QUESTION 1 Background Information

In this practical, the focus is on studying the combinations of alleles in a monohybrid cross through model representation. Alleles typically occur in pairs, with one allele being dominant over the other. In the context of gametes, only one allele from each pair is present in the meiosis process. When both the dominant and recessive alleles are present in the offspring, the dominant allele dictates the phenotype observed.

The Central Question

The question being explored is: "Can we predict the outcome of monohybrid crosses between parents with different allele combinations?"

Hypothesis

The hypothesis posits that if the allele combinations of the parents are known, the ratio of the F1-generation can be determined.

Materials Required
  • 20 red beads
  • 20 white beads
  • 5 beakers

Method – INVESTIGATION A

  1. Arrange three beakers next to each other on the table.
  2. Add 20 red beads to the first beaker.
  3. Add 20 white beads to the second beaker.
  4. Blindly select one bead from the first beaker and one from the second beaker.
  5. Transfer both selected beads to the third beaker.
  6. Continue steps 4 and 5 until all beads from the first and second beakers are utilized.
  7. Record the count of red and white beads in the third beaker, which represents the F1-generation, in the designated area below:
       - Amount of red beads in beaker 3: _________
       - Amount of white beads in beaker 3: _________
       - Red-White Parents

Method - INVESTIGATION B

  1. Arrange four beakers next to one another on the table.
  2. Add 20 red beads to the first beaker.
  3. Add 10 red beads and 10 white beads to the second beaker, mixing them thoroughly.
  4. Blindly select one bead from the first beaker and one from the second beaker.
  5. Examine the beads in hand:
       - If both beads are red, place them in the third beaker.
       - If one bead is red and the other is white, place them in the fourth beaker.
       - The contents of beaker 3 and 4 illustrate the potential allele combinations in the offspring.
  6. Repeat steps 4 and 5 until depleting the beads.
  7. Record the quantities in beakers 3 and 4 and compute the ratio of beads in beaker 3 and 4 (the F1-generation):
       - Amount of red beads in beaker 3: __________
       - Amount of red and white beads in beaker 4: __________
       - Ratio of red : red-white beads = ________ : _________
       - Red-White Red Parents 1

Method - INVESTIGATION C

  1. Position five beakers next to one another on the table.
  2. Add 10 red beads and 10 white beads into the first and second beakers respectively.
  3. Mix the contents of each beaker thoroughly.
  4. Blindly select one bead from beaker 1 and one from beaker 2.
  5. Assess the selected beads:
       - If both are red, place them in beaker 3.
       - If one is white and one is red, place them in beaker 4.
       - If both are white, transfer them to beaker 5.
  6. Repeat steps 4 and 5 until all beads are utilized.
  7. Document the amounts in beakers 3, 4, and 5 and calculate the ratio of beads in these beakers (the F1-generation):
       - Amount of red beads in beaker 3: __________
       - Amount of red and white beads in beaker 4: __________
       - Amount of white beads in beaker 5: __________
       - Ratio of red : red-white : white beads = _____ : _____ : ____
       - 5 White Red-White Red Parents 2

Answer the Following Questions

  1. Identify the independent and dependent variables in the investigation:
       - Independent variable: ______________________________________________
       - Dependent variable: _____________________________________________
  2. Red beads are dominant over white ones. Use the letters R (red) and r (white) to fill in the genotypes in the following table. Then complete the table by populating the amount of each genotype of the F1-generation as determined by the three investigations:
       - GENOTYPES OF THE F1-GENERATION OF THE DIFFERENT INVESTIGATIONS A TO C
       - Bead combinations
          - Red
          - Red-white
          - White
       - Genotypes
          - 3.1.1.
          - 3.1.2.
          - 3.1.3.
          - Investigation A
          - 3.1.4.
          - -
          - Investigation B
          - 3.1.5.
          - 3.1.6.
          - -
          - Investigation C
          - 3.1.7.
          - 3.1.8.
          - 3.1.9.
  3. Utilize the data in the table to produce a column graph representing the resulting F1-generations from your three investigations. Use the space provided below:
  4. Elucidate the relationship between the dependent and independent variable for each investigation. HINT: Use the terms homozygous and heterozygous.
       - Investigation A: (6)
       - TOTAL QUESTION 1: [20]
       - Investigation B:
       - Investigation C:

QUESTION 2

  1. In a family with brown (dominant) and blue (recessive) eyes:
       - Parents: Anrie (brown eyes) and Johan (brown eyes). Children: Susan (brown eyes), Rory (brown eyes), Janet (blue eyes) and Liam (brown eyes). Notably, Liam tragically died in a car accident at age 15.
       - Susan marries Martin (also with brown eyes and no family history of blue eyes). They have two daughters, both with brown eyes.
       - Rory marries Lelani (brown eyes), they have two sons (both with brown eyes) and one daughter (blue eyes).
       - Janet moves to England with her husband Dean (blue eyes). They have one child whose sex is currently unknown.
       - Create a complete pedigree diagram with appropriate symbols, ensuring all genotypes and phenotypes (with a key) are included along with the potential genotype of Janet and Dean’s child.
  2. The grading allocation for the pedigree diagram includes elements like:
       - Correct symbol for Liam - 1 0
       - Correct symbol for unknown child - 1 0
       - Genotypes included - 1 0
       - Genotype of unknown child - 2 0
       - Phenotypes with a key - 2 0
       - Diagram must be appropriately drawn (lines, levels, etc.) - 1 0
       - All sexes must be documented correctly - 2 0
       - All genotypes must be accurate - 4
       - Gene allocation: 1 – 2 incorrect genotypes - 3, 3 – 4 incorrect genotypes - 2, 5 – 6 incorrect genotypes - 1, More than 6 incorrect genotypes - 0
       - TOTAL = 14 marks

Genotypes Analysis

  1. When evaluating a woman for the potential father of her child via blood tests, we consider:
       - The woman possesses blood group O, while the two possible fathers have blood groups: Male 1 - AB and Male 2 - B. The tests confirm Male 2 as the biological father of the child with blood group O.
       - Using Punnett squares elucidates why Male 2 is the biological father while Male 1 is eliminated from consideration:
          - Test cross 1:
       - MAN 1 with woman
          - Gametes: IA, IB, i
          - Resulting Genotypes: IAi, IBi
          - Conclusion: Male 1 (blood group AB) cannot be the father, as these genotype combinations do not yield offspring with blood group O.
       - Test cross 2:
       - MAN 2 with woman
          - Gametes: IB, i
          - Resulting Genotypes: IBi, ii
          - Conclusion: Male 2 (blood group B) could indeed be the father, with a 50% chance that the offspring would have blood group O if his genotype is IBi.
       - TOTAL QUESTION 2: [20]
       - GRAND TOTAL: [50]
       - GRADE 12 TERM 2 PRACTICAL TOTAL: 40 MARKS
       - GENETICS AND HEREDITY - MEMORANDUM