What you need to review for Final Lab Practical

Test tubes and flasks

As you know, you take your Final Lab Practical next week (12/6/16-12/9/16). Below is a list of things compiled by our teaching staff that you need to review, i.e., need to know for our Final Lab Practical. Please be aware that you do not get to use your lab manual when you take the Final Lab Practical, but you can use your calculator.

BIOL 135 Final Lab Practical Review
**GENERAL NOTE: The setup of the lab practical consists of various stations that test the hands-on skills you were taught throughout the semester. You correctly demonstrate these skills in order to do well on the practical final. If you are too slow at performing any of the assessments, it will be assumed that you did not learn the material, and thus will have points deducted and you will be moved to the next station.

LAB 1

  • Know “Basic Lab and Safety Procedures”
  • How to discard specific lab wastes
  • Specific examples to know:
  • 10 mL of acid → neutralize with water and pour down the drain with lots of water
  • Agar plate containing E.coli → tape closed and put in orange biohazard bag in biohazard bin
  • Test tube containing B.subtilus → goes to media prep to be autoclaved
  • Kimwipe used on pH meter → trash can
  • **TIP: a question may be asked that seems general, but BEWARE. If a question is general, such as how to dispose of a glove or Kimwipe that has something biological on them (cells, bacteria, etc.), then they need to be disposed of in biohazard bags, NOT in the trash. Be aware of what substance is on an object you are disposing because it makes a difference as to whether or not it goes in the trash, in a special trash container (like for cobalt chloride), or into the biohazard container (or the sharps container, or the broken glass box).

LAB 2

  • Using a beamed balance
  • Maximum capacity of our beamed balances ~ 610 g
  • Zeroing (taring) and using an electronic balance
  • Maximum capacity electronic balances ≤ 300.000 g
  • Know how to calibrate electronic balance using 200 g calibration weight
  • Measuring with a Vernier caliper
  • Measuring objects to the nearest 0.1 mm with a Vernier caliper. Helpful hint: first measure an object with a ruler to get an estimate of the linear dimension, and then measure with the Vernier Caliper for greater precision

LAB 3

  • Know the steps/stages/phases of mitosis and meiosis
  • Know the two alignments at metaphase I of meiosis
  • Be able to perform the various stages of mitosis and meiosis with pipe cleaners and beads, as done in lab

LAB 4

  • Serial dilutions
  • For example:
  • Make a 7-fold serial dilution in 4 beakers with the final volume contains 21 mL in the last beaker1 part solution + 6 parts diluent = 7 parts total21 mL / 7 fold = 3 mL stock solution poured from stock bottle and put in first beaker3 mL stock + 18 mL diluent; mix → 3 mL beaker 1 to beaker 2 + 18 mL diluent; mix → etc.
  • **TIP: Be sure to use a clean graduated pipet/pipet tip every time you transfer a liquid to avoid contamination/carry-over, and thus inaccurate dilutions.
  • Using a Pipetman along with checking the accuracy of a Pipetman.
  • With the plunger at the 1st stop, immerse the tip into the liquid and allow plunger to slowly return to the original position. When dispensing, push the plunger to the 1st stop before fulling pushing the plunger to the 2nd stop to dispense all fluid from the tip.
  • **TIP: Pay close attention to the different stop positions of the Pipetman, be sure to NOT let the plunger snap back to the original position (slowly release it by releasing thumb pressure), and make sure you know which Pipetman to use/how to set it to the correct volume/how to read the volume of each model of Pipetman. Not following these important points will result in point deductions.
  • Check the accuracy of a Pipetman: depending on the capacity of a Pipetman, tare a weigh boat on the electronic balance, set volume of Pipetman, load volume of water into tip, dispense water into weigh boat
  • Use the close approximation for the density of water that is 1 mL = 1000 μL = 1 g. Therefore, 100 μL = 0.1 g, 200 μL = 0.2 g, 1000 μL = 1 g. Depending on the model of Pipetman, one of these volumes will be good to check the Pipetman’s accuracy.
  • If the weight of volume delivered by a Pipetman is > 1% of what it should be, then that Pipetman is not accurate and you thus need to adjust volume to be delivered to account for this inaccuracy, or the Pipetman needs to be serviced.

