DNA sequencing

• US 5,360,523 A
• Filed: 02/17/1993
• Issued: 11/01/1994
• Est. Priority Date: 03/29/1984
• Status: Expired due to Fees

• Current Assignee: Li & S Company Limited (Yesco Holdings Co., Ltd.)
• Original Assignee: Li & S Company Limited (Yesco Holdings Co., Ltd.)
• Inventors: Eckles, Robert D., Middendorf, Lyle R., Bruce, Robert C.
• Primary Examiner(s): Niebling, John
• Assistant Examiner(s): STARSIAK, JOHN S
• Application Number:
  US08/018,806
• Time in Patent Office: 622 Days
• Field of Search: 204/299 R, 204/182.8, 356/344
• US Class Current: 204/457
• CPC Class Codes: C07D 209/60 Naphtho [b] pyrroles; Hydrogenated naphtho [b] pyrroles
• CPC Class Codes: C09B 23/0066 the polymethine chain being part of a carbocyclic ring,(e.g. benzene, naphtalene, cyclohexene, cyclobutenene-quadratic acid)
• CPC Class Codes: C12Q 1/6869 Methods for sequencing
• CPC Class Codes: C12Q 2563/107 fluorescence
• CPC Class Codes: C12Q 2565/125 Electrophoretic separation
• CPC Class Codes: G01N 2021/6417 Spectrofluorimetric devices
• CPC Class Codes: G01N 21/6428 Measuring fluorescence of fluorescent products of reactions or of fluorochrome labelled reactive substances, e.g. measuring quenching effects, using measuring "optrodes" in vivo A61B5/00; immunoassay G01N33/53
• CPC Class Codes: G01N 27/447 using electrophoresis
• CPC Class Codes: G01N 27/44721 by optical means
• CPC Class Codes: G01N 27/44726 using specific dyes, markers or binding molecules

Abstract

To sequence DNA, DNA samples marked with fluorescent infrared dye are applied at a plurality of locations for electrophoresing in a plurality of channels through a gel electrophoresis slab. The channels are scanned with a laser and a sensor, that include a microscope focused on the gel slab. The focal point and slab are adjusted with respect to each other so that the focal point of the microscope remains on the gel slab during a scan. The data from the scan is directly used to amplitude modulate density readings on a display, and the scan is displayed in a horizontal sweep of a cathode ray tube, whereby said cathode ray tube provides intensity displays of bands representing DNA. Different sizes of glass gel sandwiches may be mounted to the same console for different sequencing tasks.

Claims

1. A method for sequencing DNA comprising:

applying fluorescently marked DNA samples at a plurality of locations for electrophoresing in a plurality of channels through a gel electrophoresis slab;

establishing electrical potential across said gel electrophoresis slab wherein DNA samples are resolved in accordance with the size of DNA fragments in said gel electrophoresis slab into fluorescently marked DNA bands;

moving a scanning means with a carriage assembly a direction substantially perpendicular to a direction of the plurality of channels; and

scanning the separated samples photoelectrically with a laser and a sensor mounted to the carriage assembly, wherein the laser scans with scanning light at

a scanning light frequency within an absorbent spectrum of said fluorescently marked DNA samples and sensing light at an emission frequency of the marked DNA;

said step of scanning including the substeps of focusing a microscope on a gel portion of an electrophoresis slab at least at two different locations along a path of a single scan.

2. A method for sequencing DNA comprising:

applying fluorescently marked DNA samples at a plurality of locations for electrophoresing in a plurality of channels through a gel electrophoresis slab;

establishing electrical potential across said gel electrophoresis slab wherein DNA samples are resolved in accordance with the size of DNA fragments in said gel electrophoresis slab into fluorescently marked DNA bands; and

scanning the separated samples photoelectrically with a laser and a sensor, wherein the laser scans with scanning light at a scanning light frequency within an absorbent spectrum of said fluorescently marked DNA samples and sensing light at an emission frequency of the marked DNA;

said step of scanning including the substeps of focusing a microscope on a gel portion of an electrophoresis slab at least at two different locations along a path of a single scan;

said step of focusing at one location including the step of adjusting the focal point of a lens of the microscope and the step of focusing at the other point including the step of adjusting the distance between the gel and the microscope.

