Upper Mid/Lower Mid boundary. Let's put it in Middle.
- Also #11, #12 are Center.

This is getting confusing. The strip method was cleaner.

Strip Method Result: 36.

Let's check if I missed any "hidden" ones.
Sometimes small ones are hard to see.
- Between #11 and #13? No.
- Between #21 and #22? No.
- Between #34 and #35? No.

Let's assume the count is 36.

Final Answer: 36