 

LABS 5, 6

  • Calibrating a pH meter, and how to measure the pH of a solution
  • Before measuring the pH of a solution using a pH meter, you should identify whether the solution is acidic or basic by using universal pH paper. DO NOT dip the strip of pH paper into a solution, use a clean Pasteur pipet to put a drop on the paper.
  • If you are preparing to measure an acid, use the pH 7 and pH 4 buffers to calibrate. For a base, use the pH 7 and pH 10 buffers.
  • First check to see that the stopper plug is slid open. Clean off the pH probe with electrode (it should be sitting in pH 4 buffer solution) with DI water in a wash bottle, allowing the rinse water to fall into a waste beaker. Gently wipe the pH probe with a Kimwipe. Place the pH probe into pH 7 buffer, and allow it to stabilize. Place the pH probe into pH 7 buffer, and allow it to stabilize. Press the STANDARDIZE button.Remove pH probe from the buffer solution and rinse the pH probe with DI water, and dry with a Kimwipe. Place the pH probe in the second buffer solution, either pH 4 or pH 10 buffer. Again, allow to stabilize then press the STANDARDIZE button. Rinse the pH probe with DI water, and dry with a Kimwipe. Place the pH probe in the solution and measure its pH. When finished, rinse the pH probe with DI water, and dry with a Kimwipe, the put the probe in pH 4 buffer for storage.
  • Buffer solution color-code: pH 4 = red, pH 7 = yellow, pH 10 = blue

LABS 7, 8, 9

  • Adjusting a spectrophotometer and measuring the absorbance of a solution.
  • Before beginning, be sure the Spec20 has been on (warmed up) for 20 minutes. Set the wavelength with the wavelength control knob, as well as set the filter position using the lever on the front. With the sample compartment cover closed and the sample compartment empty, use the power switch/zero control knob (left) to adjust the meter to read 0% Transmittance. Next, take your blank reference tube, wipe the outside with a Kimwipe, and place it in the sample compartment and close the lid. Use the Transmittance/Absorbance control knob (right) to set the percent Transmittance to 100%. Remove the blank reference tube. To measure the Absorbance or Transmittance of a sample, with the outside of cuvette tube it’s in, then put the sample tube in the sample compartment, completely close the sample compartment lid, then read the Absorbance or Transmittance.
  • For the digital spectrophotometers you need to use the buttons to the right of the display to switch between Transmittance and Absorbance.
  • **TIP: Remember to vortex solutions before reading their Absorbance or Transmittance to be sure the solution is “homogenous.” Remember cobalt chloride (CoCl2) is toxic, so wear gloves when handling it. Remember, wear gloves when doing the Bradford Assay to prevent proteins on your hands contaminating your solutions.

LAB 10

  • Here is an overview of the basic guidelines for sterile technique: wash your hands with soap and water before you start and when you finish, wipe down your work area with 70% ethanol before you start and when you finish, set up your work area to minimize contamination, use sterile glassware, wear gloves if instructed, hold the opening of flasks, test tubes, or bottles at a 45° angle to minimize airborne contamination, and place a cap on a clean surface on the lab bench.
  • Sterile technique using graduated pipets, and when pouring solutions
  • **TIPS: Never allow the tip of a graduated pipet touch you or a surface. Remember to pass the bottom third of the pipet through the flame for 1-3 seconds BEFORE and AFTER loading/dispensing liquid microbial culture. All metal containers containing graduated pipets must be flamed before being uncapped and exposed to the air to reduce contamination.
  • Streaking an agar plate using sterile technique, and single colony isolation
  • **TIPS: Review the diagram in your manual for how to streak for single colony isolation. Be sure to fully flame an inoculation loop by holding it at the top of the blue flame cone and waiting until it turns bright red; this must be done for 2/3 of the tungsten wire with look, not just the loop end. After flaming a loop, be sure to allow the loop to cool (if picking up bacteria from a liquid culture) or cool it in “side agar” (if picking up from a solid culture) to avoid killing (frying) the bacteria. Always flame the inoculation loop BEFORE picking up bacteria and AFTER spreading it on the agar. Just lift the lid of an agar plate a bit (about 1-2 inches) when picking up bacteria or streaking.
  • Inoculating a liquid culture
  • First, flame the inoculation loop. Cool it by using a “side agar cooling spot,” before scooping up solid bacteria from an agar plate. For the broth, uncap the test tube and flame its opening. Be careful not to touch the inner sides of the test tube, then lower the cooled inoculation loop into the broth and give a few quick motions to “stir” the culture. Remove the loop. Flame the test tube opening and recap. Finish by flaming the inoculation loop.
  • Light microscope
  • Know all the parts to a light microscope
  • How to focus on a specimen. Begin by observing a specimen at the lowest power objective (4x) and increase as necessary
  • How to maximize resolution using Koehler Illumination
  • When to and not to use immersion oil. Remember, immersion oil is ONLY used with the 100x objective.
  • How to clean the lenses of a light microscope. Lens paper is the only material used to clean a microscope eyepiece and objective lenses, NEVER Kimwipes.