3. A method in accordance with claim 2 in which said microscope is focused before taking data on a complete scan and the distance between the microscope and said electrophoresis slab adjusted, after which a complete scan is made and data taken.

4. A method for sequencing DNA comprising:

applying fluorescently marked DNA samples at a plurality of locations for electrophoresing in a plurality of channels through a gel electrophoresis slab;

establishing electrical potential across said gel electrophoresis slab wherein DNA samples are resolved in accordance with the size of DNA fragments in said gel electrophoresis slab into fluorescently marked DNA bands; and

scanning the separated samples photoelectrically with a laser and a sensor, wherein the laser scans with scanning light at a scanning light frequency within an absorbent spectrum of said fluorescently marked DNA samples and sensing light at an emission frequency of the marked DNA;

said step of scanning including the substeps of focusing a microscope on a gel portion of an electrophoresis slab at least at two different locations along a path of a single scan;

the step of focusing in said one location including the step of adjusting the focal point of a lens and the step of focusing at said at least one other location including the step of refocusing the lens at a distance no more than ten inches from said first location, said steps of focusing including at least two other further steps of focusing by adjusting the lens of the microscope.

5. A method for sequencing DNA comprising:

applying fluorescently marked DNA samples at a plurality of locations for electrophoresing in a plurality of channels through a gel electrophoresis slab;

establishing electrical potential across said gel electrophoresis slab wherein DNA samples are resolved in accordance with the size of DNA fragments in said gel electrophoresis slab into fluorescently marked DNA bands; and

scanning the separated samples photoelectrically with a laser and a sensor, wherein the laser scans with scanning light at a scanning light frequency within an absorbent spectrum of said fluorescently marked DNA samples and sensing light at an emission frequency of the marked DNA;

said step of scanning including the substeps of focusing a microscope on a gel portion of an electrophoresis slab at least at two different locations along a path of a single scan;

the step of focusing including the step of locating a first and second glass plate by the amount of fluorescence emitted by the glass plates and focusing on the gel between the plates by detecting a different amount of fluorescence in the gel.

6. A method in accordance with claim 5 in which the microscope is refocused a plurality of times in each scan.

7. A method for sequencing DNA comprising:

applying fluorescently marked DNA samples at a plurality of locations for electrophoresing in a plurality of channels through a gel electrophoresis slab;

establishing electrical potential across said gel electrophoresis slab wherein DNA samples are resolved in accordance with the size of DNA fragments in said gel electrophoresis slab into fluorescently marked DNA bands; and

scanning the separated samples photoelectrically with a laser and a sensor, wherein the laser scans with scanning light at a scanning light frequency within an absorbent spectrum of said fluorescently marked DNA samples and sensing light at an emission frequency of the marked DNA;

said step of scanning including the substeps of focusing a microscope on a gel portion of an electrophoresis slab at least at two different locations along a path of a single scan to scan same, wherein a plurality of readings of data are taken at a plurality of different points in a scan and those readings averaged.

8. A method for sequencing DNA comprising:

applying fluorescently marked DNA samples at a plurality of locations for electrophoresing in a plurality of channels through a gel electrophoresis slab;

establishing electrical potential across said gel electrophoresis slab wherein DNA samples are resolved in accordance with the size of DNA fragments in said gel electrophoresis slab into fluorescently marked DNA bands; and

scanning the separated samples photoelectrically with a laser and a sensor, wherein the laser scans with scanning light at a scanning light frequency within an absorbent spectrum of said fluorescently marked DNA samples and sensing light at an emission frequency of the marked DNA;

said step of scanning including the substeps of focusing a microscope on a gel portion of an electrophoresis slab at least at two different locations along a path of a single scan to scan same, wherein data from said scan is directly used to amplitude modulate density readings on a display;

said scan is displayed in a vertical sweep of a cathode ray tube, whereby said cathode ray tube provides intensity displays of bands representing DNA.

9. A method for sequencing DNA comprising:

applying fluorescently marked DNA samples at a plurality of locations for electrophoresing in a plurality of channels through a gel electrophoresis slab;

establishing electrical potential across said gel electrophoresis slab wherein DNA samples are resolved in accordance with the size of DNA fragments in said gel electrophoresis slab into fluorescently marked DNA bands; and

scanning the separated samples photoelectrically with a laser and a sensor, wherein the laser scans with scanning light at a scanning light frequency within an absorbent spectrum of said fluorescently marked DNA samples and sensing light at an emission frequency of the marked DNA;

said step of scanning including the substeps of focusing a microscope on a gel portion of an electrophoresis slab at least at two different locations along a path of a single scan, wherein said scanning means is aligned with said gel and the bands are scanned while still in the gel but after being resolved.

