Category: My Classroom Material

Campbell Problem 6

Molecular Genetics Problem 6
6. A space probe discovers a planet inhabited by creatures who reproduce with the same hereditary patterns as those in humans. Three phenotypic characters are height (T = tall, t = dwarf), hearing appendages (A = antennae, a = no antennae), and nose morphology (S = upturned snout, s = downturned snout). Since the creatures were not “intelligent” Earth scientists were able to do some controlled breeding experiments, using various heterozygotes in testcrosses. For a tall heterozygote with antennae, the offspring were tall-antennae, 46; dwarf-antennae 7; dwarf-no antennae 42; tall-no antennae 5. For a heterozygote with antennae and an upturned snout, the offspring were antennae-upturned snout 47; antennae-downturned snout, 2; no antennae-downturned snout, 48: no antennae-upturned snout 3. Calculate the recombination frequencies for both experiments.

Experiment 1 (Frequency/Distance between T and A).

Determine the recombination frequency for the genes controlling Tallness and Antennae:

46 tall-antennae = 46% expected
42 dwarf-no antennae = 42% expected
7 dwarf-antennae = 7% recombinant
5 tall-no antennae = 5% recombinant

Total = 100

Therefore this recombination frequency between genes T and A is 12%

Experiment 2. (Frequency/Distance between A and S)

Determine the recombination frequency for the genes controlling Antennae and Snout:

47 antennae-upturned snout = 47% expected
48 no antennae-downturned snout = 48% expected
2 antennae-downturned snout = 2% recombinant
3 no antennae-upturned snout = 3% recombinant

Total = 100

Therefore this recombination frequency between genes A and S is 5%

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Campbell Problem 8

Molecular Genetics Problem 8
8. Imagine that a geneticist has identified two disorders that appear to be caused by the same chromosomal defect and are affected by genomic imprinting: blindness and numbness of the limbs. A blind woman (whose mother suffered from numbness) has four children, two of whom, a son and daughter, have inherited the chromosomal defect. If this defect works like Prader-Willi and Angelman syndromes, what disorders do this son and daughter display? What disorders would be seen in their sons and daughters?

In Prader-Willi and Angelman syndromes the type of symptom exhibited in the offspring depends upon which parent contributes the defective chromosome.

In this case children receiving a defective chromosome from the father will suffer from numbness and children receiving a defective chromosome from the mother will be blind.

The pedigree below helps to sort out how the imprinting works.

 

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Campbell Problem 9

Molecular Genetics Problem 9
9. What pattern of inheritance would lead a geneticist to suspect that an inherited disorder of cell metabolism is due to a defective mitochondrial gene?

 

The disorder would always be inherited from the mother because the mother’s mitochondrial gene is the only one that survives when the zygote is formed. The gamete from the mother contains all the information. The head of the father’s sperm is the only part that survives during fertilization. The tail of the sperm containing the male’s mitochondria (an their genes) is lost when the zygote begins development. Thus it is only from the mother that the disorder can be inherited.

 

Do Brain Cells Run Out of Gas?
Within each cell reside hundreds of tiny gas stations known as mitochondria. These essential organelles generate a large share of the fuel, a molecule called ATP, that cells use to power their biological machinery. There’s a suspicion, admittedly controversial, that problems with these energy-supplying mitochondria contribute to the progression of age-related neurodegenerative illnesses such as Alzheimer’s, Parkinson’s, and Huntington’s diseases, says Douglas C. Wallace of Emory University School of Medicine in Atlanta. In 1993, Wallace and his colleagues reported on comparisons of the mitochondrial DNA of Alzheimer’s patients and that of people without Alzheimer’s, who served as controls. This genetic material, which contains all the instructions necessary for mitochondria to function and replicate, is independent of the DNA found in a cell’s nucleus. Wallace’s group discovered that a particular mutation in mitochondrial DNA showed up in more than 5 percent of Alzheimer’s patients but in less than 1 percent of a random group of people with-out the disease. Studies on animals support the importance of mitochondria in brain disorders. When investigators destroy mitochondria or inhibit the activity of enzymes crucial to mitochondrial function in rats or mice, the rodents develop behavioral or physical attributes of Alzheimer’s, Huntington’s, and Parkinson’s diseases. &emdash; J. Travis

Science News: Aug. 5 • Vol. 148, No. 6

 

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Carbon Dioxide Use in Plants

 

 

Do Plants Consume or Release CO2?

 

Introduction

The rate of photosynthesis can be determined by measuring the rate of production of sugar or oxygen or by measuring the rate of decrease in carbon dioxide concentration. A common aquarium plant called, Elodea,  can be used to show fast carbon dioxide is being removed from the water in which the Elodea is submerged.

6CO2 + 12H2O + light energy —> C6H12O6 + 6O2 + 6H2O

 

In this lab, you will use phenol red as an indicator to show whether CO2 is being consumed or produced in a reaction. It is well known that in the presence of light, plants perform photosynthesis. At the same time, plants are also performing cell respiration. To demonstrate this, we will determine whether CO2 is consumed or produced as Elodea is placed in either a light or dark environment. The change in CO2 will be detected by the pH indicator phenol red. Phenol red is yellow under acidic conditions (high H+ ion concentration), pink to magenta under basic or alkaline conditions (low H+ ion concentration), and orange under neutral conditions. A change in the amount of CO2 will cause a directly proportional change in H+ ion.

If the CO2 concentration decreases, the H+ ion concentration will also decrease, and the solution will change to pink, becoming basic.

If the CO2 concentration increases, the H+ ion concentration will also increase, and the solution will change to yellow, becoming acidic.

Neutral solutions of phenol red will be orange.

Materials:

phenol red solution,  4 sprigs of Elodea, soda straw, 4 test tubes, labeling marker, 100 ml graduated cylinder, beaker, aluminum foil

Procedure:

  1. Create a solution of phenol red by adding concentrated phenol red to about 100 ml of water in a beaker. The phenol red may change color as a result of adding water (depending on how acidic your tap water is). Your goal is to make your solution a neutral orange color. You can do this by gently blowing into the solution with a straw.
  2. Label 4 test tubes 1, 2, 3, and 4.
  3. Once you have the solution at an orange color, transfer it to 4 test tubes (they should be filled about 2/3 full with your orange solution).
  4. Place a cut piece of Elodea (cut end up) into tubes 2 and 4 and tightly cap.
  5. Test tubes 3 and 4 will not have Elodea. Cap and then cover these tubes with aluminum foil so no light can enter.
  6. Place tubes 1 and 2 in bright light.
  7. Place tubes 2 and 4 in the dark.
  8. After 24 hours, uncover and examine all 4 test tubes and record the results.

Data:

 

Test Tube # Contents of Tube Initial Color Final Color
1
2
3
4

 

Conclusion:

1. What test tubes served as the controls in this experiment. Why?

 

 

2. What was the dependent variable?

 

3. Do you think there would have been any change in any of the test tubes if they were left for 48 or 72 hours? Explain.

 

 

4. Describe and explain what happened in the test tubes.

 

 

 

5. Why did the color change occur?

 

6. Where does the carbon dioxide that is removed from the solution go?

 

7. What other process goes on in plant cells that requires oxygen and produces carbon dioxide?

 

8. What was the purpose in tightly capping all four test tubes?