LAB 11

  • Preparing bacterial smears using liquid and solid cultures
  • To prepare a smear from an agar culture, put a very small drop of RO water on the center of the slide. Using sterile technique, remove a small amount of bacteria from an agar culture using an inoculation loop, then mix and spread the bacteria in the water droplet on the microscope slide. Remember with an agar culture, it takes a very little “scoop” of bacteria to give a usable smear.
  • To prepare a smear from a liquid culture of bacteria, do not place a drop of RO water on the slide, instead use sterile technique to remove a drop of liquid culture with an inoculation loop, then use the loop with the drop of culture to smear the bacteria onto the cleaned slide.
  • Allow the smear to air-dry completely. Once dry, quickly pass the slide through the flame three quick times to affix the bacteria to the slide. Once cooled, the bacterial smear is ready to stain.
  • Staining bacterial smears using methylene blue and gram staining techniques.
  • Methylene blue stain: apply methylene blue stain on the smear on a slide, a drop at a time until the smear is covered with stain. Allow the stain to sit on the smear for 60 seconds. If it begins to dry, add more stain. After 60 seconds gently wash off the stain with RO water. Remove excess water from the slide by using Kimwipes or paper towel. Use spray fixative on the moist stained smears and let dry for a couple minutes before examining with a microscope.
  • Gram stain: Flood a slide with crystal violet for 60 seconds. Pour off the stain and gently wash with RO water. Next, flood the slide with iodine solution and leave for 30 seconds to 1 minutes. Poor off and wash. While holding the slide at an angle, apply 95% ethanol one drop at a time until the violet color no longer appears in the runoff. Quickly rinse off the alcohol with water and blot dry. Counter stain by flooding the slide with safranine for 60 seconds. Pour off and wash. Blot dry as previously described and use spray fixative on moist stained smear before examining bacteria.

LAB 12

  • Direct methods used to measure bacterial growth:
  • Viable plate counts
  • Spread plate method: a volume of an appropriately diluted bacterial culture is spread over the surface of an agar plate using a sterile glass cell spreader (aka hockey stick). Allow the bacterial culture to soak into the agar for ~15 minutes before inverting the agar plate and incubating.
  • **TIPS: Counts must be between 30 and 300 for both forms of direct methods. When sterilizing a glass cell spreader, first soak the spreader in ethanol then flame the spreader and allow all ethanol to burn off before using to spread the liquid culture evenly on the agar.
  • Indirect methods used to measure bacterial growth:
  • Turbidity measurements using Spec20

LAB 13

  • Calibrate eyepiece graticule using a stage micrometer.
  • To begin, focus on the scale on the stage micrometer. Next, align the lines of the eyepiece graticule with those of the stage micrometer so that they are parallel, by adjusting the stage micrometer or rotating the eyepiece with the graticule. Align the zero lines of the stage micrometer and eyepiece graticule. Count how many lines on the stage micrometer fit precisely in a given number of lines of the eyepiece graticule. From this record the value that represents how many graticule lines represent a designated length (with units) when using 10x, 40x or 100x objective.
  • For example:
  • If you counted 39 eyepiece graticule lines per 0.1 mm of the stage micrometer, then the distance between each eyepiece graticule line is 100 μm / 39 = 2.6 μm
  • Measure length of object using calibrate eyepiece graticule
  • Using the value you found that represents how many graticule lines represents a designated length, measure the length of an object on a slide
  • Examine and identify histological sections

About next week’s Lab 12 and material in Appendix 4 of your manual

As it says at the beginning of Lab 12 in your manual, the material covered in this lab assumes that you know what’s in Appendix 4 of your manual. You need to understand what’s covered in Appendix 4 on exponents, logarithms, and functions (especially exponential growth) to “do” Lab 12. And experience tells us that many of you need to review how to plot points on log-linear (semi-log) axes that’s covered at the very end of Appendix 4.

Bacterial cell size vs Eukaryotic cell size

In Lab 11 you will be characterizing bacteria, and in Lab 12 you will be measuring bacterial growth. Knowing about the difference in the size of bacteria (prokaryotes) and eukaryotic cells is relevant to both of these labs. Prokaryotic cells are small when compared to eukaryotic cells; prokaryotes are typically about 0.5 – 3 μm in diameter, and eukaryotic cells are typically about 10 – 20 μm in diameter.

