TA Conference 2

BIOL-202: Basic Genetics Notes

TA Conference Information

  • Course: BIOL-202: Basic Genetics

  • TA Name: Eric Johannessen

  • Email Contact: eric.wootton@mail.mcgill.ca

Weekly Conferences

  • Frequency: TA-led conferences are held weekly.

  • Attendance: Optional, but highly recommended.

  • Flexibility: You can attend any session or any number of sessions each week.

  • Schedule:

    • Monday: 13:00-14:30, Room STBIO N5/1, TA: Kate

    • Tuesday: 11:30-13:00, Room STBIO S3/4, TA: Eric

    • Wednesday: 14:30-16:00, Room STBIO S3/4, TA: Justin

    • Wednesday: 16:30-18:00, Room STBIO N5/1, TA: Arghya

    • Thursday: 10:00-11:30, Room STBIO S3/4, TA: Leylia

Conference Structure

  • Purpose: Intended for solutions to weekly practice problems and general Q&A sessions.

  • Benefits:

    • Opportunity to receive solutions to practice problems.

    • Chance to get questions answered by the TA.

    • Conferences are designed to prepare students for course assessments effectively.

Week 2: Practical Questions and Analysis

Question 1

  • Scenario: The F1 dihybrid pea plants from a cross exhibit round, yellow seeds.

  • Testcross Results Reported by Prof Moon:

    • Round, yellow: 40

    • Round, green: 260

    • Wrinkled, yellow: 285

    • Wrinkled, green: 32

Part (a): Parental Types

  • Outcome:

    • Most likely parental types: Round green and wrinkled yellow.

  • Reasoning:

    • These phenotypes are significantly higher in frequency compared to others.

    • The deviation from the expected 1:1:1:1 ratio (predicted by independent assortment) indicates that two genes are likely linked on the same chromosome.

    • Parental combinations are generally more common in genetic crosses than recombinant types.

Part (b): Convincing Prof Moon

  • To prove results deserve an A, you must compare your own testcross results with Prof Moon's findings.

  • **Yours:

    • Round, yellow: 40

    • Round, green: 138

    • Wrinkled, yellow: 145

    • Wrinkled, green: 25**

  • Prof Moon’s Results:

    • Round, yellow: 40

    • Round, green: 260

    • Wrinkled, yellow: 285

    • Wrinkled, green: 32

Step 1: Ratio Calculation

  • Prof Moon's Total Progeny: 617

  • Your Total Progeny: 338

  • Ratios calculated as follows:

    • Round yellow: 40/617

    • Round green: 260/617

    • Wrinkled yellow: 285/617

    • Wrinkled green: 32/617

  • Apply proportions in comparison to your results to derive your results in relation to totals.

Chi-Squared Calculation

  • Formula for Chi-squared:
    χ2=∑(O<em>i−E</em>i)2Ei\chi^2 = \sum \frac{(O<em>i - E</em>i)²}{E_i}

  • Observed (O) vs. Expected (E) results as follows:

    • Round, yellow: 30 (O), 21.91 (E)

    • O - E = 8.09

    • (O - E)² = 65.45

    • Round, green: 138 (O), 142.43 (E)

    • O - E = -4.43

    • (O - E)² = 19.62

    • Wrinkled, yellow: 145 (O), 156.13 (E)

    • O - E = -11.13

    • (O - E)² = 123.88

    • Wrinkled, green: 25 (O), 17.53 (E)

    • O - E = 7.47

    • (O - E)² = 55.80

  • Sum of Chi-squared results:
    χ2=7.1\chi^2 = 7.1

  • Critical Value: 7.1

  • Degrees of Freedom: 3 (4-1)

Statistical Significance

  • p-value: Falls between 0.05 and 1, indicating that results do not allow for the rejection of the hypothesis.

  • Conclusion: The data suggests that your results are statistically similar to Prof Moon's.

Week 2: Question 2

Question 2
Part (a): Cross between Drosophila Mutant Flies

  • Genetics Context: Two genes located on the second chromosome:

    • Gene (o) responsible for brown pigment production.

    • Gene (s) responsible for wing growth.

  • Phenotypes of Loss-of-function alleles:

    • Loss-of-function for o: Orange body color.

    • Loss-of-function for s: Shorter wings.

  • Cross Scenario:

  • Cross: oo . SS x OO . ss

  • F1 Resulting Genotype and Phenotype:

    • Genotype: Oo . Ss

    • Phenotype: Wild-type (normal appearance).

Part (b): Calculating Wild-type F2 Expectations

  • Recombination Distance: Between genes o and s is identified as 14 cM (centimorgans).

  • Selfing F1s:

    • F1s are selfed: Oo . Ss x Oo . Ss

  • The expected gamete frequency calculations consider a 14 cM distance leading to recombinant and parental types:

  • Gamete Frequencies from Female and Male:

    • O . S: 7% (Recombinant)

    • O . s: 43% (Parental)

    • o . S: 43% (Parental)

    • o . s: 7% (Recombinant)

Wild-type Combinations

  • Combinations for Wild-type Outcome:

    • From O.S (7% from female) x O.S (7% from male) = 0.49%

    • Other recombinations yield various probabilities based on either parental or recombinant types being combined.

  • Total Wild-type Fraction of F2s:

  • Calculation yields approximately 50.49% of the F2s will exhibit a wild-type phenotype.