10. A method for sequencing DNA comprising:

applying fluorescently marked DNA samples at a plurality of locations for electrophoresing in a plurality of channels through a gel electrophoresis slab;

establishing electrical potential across said gel electrophoresis slab wherein DNA samples are resolved in accordance with the size of DNA fragments in said gel electrophoresis slab into fluorescently marked DNA bands;

scanning the separated samples photoelectrically with a laser and a sensor, wherein the laser scans with scanning light at a scanning light frequency within an absorbent spectrum of said fluorescently marked DNA samples and sensing light at an emission frequency of the marked DNA;

said step of scanning including the substeps of focusing a microscope on a gel portion of an electrophoresis slab at least at two different locations along a path of a single scan, wherein said scanning means is aligned with said gel and the bands are scanned while still in the gel but after being resolved; and

resolving the bands within at least one channel so that the bands of the more mobile strands in the channel are fully resolved while some of the less mobile strands to be later formed into bands are unresolved in a continuous process such that at least ten percent of the bands are fully resolved while the less mobile strands are yet unresolved into bands in the channel.

11. A method of DNA sequencing comprising the steps of:

applying opposite polarity electrical potentials to a first and at least a second buffer;

applying fluorescently marked DNA strands to a plurality of channels of gel, whereby said fluorescently marked DNA strands are electrophoresed along said gel so that the bands of more mobile strands in at least one channel are fully resolved while some of the less mobile strands to be later formed into bands are unresolved in a continuous process;

focusing a microscope wherein the focus point of the microscope is within the gel during a scan;

moving the microscope and laser across said channels, wherein light emitted from the laser and said microscope scans across said channels; and

detecting fluorescent light emitted by said fluorescently marked DNA strands, whereby the time sequence of separated bands may be obtained.

12. A method of DNA sequencing comprising the steps of:

applying opposite polarity electrical potentials to a first and at least a second buffer;

applying fluorescently marked DNA strands to a plurality of channels of gel, whereby said fluorescently marked DNA strands are electrophoresed along said gel so that the bands of more mobile strands in at least one channel are fully resolved while some of the less mobile strands to be later formed into bands are unresolved in a continuous process;

focusing a microscope wherein the focus point of the microscope is within the gel during a scan; and

scanning across said channels with light emitted from a laser and with said microscope;

detecting fluorescent light emitted by said fluorescently marked DNA strands, whereby the time sequence of separated bands may be obtained, wherein light from said laser is in the band incorporating at least the near infrared and infrared regions and said detector responds to light in a band including at least said near infrared and infrared regions.

13. A method of DNA sequencing comprising the steps of:

applying opposite polarity electrical potentials to a first and at least a second buffer;

applying fluorescently marked DNA strands to a plurality of channels of gel, whereby said fluorescently marked DNA strands are electrophoresed along said gel so that the bands of more mobile strands in at least one channel are fully resolved while some of the less mobile strands to be later formed into bands are unresolved in a continuous process;

focusing a microscope wherein the focus point of the microscope is within the gel during a scan;

scanning across said channels with light emitted from a laser and with said microscope; and

detecting fluorescent light emitted by said fluorescently marked DNA strands, whereby the time sequence of separated bands may be obtained;

the step of focusing said microscope including the step of adjusting the distance between said microscope and said gel wherein the distance does not vary more than five percent during a scan.

14. A method of DNA sequencing comprising the steps of:

applying opposite polarity electrical potentials to a first and at least a second buffer;

applying fluorescently marked DNA strands to a plurality of channels of gel, whereby said fluorescently marked DNA strands are electrophoresed along said gel so that the bands of more mobile strands in at least one channel are fully resolved while some of the less mobile strands to be later formed into bands are unresolved in a continuous process;

focusing a microscope wherein the focus point of the microscope is within the gel during a scan; and

scanning across said channels with light emitted from a laser and with said microscope;

detecting fluorescent light emitted by said fluorescently marked DNA strands, whereby the time sequence of separated bands may be obtained;

the step of focusing including the step of dynamically refocusing at a plurality of locations to maintain the focal point within an area of low radiation between two layers of higher radiation whereby said focal point is in the gel between two glass plates on either side of the gel.

