TA Conference #1

Course Title: BIOL-202: Basic Genetics
TA Conference Schedule
- Conferences are held weekly
- Attendance: Optional but strongly encouraged
- Flexibility: Students can attend any session or multiple sessions each week

Conference Times
- Monday: 13:00 - 14:30, STBIO S3/4, TA: Ryan
- Tuesday: 14:30 - 16:00, STBIO S3/4, TA: Eric
- Wednesday: 10:00 - 11:30, STBIO S3/4, TA: Lauren
- Thursday: 11:30 - 13:00, STBIO S3/4, TA: Andy
- Friday: 13:30 - 15:00, STBIO S3/3, TA: Arghya

Solutions to Weekly Practice Problems
General Q&A
- Purpose: To provide solutions to weekly problems and answer student inquiries.
- Advantage: Attending will enhance preparedness for course assessments.

Discussion Board:
- Students are encouraged to post questions on the discussion board rather than emailing TAs directly.
- Benefits:
- If a student has a question, it is likely others do too, allowing collective benefit from answers.
- Many questions might already have an answer posted.

Scenario: Cleft Chin - Observed in Kirk and Michael Douglas (grandfather and father), but not in the youngest Douglas.
- Question 1 (a): Is this a dominant or recessive trait? Draw the pedigree.

Observations of Generations:
1. Grandfather has a cleft chin.
2. Father has a cleft chin.
3. Grandson does not have a cleft chin.
Typical Autosomal Dominant Pattern:
- In a dominant trait, if a parent expresses the trait, they have at least a 50% probability of transmitting it to offspring, assuming they are heterozygous.
- The father's ability to produce a child without the cleft chin indicates he is likely heterozygous (one dominant and one recessive allele).
- The mother, presumed homozygous recessive (no cleft chin, trait is rare), allows the potential for the child to inherit two recessive alleles, resulting in no cleft chin.
- Conclusion: Presence of one of the cleft chin alleles is sufficient for expression, indicating dominance of the trait.

Question 1 (b):
- Investigate the two hypotheses regarding the Biol202 gene's role in cleft chin development:
1. Hypothesis 1: Cleft chin produced by a loss-of-function mutation in Biol202.
2. Hypothesis 2: Cleft chin produced by a Biol202 allele exhibiting ten times stronger kinase activity than the wild type.

Biol202 Gene Characteristics:
- Haplosufficient Gene: Losing one copy doesn't lead to altered phenotype as the remaining functional copy suffices.
- Loss-of-function mutations typically yield recessive traits, requiring both alleles to be mutated for phenotype expression.
- In contrast, gain-of-function mutations can result in dominant phenotypes as one active allele can express the trait, overshadowing the normal allele.
Interpretation of Trait Observations:
- Cleft chin appears generationally consistent with a dominant trait, supporting the presence of an overactive (gain-of-function) Biol202 allele. Thus, Hypothesis #2 is most plausible.

Question 2 (a): Unattached earlobes (EE or Ee) are dominant over attached earlobes (ee). A couple both displaying unattached earlobes have parents with attached earlobes.
- Genotype of the Couple:
- Male: Ee
- Female: Ee (both parents appear ee, thus they must be heterozygous.).
Question 2 (b): The couple has four children, all with attached earlobes.
- Concern: Possibility of infidelity?

Calculation:
- Probability of one child having attached earlobes (ee): $rac{1}{4}$
- Probability of four children all having attached earlobes: $\bigg( rac{1}{4}\bigg)^{4} = rac{1}{256}$
- Conclusion: There is a 1 in 256 chance of all four children having attached earlobes purely by chance.

Understanding Rare Traits:
- Assume that mates do not carry the rare trait they do not exhibit.
Probability Principles:
- OR Rule: Add the probabilities.
- AND Rule: Multiply the probabilities.
General Observations for Trait Inheritance:
- A disorder appearing in every generation is typically dominant; if it skips generations, it may be recessive.
- If affected fathers don't pass traits onto sons, it indicates a likely X-linked trait, which is often more pronounced in males.