The small size of prokaryotes, as compared to eukaryote cells affects a number of biological functions. For example, the rate prokaryotes take up nutrients into their interiors, and remove waste products out into the external environment through their plasma membrane can greatly affect their cellular metabolic rates and growth rates. In general, the cellular metabolic rate and growth rate of prokaryotes is much higher than the rates for eukaryotic cells. This difference is because transport rates are in part a function of the plasma membrane surface area available relative to the interior volume of the cell. Therefore, small cells with small volumes have more surface area relative to their volume than do large cells. Let’s illustrate this surface area to volume relationship with small and large spheres.

Below are the formulas for the surface area of a sphere, and for the volume of a sphere written as a ratio of surface area to the volume. As you can see, the formulas for surface area to volume expressed as a ratio simplify to 3 divided by the radius.
lab11_surface-area-to-vol
So, a 2 μm diameter (1 μm radius) spherical prokaryote will have a surface area to volume ratio of 3, but a 12 μm diameter (6 μm radius) spherical eukaryotic cell will have a surface area to volume ratio of 0.5, i.e., the small prokaryotic cell has more surface area to its volume than a large eukaryotic cell. Prokaryotes having more surface area for their volume facilitates a higher metabolic rate, as well as a shorter generation time (the time it takes for one cell to divide into two cells) than large eukaryotic cells with less surface area for their interior volume. In Lab 12 you will see just how fast E. coli in liquid culture divide when they have lots of nutrients and oxygen available.

Reminder about next week’s Lab 6

Reminder

Remember, for Lab 6 you need to write your flow charts and calculate the pH of the buffer you will make before you come to lab. If you lost your half-sheet of paper with this information for your section, here is the text on these half-sheets.

Measuring the pH of a buffer Addendum for Lab 6
As per the information at the beginning of Lab 6, here are the concentrations of acetic acid and sodium acetate you will use, and what you need to calculate the pH of this buffer (and record in your lab notes) before you come to Lab 6.

Sections 001, 002, 003, 004
0.2 M acetic acid
0.5 M sodium acetate

Sections 005, 006, 007, 008
0.5 M acetic acid
0.1 M sodium acetate

See your lab manual, and Lab 6 Prep Lecture for examples of how to do these calculations, and be sure to calculate the pH of the buffer for your lab section.

Reminder about next week’s Lab 5

Lab 5 reminder

Remember, for Lab 5 you need to write your flow charts and calculate the pH of the two weak acids and one weak base before you come to lab. If you lost your half-sheet of paper with the weak acids and base for your section, here is the text on these half-sheets.

Addendum for Lab 5
As per the information at the beginning of Lab 5, here are the weak acids and base you need for calculating (and recording in your lab notes) their pH for their given concentration before you come to Lab 5.

Sections 001, 002, 003, 004
0.005 M citric acid (pKa of 3.14)
0.0025 M lactic acid (pKa of 3.08)
0.0005 M ammonia (pKa of 9.25)

Sections 005, 006, 007, 008
0.01 M citric acid (pKa of 3.14)
0.015 M lactic acid (pKa of 3.08)
0.0025 M ammonia (pKa of 9.25

See your lab manual for examples of how to do these calculations.

Reminder about next week’s Lab 4

String on finger to remember something
Remember, for Lab 4 you need to use the “Handout for Lab 4 Exercises” you received for your lab section number during this week’s Lab 3 to write your flow charts/diagrams with all their calculations on your Lab 4 notes pages for all the exercises on both sides of the handout. You need to have all these flow charts/diagrams with their calculations done before you come to your lab section next week.

Lab 3 mitosis & meiosis simulations; t-tests and chi-squared tests

Mitosis and meiosis simulations

pipe cleaners+beads
You left lab 2 with a plastic bag with pipe cleaners and beads so you could practice simulating mitosis and meiosis before you come to lab 3. Remember, you need to bring your pipe cleaners and beads in their bag back with you to lab 3. For your information, we recycle these pipe cleaners and beads for use next semester.

mitosis

Above is a diagram of mitosis (click on image to see it bigger). At the top is the key to identifying the maternal and paternal chromosomes of this somatic cell undergoing mitosis. At the left is the cell in interphase. As you know, during interphase the DNA of the chromosomes replicate. So when the cell enters prophase each chromosome has a two part structure consisting of sister chromatids joined by a centromere. At metaphase, the chromosomes randomly align at the metaphase plate perpendicular to the spindle. Also at metaphase the centromeres duplicate. At anaphase, the sister chromatids are pulled to opposite poles of the cell by the spindle fibers. The separated sets of chromosomes become enclosed in a nuclear membrane at telophase. Cytokinesis will complete the mitotic division. The two cells that are the result of this mitotic division are genetically identical to the original cell at the left.