15. A method of DNA sequencing comprising the steps of:

applying opposite polarity electrical potentials to a first and at least a second buffer;

applying fluorescently marked DNA strands to a plurality of channels of gel whereby said fluorescently marked DNA strands are electrophoresed along said gel so that the bands of more mobile strands in at least one channel are fully resolved while some of the less mobile strands to be later formed into bands are unresolved in a continuous process;

focusing a microscope wherein the focus point of the microscope is within the gel during a scan;

scanning across said channels with light emitted from a laser and with said microscope; and

detecting fluorescent light emitted by said fluorescently marked DNA strands, whereby the time sequence of separated bands may be obtained, wherein the step of focusing includes the step of focusing at one location;

moving the microscope along a scan to another location; and

adjusting the distance between the microscope and the gel until the microscope can remain focused during at least a portion of the scan.

16. A method of DNA sequencing comprising the steps of:

applying opposite polarity electrical potentials to a first and at least a second buffer;

applying fluorescently marked DNA strands to a plurality of channels of gel, whereby said fluorescently marked DNA strands are electrophoresed along said gel so that the bands of more mobile strands in at least one channel are fully resolved while some of the less mobile strands to be later formed into bands are unresolved in a continuous process;

focusing a microscope wherein the focus point of the microscope is within the gel during a scan;

scanning across said channels with light emitted from a laser and with said microscope;

detecting fluorescent light emitted by said fluorescently marked DNA strands, whereby the time sequence of separated bands may be obtained;

transmitting intensity data to a cathode ray tube so that the intensity data extends substantially across a horizontal sweep of the cathode ray tube;

modulating an electron gun of the cathode ray tube with said intensity data during horizontal sweeps; and

spacing said horizontal sweeps vertically to present a plurality of bands.

17. Apparatus for sequencing DNA comprising:

means for applying fluorescently marked DNA samples at a plurality of locations for electrophoresing in a plurality of channels through a gel electrophoresis slab;

means for establishing electrical potential across said gel electrophoresis slab wherein DNA samples are resolved in accordance with the size of DNA fragments in said gel electrophoresis slab into fluorescently marked DNA bands; and

means for scanning the separated samples photoelectrically with a laser and a sensor, wherein the laser scans with scanning light at a scanning light frequency within an absorbent spectrum of said fluorescently marked DNA samples as the sensor and scanner move in a direction transverse to the channels;

said sensor including means for sensing light at an emission frequency of the marked DNA; and

said means for scanning including means for focusing a microscope on the gel portion of the electrophoresis slab at least at two different locations along the path of a single scan.

18. Apparatus for sequencing DNA comprising:

means for applying fluorescently marked DNA samples at a plurality of locations for electrophoresing in a plurality of channels through a gel electrophoresis slab;

means for establishing electrical potential across said gel electrophoresis slab wherein DNA samples are resolved in accordance with the size of DNA fragments in said gel electrophoresis slab into fluorescently marked DNA bands; and

means for scanning the separated samples photoelectrically with a laser and a sensor, wherein the laser scans with scanning light at a scanning light frequency within an absorbent spectrum of said fluorescently marked DNA samples and sensing light at an emission frequency of the marked DNA;

said means for scanning including means for focusing a microscope on the gel portion of the electrophoresis slab at least at two different locations along the path of a single scan;

said means for focusing at one location including means for adjusting the focal point of the lens of a microscope and means for adjusting the distance between the gel and the microscope.

19. Apparatus in accordance with claim 18 in which the means for focusing in said one location includes means for adjusting the focal point of the lens and the means for focusing at said at least one other location includes means for refocusing the lens at a distance no more than ten inches from said first location, wherein the lens of the microscope may be adjusted at least two further times to focus the microscope during a scan.

20. Apparatus in accordance with claim 18 wherein said means for focusing includes means for focusing before taking data on a complete scan and the distance between the microscope and a plate adjusted, after which a complete scan is made and data taken.

