Notes, summaries, assignments, exams, and problems for Biology

Mendel's Pea Plants: Ideal Study Subjects

Mendel chose pea plants for genetic studies due to several key advantages:

1. They produce a large number of offspring, allowing for more data collection.
2. The plants can be easily grown in a small space.
3. They have a simple genetic structure, making it easier to study inheritance patterns.

Understanding the Test Cross

A test cross is used to determine the genotype of an individual exhibiting a dominant phenotype by crossing it with a homozygous recessive individual. This method reveals the genetic makeup of the dominant organism.

Test Cross Outcomes (Example)

• If all offspring are red, the red plant is probably homozygous (RR).
• If you get both red and white offspring, the red plant is heterozygous (Rr).

Genetic Probability

Species Concepts

• Biological Species Concept (BSC)

  Species are groups of interbreeding natural populations that are reproductively isolated from other groups. This means no viable, fertile offspring with members of other species.

• Phylogenetic Species Concept

  A species is the smallest group that shares a common ancestor and can be distinguished by unique traits.

• Ecological Species Concept

  Defines a species by the ecological niche it occupies, including interactions with the environment and other species.

• General Lineage Concept

  Considers species as independently evolving metapopulations.

Isolating Barriers

• Geographic (Extrinsic) Barriers

  Landscape features physically prevent gene flow (e.g., mountain ranges, oceans).

• Reproductive (Intrinsic) Barriers

  Biological

Benign Epithelial Lesions

Squamous Cell Papilloma

Age: Mid-age
Site: Palate, uvula, cheek, lip, tongue, gingiva
Characteristics:

• Color: White to pinkish (depending on keratinization)
• Shape: Cauliflower-like
• Surface: Rough, irregular (finger-like projections)
• Texture: Firm or soft (depending on keratinization)
• Sessile or pedunculated

Histological Features:

1. Hyperplastic stratified squamous epithelium
2. Acanthosis and hyperkeratosis
3. Intact basal layer
4. Thin central branching core of connective tissue carrying nutrition

Verruca Vulgaris (Wart)

Reactive lesion, autoinoculation
Etiology: HPV 2, 4, 6
Histological Features:

1. Intranuclear inclusion bodies
2. Koilocytes
3. Cupping effect of rete ridges
4. Granular cell layer

Keratoacanthoma

True, self-limiting lesion
Age: Older males
... Continue reading "Benign Epithelial and Mesodermal Lesions of the Oral Cavity" »

Core Ecology Concepts

Biodiversity

• Definition: Variety of all living things in one area.
• Importance: Increases stability and health of ecosystems.
• Threats: Pollution, deforestation, climate change, invasive species.

Ecosystems

• Definition: A system of living (biotic) and nonliving (abiotic) things interacting.
• Biotic Components: Plants, animals, fungi.
• Abiotic Components: Water, sunlight, soil, air, temperature.
• Producers' Role: Make food from sunlight (photosynthesis).
• Balance: All parts depend on each other.

Energy Pyramid

• Purpose: Shows how energy moves through trophic levels.
• Trophic Levels: Producer → Primary → Secondary → Tertiary.
• Energy Transfer: Only 10% passed to the next level; 90% is lost as heat.
• Fewer Top Predators: Less energy is available

Mendel's Laws of Inheritance and Genetic Crosses

Mendel's Laws of Inheritance

1. Law of Segregation: Each parent contributes only one of their two alleles for a specific trait to their offspring.
2. Law of Independent Assortment: Alleles for different traits are passed down independently of one another during gamete formation.
3. Law of Dominance: When an organism inherits two different alleles for a trait, the dominant allele will be expressed in the phenotype, masking the effect of the recessive allele.

Analyzing Monohybrid Inheritance

Case Study: Earlobes (Monohybrid Cross)

The results of the cross show:

• Mr. Jones: aa (Attached earlobes, recessive)
• Mrs. Jones: Aa (Free earlobes, heterozygous dominant)

Their children exhibit the following genotypes and phenotypes:... Continue reading "Genetic Inheritance: Mendel's Laws, Crosses, Ratios, and Probability" »

Differential Diagnosis of Oral Ulcers and Vesiculobullous Lesions

Classification by Number and Etiology

• Single Ulcers: Traumatic, Tuberculosis (TB), Primary Syphilis.
• Multiple Ulcers: Recurrent Aphthous Stomatitis, Herpetic Stomatitis, Erythema Multiforme, Pemphigus Vulgaris.

Classification by Location

• Keratinized Mucosa: Recurrent Intraoral Herpes, Mucous Membrane Pemphigoid, Major Aphthous Ulcers.
• Non-Keratinized Mucosa: Minor Aphthous Ulcers, Herpetiform Ulcers.

Classification by Clinical Features

• Ulcers Causing Scarring: Major Aphthous Ulcers, Mucous Membrane Pemphigoid Ulcers, Tertiary Syphilis.
• Painless Ulcers: Tuberculosis (TB), Primary Syphilis, Tertiary Syphilis.
• Painful Ulcers: Primary Herpetic Gingivostomatitis, Recurrent Intraoral Herpes,

Anatomy and Physiology Fundamentals

Anatomical Terminology

• Anatomical Descriptors
  • Anterior — at or near the front of the body
  • Posterior — at or near the back of the body
  • Midline — imaginary vertical line dividing the body equally
  • Lateral — farther from the midline
  • Medial — nearer to the midline
  • Superior — toward the head or upper part of a structure
  • Inferior — away from the head or lower part of a structure
  • Superficial — close to the surface of the body
  • Deep — away from the surface of the body
  • Proximal — near the origination of a structure
  • Distal — farther from the origination of a structure
  • Contralateral — on the opposite side
• Anatomical Planes
  • Sagittal — body divided into left and right halves by a vertical plane passing through

Circulatory System

Deoxygenated blood from the body returns to the right atrium of the heart through the superior and inferior vena cavae. The right atrium contracts, pushing the blood through the tricuspid valve into the right ventricle. The right ventricle contracts, pumping the deoxygenated blood through the pulmonary valve into the pulmonary artery. The pulmonary artery carries the deoxygenated blood to the lungs, where it picks up oxygen and releases carbon dioxide through the process of gas exchange. Oxygenated blood returns from the lungs to the left atrium of the heart via the pulmonary veins. The left atrium contracts, pushing the oxygenated blood through the mitral valve into the left ventricle. The left ventricle contracts, pumping... Continue reading "Understanding the Circulatory and Reproductive Systems" »

DNA Replication: Definition and Mechanism

Definition: DNA replication is the process of producing two identical copies of DNA from one original DNA molecule. It is bidirectional and semiconservative—each daughter DNA contains one parental (old) strand and one new strand.

Steps of DNA Replication

1. Unwinding of DNA: Hydrogen bonds between base pairs break.
   • Two antiparallel strands separate, starting at the origin of replication.
   • The enzyme Helicase unwinds DNA, forming a replication fork.
2. Nucleotide Activation: Deoxyribonucleotides are activated using energy and the enzyme phosphorylase.
3. Strand Cutting and Stabilization: Endonuclease cuts the DNA at A-T rich regions (fewer hydrogen bonds).
   • Topoisomerase and helix destabilizing proteins stabilize the