Incidentally, your bag of pipe cleaners and beads has two different colored pipe cleaners to represent maternal and paternal chromosomes (and their sister chromatids), and it has extra beads so you can simulate the centromeres duplicating in both mitosis and meiosis.

Below is a stop motion animation of the mitosis simulation like you will do in lab 3.

(Direct link to YouTube video.)

Meiosis, alignment 1, parental

The diagram above shows 1 of 2 alignments of homologous chromosomes at metaphase 1 of meiosis (click on image to see it bigger). Again, at the top is the color code for the maternal and paternal chromosomes of this germ cell undergoing meiosis. Please note that in this diagram of meiosis, there is no crossing over of sister chromatids. At the left is a germ cell in interphase, where it replicates its DNA, such that when this germ cell enters prophase 1, each chromosome has a two part structure consisting of sister chromatids joined by a centromere. At metaphase 1 of meiosis, homologous chromosomes pair and align at the metaphase plate in an alignment that determines the maternal and paternal chromosome complement of the resulting gametes. Following metaphase 1, is anaphase 1, and the maternal chromosomes go to one pole of the dividing germ cell, and the paternal chromosomes go to the other pole. Following telophase 1, the two meiotic products progress through prophase 2, metaphase 2, and anaphase 2. It is important to point out that there is no DNA replication between telophase 1, and prophase 2 of meiosis.

Carefully compare the alignment of maternal and paternal homologous chromosomes at metaphase 1, and the maternal and paternal chromosome complement of the resulting gametes. We call these resulting gametes, parental gametes. Below is a stop motion animation showing you how to simulate meiosis for “alignment 1″ and paternal gametes.

(Direct link to YouTube video.)

Meiosis, recombinant, alignment 2

The diagram above illustrates alignment 2 of homologous chromosomes at metaphase 1 of meiosis, and recombinant gametes (click on image to see it bigger). At the left is the germ cell in interphase where it replicates its DNA, such that when this germ cell enters prophase 1, each chromosome has a two part structure consisting of sister chromatids joined by a centromere. Again, at metaphase 1 of meiosis, the homologous chromosomes pair, and align at the metaphase plate in an alignment that, again, determines the maternal and paternal chromosome complement of the resulting gametes. Be sure to note that this alignment 2 is different from the alignment 1.

Again, there is a correlation between the alignment of maternal and paternal homologous chromosomes at metaphase 1, and the maternal and paternal chromosome complement of the resulting gametes; we call these resulting gametes, recombinant gametes. Below is a stop motion animation showing you how to simulate meiosis for “alignment 2″ and recombinant gametes.

(Direct link to YouTube video.)

So why are these two different alignments at metaphase I of meiosis so important? The genetic makeup of the gametes formed depends in a large part on the alignment of maternal and paternal chromosomes at metaphase I of meiosis, and it’s random as to how the chromosomes align at metaphase I of meiosis. Furthermore, when two gametes come together at fertilization, the genetic makeup of an offspring is set, and the coming together of gametes is a random event as well.

Try to do t-tests with data collected in Lab 2 before come to Lab 3

Since you have your data from Lab 2, you can write out your flow chart for the t-tests in your Lab 3 notes before you come to Lab 3, then do (or attempt to do) your t-tests in your Lab 3 notes (after your t-test flow charts). Doing so saves you time during Lab 3, and gives you the opportunity to correct any mistakes you may have made, plus get out early or on time.
t-test equations, etc.

Preview of chi-squared tests you do in Lab 3

In Lab 3 you will count the phenotypes of the progeny from different parental corn monohybrid or dihybrid crosses. Once you have these counts, then you do χ2 tests to determine the genotypes of the parents of each cross.

You received a handout for Lab 3 during Lab 2 with all the genotypes and phenotypes of monohybrid and dihybrid corn crosses you will see in Lab 3. You count the frequency of phenotypes of offspring of these crosses. For example, there will be flats of corn seedlings from a monohybrid cross with a seedling height gene (the wild-type tall allele T, and the recessive dwarf t allele; T/T or T/t = tall height, and t/t = dwarf or stunted height). Here’s a labeled photo illustrating these two seedling phenotypes.