21. Apparatus for sequencing DNA comprising:

means for applying fluorescently marked DNA samples at a plurality of locations for electrophoresing in a plurality of channels through a gel electrophoresis slab;

means for establishing electrical potential across said gel electrophoresis slab wherein DNA samples are resolved in accordance with the size of DNA fragments in said gel electrophoresis slab into fluorescently marked DNA bands; and

means for scanning the separated samples photoelectrically with a laser and a sensor wherein the laser scans with scanning light at a scanning light frequency within an absorbent spectrum of said fluorescently marked DNA samples and sensing light at an emission frequency of the marked DNA;

said means for scanning including means for focusing a microscope on the gel portion of the electrophoresis slab at least at two different locations along the path of a single scan;

the means for focusing including means for locating a first and second glass plate by the amount of fluorescence emitted by the glass plates and focusing on the gel between the plates by detecting a different amount of fluorescence in the gel.

22. Apparatus in accordance with claim 21 in which the microscope is refocused a plurality of times in each scan.

23. Apparatus for sequencing DNA comprising:

means for applying fluorescently marked DNA samples at a plurality of locations for electrophoresing in a plurality of channels through a gel electrophoresis slab;

means for establishing electrical potential across said gel electrophoresis slab wherein DNA samples are resolved in accordance with the size of DNA fragments in said gel electrophoresis slab into fluorescently marked DNA bands;

means for scanning the separated samples photoelectrically with a laser and a sensor, wherein the laser scans with scanning light at a scanning light frequency within an absorbent spectrum of said fluorescently marked DNA samples and sensing light at an emission frequency of the marked DNA;

said means for scanning including means for focusing a microscope on the gel portion of the electrophoresis slab at least at two different locations along the path of a single scan; and

means for obtaining a plurality of readings of data that are taken at a plurality of different points in a scan and those readings averaged.

24. Apparatus for sequencing DNA comprising:

means for applyinq fluorescently marked DNA samples at a plurality of locations for electrophoresing in a plurality of channels through a gel electrophoresis slab;

means for establishing electrical potential across said gel electrophoresis slab wherein DNA samples are resolved in accordance with the size of DNA fragments in said gel electrophoresis slab into fluorescently marked DNA bands;

means for scanning the separated samples photoelectrically with a laser and a sensor, wherein the laser scans with scanning light at a scanning light frequency within an absorbent spectrum of said fluorescently marked DNA samples and sensing light at an emission frequency of the marked DNA;

said means for scanning including means for focusing a microscope on the gel portion of the electrophoresis slab at least at two different locations along the path of a single scan; and

means for directly using the data from said scan to amplitude modulate density readings on a display, wherein said scan is displayed in a vertical sweep of a cathode ray tube, whereby said cathode ray tube provides intensity displays of bands representing DNA.

25. Apparatus for sequencing DNA comprising:

means for applying fluorescently marked DNA samples at a plurality of locations for electrophoresing in a plurality of channels through a gel electrophoresis slab;

means for establishing electrical potential across said gel electrophoresis slab wherein DNA samples are resolved in accordance with the size of DNA fragments in said gel electrophoresis slab into fluorescently marked DNA bands; and

means for scanning the separated samples photoelectrically with a laser and a sensor, wherein the laser scans with scanning light at a scanning light frequency within an absorbent spectrum of said fluorescently marked DNA samples and sensing light at an emission frequency of the marked DNA;

said means for scanning including means for focusing a microscope on the gel portion of the electrophoresis slab at least at two different locations along the path of a single scan, wherein said scanning means is aligned with said gel and the bands are scanned while still in the gel but after being resolved.

26. Apparatus in accordance with claim 25 further including means for resolving the bands within at least one channel so that the bands of more mobile strands in the channel are fully resolved while some of the less mobile strands to be later formed into bands are unresolved in a continuous process such that at least ten percent of the bands are fully resolved while the less mobile strands are yet unresolved into bands in the channel.

27. Apparatus of DNA sequencing comprising:

means for applying opposite polarity electrical potentials to a first and at least a second buffer;

means for applying fluorescently marked DNA strands to a plurality of channels of gel, whereby said fluorescently marked DNA strands are electrophoresed along said gel so that the bands of more mobile strands in at least one channel are fully resolved while some of the less mobile strands to be later formed into bands are unresolved in a continuous process;

means for focusing a microscope wherein the focus point of the microscope is within the gel during a scan;

means for scanning across said channels with light emitted from a laser and with said microscope; and

means for detecting fluorescent light emitted by said fluorescently marked strands, whereby the time sequence of separated bands may be obtained.

