03/26 BIO101 lab

Introduction to the Lab

• The lab is a computer-based session.
  • Students can use their personal computers or provided laptops.
  • Phones may also be used for the session.

Overview of Genetic Inheritance

• Focus topic: Mendelian genetics and heredity.
• Students will view an Amoeba Sisters video as part of the lecture.

PTC and Genetic Sensitivity

• PTC (Phenylthiocarbamide): A chemical used in genetics studies to illustrate taste sensitivity.
  • Sold on strips known as PTC paper.
  • Some individuals can taste PTC (described as bitter), while others cannot.
  • Personal anecdote: The speaker reveals their inability to taste PTC, contrasting with their peers who can.

Genetic Basis of PTC Sensitivity

• The ability to taste PTC is genetically determined.

  • Genes are segments of DNA that encode characteristics.
  • Example trait: PTC sensitivity.

• Genetic complexity of traits: Many traits result from interactions among multiple genes.

  • Eye color as an example of a complex trait influenced by several genes.
  • Variability (e.g., different alleles influencing taste perception).

Genetic Inheritance and Chromosomes

• Humans have 46 chromosomes arranged in 23 pairs.
  • 23 chromosomes inherited from the mother and 23 from the father.
  • Each chromosome contains genes including the PTC sensitivity gene.

Alleles and Genotypes

• Allele: A variant form of a gene.
  • Example notations: ( T ) (dominant) and ( t ) (recessive).
  • Genotype combinations include ( TT ), ( Tt ), and ( tt ).
• Genotype determines phenotype (physical characteristics).

Dominant vs. Recessive Traits

• Dominant trait (Taster): Required presence of at least one dominant allele.
• Recessive trait (Non-taster): Expressed only when two recessive alleles are present:
  • Phenotypes for tasting PTC:
  • Genotypes
    • ( TT ): Tastable.
    • ( Tt ): Tastable.
    • ( tt ): Non-tastable.

Parental Genotypes in Example

• The speaker's parents (both tasters) must have the genotype ( Tt ).
  • Thus, the speaker inherited ( tt ) causing their non-taster phenotype.

Punnett Squares

• Punnett squares: A tool for predicting the probability of offspring genotypes and phenotypes.
• Not discussed in-depth here as it’s covered in a separate Amoeba Sisters video.

Misconceptions on Dominance

• Dominance does not necessarily equate to commonality in a population.
  • Example: Some dominant traits can be rare (e.g., certain forms of polydactyly).

Genetic Traits and Examples

• Discussion on other observable traits:
  • Hair color, eye color.
  • Traits that are observable and can be inherited.
• Importance of physical characteristics:
  • Recognized as phenotypes relating to genetics.

Chromosomes and Genes

• Reinforcement of the fact humans have 46 chromosomes made of DNA.
  • Genes are specific DNA segments that code for traits (e.g., hair color).

Examples of Traits and Alleles

• Hair color alleles example:
  • ( G ) (Ginger - dominant) and ( g ) (non-ginger - recessive).
• Eye color example:
  • ( B ) (Brown - dominant) and ( b ) (Blue - recessive).

Genetic Terminology

• Genotype: The genetic constitution (e.g., ( GG ), ( Gg ) for hair color).
• Phenotype: The observable physical characteristic (e.g., ginger hair).

Types of Genotypes

• Homozygous: Two identical alleles (e.g., ( GG ) or ( gg )).
• Heterozygous: Two different alleles (e.g., ( Gg )).
• Identification of genotypic types based on allele combinations.

Punnett Square Practice

• Working with Punnett squares to estimate probabilities.
  • Example trait: Straight thumb (dominant ( T )) vs. Hitchhiker's thumb (recessive ( t )).
  • Parent genotypes are used to predict offspring outcomes.

Ending Practice and Lab Transition

• Transition to practical lab session:
  • Investigations on genetic probabilities using computers.
  • Guidance provided through a link to supplemental resources.