To illustrate how you do χ2 tests, let’s say for a monohybrid cross with the seedling height gene described above you count 46 wild-type tall seedlings, and 56 dwarf seedlings. The first thing you want to do is set up an observed and expected phenotype table like the one below.

  wild-type tall dwarf Total
Observed phenotype 46 56 102
Expected phenotype      

As you can see, the “expected” cells in the table above are empty right now. This is because we have to first decide what genetic cross are we going to do a χ2 test. First, you want to note that there are offspring with two different phenotypes from this monohybrid cross, tall and dwarf. Now what are the genotypes of parents that would give tall and dwarf offspring, and what would be the phenotypic frequency of offspring? One of two crosses would be T/t × T/t ⇒ 3 tall : 1 dwarf, and the other would be T/t × t/t ⇒ 1 tall : 1 dwarf. (Note, while there are other parental crosses for this allele, these two are the only ones to give tall and dwarf offspring.) We need to do a χ2 test for each of these two possible parental crosses to be sure of our results. So, we test whether our offspring counts come from a parental cross of T/t × T/t. The first thing we need to do is to complete the table above with our expected frequency for a total of 104 offspring for this cross of T/t × T/t ⇒ 3 tall : 1 dwarf offspring, as shown below.

  wild-type tall dwarf Total
Observed phenotype 46 56 102
Expected phenotype 76.5 (i.e., 76 or 77) 25.5 (i.e., 26 or 25) 102

Now we state our H0 and Ha hypotheses. H0 is that our observed frequency does not differ from the expected frequency for a parental cross of T/t × T/t. Ha is that our observed frequency differs from the expected frequency for a parental cross of T/t × T/t. Next we use the equation for calculating χ2.

As stated in Lab 3 of your manual, we’ll be using an α = 0.05, and as described in Lab 3, the df = 1 for this χ2 test. So we use the Critical Values of the χ2 Distribution at the back of your manual, and we find that χ2calculated ≥ χ2critical. Thus we reject our H0 that our observed frequency does not differ from the expected frequency, i.e., it’s unlikely that the parental cross was T/t × T/t.

Next we test whether our offspring counts come from a parental cross of T/t × t/t ⇒ 1 tall : 1 dwarf, going through the same steps as above.

  wild-type tall dwarf Total
Observed phenotype 46 56 102
Expected phenotype 51 51 102

Our H0 and Ha hypotheses for this χ2 test are: H0 is that our observed frequency does not differ from the expected frequency for a parental cross of T/t × t/t. Ha is that our observed frequency differs from the expected frequency for a parental cross of T/t × t/t. Here is the equation for calculating this χ2.

Here we find that χ2calculated < χ2critical. Thus we accept our H0 that our observed frequency does not differ from the expected frequency, i.e., there’s a 95% probability that the parental cross was T/t × t/t.

Here are some labeled photos to show you the phenotypes of corn kernels and other corn seedlings from monohybrid and dihybrid crosses you will see in Lab 3. Plus there are counts you can use to practice doing more χ2 tests.

corn seedlings from dihybrid cross
Corn seedling phenotypes from a dihybrid cross for seedling height and chlorophyll alleles (T and t alleles same as for monohybrid cross above; wild-type chlorophyll allele, A gives green leaves, mutant recessive albino allele, a gives white (no chlorophyll) leaves.
corn kernels for monohybrid cross
Corn kernel phenotypes from a monohybrid cross for seed color (the wild-type purple color, P, and the recessive mutant white color, p).
corn kernels from a dihybrid cross
Corn kernel phenotypes from a dihybrid cross for the two alleles: C, wild-type purple kernel, c, mutant recessive white kernel; Su, wild-type flint kernel, su, mutant recessive sweet kernel.

Sample corn kernel/seed counts
Monohybrid cross counts (observed numbers)
purple = 300 kernels
white = 98 kernels

Dihybrid cross counts (observed numbers)
purple flint = 123 kernels
purple sweet = 41 kernels
white flint = 30 kernels
white sweet = 12

Sample corn seedling counts
Another monohybrid cross counts (observed numbers)
tall = 82 seedlings
dwarf = 28 seedlings

Dihybrid cross counts (observed numbers)
tall green = 61 seedlings
dwarf green = 19 seedlings
tall albino = 16 seedlings
dwarf albino = 6 seedlings

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