BICD Lecture 6 Week 2

Review Access
- Students will have access to review study materials but may take the practice test only once.
Time Commitment
- Students may need more than one session to complete the materials.
- Guidance to manage time effectively (e.g., start early and revisit if necessary).
Post Midterm
- Explanation of the grading process and how to demonstrate completion to TAs.
- Students must show their solutions to TAs to receive points.
Support Sections
- Availability of additional sections for asking questions and obtaining help.

Traits Under Discussion
- Eye color and wing structure in butterflies, with specific focus on two genes:
  - Eye Color: Red (dominant allele, denoted as Big R) and recessive allele (little r).
  - Wing Structure: Plain (dominant allele, denoted as Big T) and recessive allele (little t).
F1 and F2 Generation Calculation
- F1 genotype established as Big R (homozygous dominant).
- Gametes and the F2 progeny distributions illustrated.
- Punnett square utilized for gamete combination analysis:
  - Gamete combinations: Big R Big T, Big R little T, little r Big T, little r little t.
- Calculation of offspring phenotypes and probabilities:
  - Example: What is the probability of a phenotype having dominant W trait and recessive Y trait.

Independent Assortment
- Application of Mendel's laws of independent assortment for problem solving.
- Breakdown genetics problems into manageable components (e.g., W and Y traits treated separately).
Calculating Probabilities
- Probabilities combine for independent events:
- Dominant W trait probability:
  - Cross results in a probability of $rac{3}{4}$ for Big W.
- Recessive Y trait probability:
  - Cross results in a probability of $rac{1}{4}$ for little y.
- Final calculation for both events being true:
- Combined probability equals $rac{3}{4} imes rac{1}{4} = rac{3}{16}$ for being dominant W phenotype and recessive Y phenotype.

Traits and Crosses
- Mendel's summary of seven traits in pea plants.
- Focus on wild type strains versus variant traits, highlighting the differences and significance in genetics experimentation.
One Factor vs. Two Factor Crosses
- Explanation: Crosses can be simplified into one factor or two factor crosses based on how traits segregate. Important to understand the unique aspects of each method:
  - One Factor Cross: A single trait examined at a time (e.g., Yellow vs. Green).
  - Two Factor Cross: Two traits are considered together (increased complexity but more insightful).
Data Analysis and Genetic Mapping
- Streamlined data collection by cross-reference of alleles.
  - Using gene attributes (e.g., A, B, C) to assess how traits vary when segregated.
- Utilization of observed ratios for interpretations.

Utility of Test Crosses
- Test crosses as a method to reveal the genotype of mystery organisms by crossing them with known homozygous recessive individuals.
- Generation of offspring phenotypes directly yields information about baselines and parental contributions.
Example Calculation of Expected Traits
- Scenarios analyzing dominant versus recessive traits and the associated probabilities.
True Breeding
- Definition of true breeding individuals (either homozygous dominant or recessive) and implications for phenotypes of offspring.

Polygenic Inheritance and Continuous Traits
- Unlike Mendelian traits, continuous traits (like height or skin color) are influenced by multiple genes (polygenic).
- Allelic Series: A single gene may have many alleles (a1,a2,a3…a1,a2,a3…) which variations in protein function or quantity.
Phenotypic Variation: Traits often follow a normal distribution (bell curve) in a population due to the additive effects of multiple alleles and environmental influences.
Genetic Mapping and Logic: By observing how often traits are inherited together, scientists can determine the physical proximity of genes on a chromosome, though Mendelian rules assume no linkage for simplicity.