28. Apparatus for DNA sequencing comprising:

means for applying opposite polarity electrical potentials to a first and at least a second buffer;

means for applying fluorescently marked DNA strands to a plurality of channels of gel, whereby said fluorescently marked DNA strands are electrophoresed along said gel so that the bands of are mobile strands in at least one channel are fully resolved while some of the less mobile strands to be later formed into bands are unresolved in a continuous process;

means for focusing a microscope wherein the focus point of the microscope is within the gel during a scan;

means for scanning across said channels with light emitted from a laser and with said microscope; and

means for detecting fluorescent light emitted by said fluorescently marked strands, whereby the time sequence of separated bands may be obtained, wherein light from said laser is in the band incorporating at least the near infrared and infrared regions and said detector responds to light in a band including at least said near infrared and infrared regions.

29. Apparatus for DNA sequencing comprising:

means for applying opposite polarity electrical potentials to a first and at least a second buffer;

means for applying fluorescently marked DNA strands to a plurality of channels of gel, whereby said fluorescently marked DNA strands are electrophoresed along said gel so that the bands of more mobile strands in at least one channel are fully resolved while some of the less mobile strands to be later formed into bands are unresolved in a continuous process;

means for focusing a microscope wherein the focus point of the microscope is within the gel during a scan;

means for scanning across said channels with light emitted from a laser and with said microscope; and

means for detecting fluorescent light emitted by said fluorescently marked strands, whereby the time sequence of separated bands may be obtained;

the means for focusing said microscope including means for adjusting the distance between said microscope and said gel wherein the distance does not vary more than five percent during a scan.

30. Apparatus for DNA sequencing comprising:

means for applying opposite polarity electrical potentials to a first and at least a second buffer;

means for applying fluorescently marked DNA strands to a plurality of channels of gel, whereby said fluorescently marked DNA strands are electrophoresed along said gel so that the bands of more mobile strands in at least one channel are fully resolved while some of the less mobile strands to be later formed into bands are unresolved in a continuous process;

means for focusing a microscope wherein the focus point of the microscope is within the gel during a scan;

means for scanning across said channels with light emitted from a laser and with said microscope; and

means for detecting fluorescent light emitted by said fluorescently marked strands, whereby the time sequence of separated bands may be obtained the means for focusing including means for dynamically refocusing at a plurality of locations to maintain the focal point within an area of low radiation between two layers of higher radiation whereby said focal point is in the gel between two glass plates on either side of the gel.

31. Apparatus for DNA sequencing comprising:

means for applying opposite polarity electrical potentials to a first and at least a second buffer;

means for applying fluorescently marked DNA strands to a plurality of channels of gel, whereby said fluorescently marked DNA strands are electrophoresed along said gel so that the bands of more mobile strands in at least one channel are fully resolved while some of the less mobile strands to be later formed into bands are unresolved in a continuous process;

means for focusing a microscope wherein the focus point of the microscope is within the gel during a scan;

means for scanning across said channels with light emitted from a laser and with said microscope; and

means for detecting fluorescent light emitted by said fluorescently marked strands, whereby the time sequence of separated bands may be obtained;

the means for focusing including means for focusing at one location;

moving the microscope along a scan to another location; and

adjusting the distance between the microscope and the gel so that the microscope is focused on the gel during at least a portion of a scan.

32. Apparatus for DNA sequencing comprising:

means for applying opposite polarity electrical potentials to a first and at least a second buffer;

means for applying fluorescently marked DNA strands to a plurality of channels Of gel, whereby said fluorescently marked DNA strands are electrophoresed along said gel so that the bands of more mobile strands in at least one channel are fully resolved while some of the less mobile strands to be later formed into bands are unresolved in a continuous process;

means for focusing a microscope wherein the focus point of the microscope is within the gel during a scan;

means for scanning across said channels with light emitted from a laser and with said microscope; and

means for detecting fluorescent light emitted by said fluorescently marked strands, whereby the time sequence of separated bands may be obtained;

means for transmitting intensity data to a cathode ray tube so that the intensity data extends substantially across a horizontal sweep of the cathode ray tube;

means for modulating an electron gun of the cathode ray tube with said intensity data; and

means for spacing said horizontal sweeps vertically to present a plurality of bands.