Fundamentals of Genetics and Cell Biology Principles

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 Rules

Two fundamental laws govern genetic probability calculations:

• The Sum Law (Addition Rule): Calculates the probability of mutually exclusive events happening by adding their individual probabilities.
• The Product Law (Multiplication Rule): Calculates the probability of independent events happening together by multiplying their individual probabilities.

The Cell Cycle and Tumor Growth Control

The cell cycle is the essential process that cells undergo to grow and divide. It is divided into distinct stages:

1. G1 Phase: The cell grows and prepares for DNA synthesis.
2. S Phase: The cell synthesizes (makes a copy of) its DNA.
3. G2 Phase: The cell prepares for division.
4. M Phase (Mitosis): The cell actually splits into two new daughter cells.

To control tumor growth, researchers focus on the checkpoints and regulatory proteins within this cycle. By using treatments that help restore normal control mechanisms or encourage cancer cells to undergo apoptosis (programmed cell death), we can effectively slow down or stop tumor proliferation.

Meiosis: The Physical Basis of Inheritance

The behavior of chromosomes during meiosis provides the physical evidence supporting Mendel's laws of inheritance:

• Law of Segregation: Illustrated when homologous chromosomes separate during Meiosis I.
• Law of Independent Assortment: Demonstrated by the independent arrangement of non-homologous chromosomes at the metaphase plate.

In diploid organisms, this process ensures that every resulting gamete receives exactly one allele for every gene.

Comparing Cell Types: Eukaryotes and Prokaryotes

Eukaryotic Cells

Eukaryotic cells are complex cells characterized by:

• A defined, membrane-bound nucleus.
• Various membrane-bound organelles (e.g., mitochondria, endoplasmic reticulum).

They are found in organisms such as plants, animals, and fungi. An example is a human cell (though mature red blood cells are an exception as they lack a nucleus).

Prokaryotic Cells

Prokaryotic cells are simpler and significantly smaller. Key characteristics include:

• Lack of a true nucleus or membrane-bound organelles.
• Genetic material located in a region called the nucleoid.

Prokaryotic cells are mainly unicellular and include organisms like bacteria. An example is Streptococcus.