General Biology Exam 4 Study Guide: Cell Cycle, Mendelian Genetics, and Molecular Basis of Inheritance

Exam 4 Study Guide Overview

This study guide covers key topics for a General Biology exam, focusing on the cell cycle, Mendelian genetics, and the molecular basis of inheritance. The guide is divided into online and in-class portions, with specific chapters and concepts highlighted for review.

The Cell Cycle

Phases and Regulation

The cell cycle is the series of events that cells go through as they grow and divide. It consists of interphase (G1, S, G2) and the mitotic phase (mitosis and cytokinesis).

• Interphase: Includes G1 (cell growth), S (DNA replication), and G2 (preparation for mitosis).

• Mitotic Phase: Consists of mitosis (nuclear division) and cytokinesis (cytoplasm division).

• Regulation: Controlled by cyclins and cyclin-dependent kinases (CDKs). These proteins ensure proper timing and order of cell cycle events.

Example: Cyclin-CDK complexes regulate transitions between cell cycle phases, such as the G1/S and G2/M checkpoints.

Cell Cycle Control and Cancer

• Checkpoints: Critical control points where stop and go-ahead signals regulate the cycle.

• Cancer: Results from uncontrolled cell division due to mutations in genes regulating the cell cycle.

Additional info: Cancer cells often bypass normal checkpoints, leading to tumor formation.

Mendel and the Gene Idea

Principles of Inheritance

Gregor Mendel's experiments with pea plants established the foundational principles of genetics.

• Law of Segregation: Each individual has two alleles for each gene, which segregate during gamete formation.

• Law of Independent Assortment: Genes for different traits assort independently during gamete formation.

• Dominant and Recessive Traits: Dominant alleles mask the expression of recessive alleles.

• Genotype vs. Phenotype: Genotype is the genetic makeup; phenotype is the observable trait.

• Test Cross: Used to determine the genotype of an individual expressing a dominant trait.

Example: Crossing a pea plant with yellow seeds (dominant) with one with green seeds (recessive) can reveal the genotype of the yellow-seeded plant.

Patterns of Inheritance

• Complete Dominance: One allele completely masks the other.

• Incomplete Dominance: Heterozygotes show an intermediate phenotype.

• Codominance: Both alleles are fully expressed (e.g., AB blood type).

• Multiple Alleles: More than two alleles exist for a gene (e.g., ABO blood group).

Additional info: Pedigree analysis is used to track inheritance patterns in families.

Molecular Basis of Inheritance

DNA Structure and Replication

DNA is the hereditary material in all living organisms. Its structure and replication are central to genetics.

• Double Helix: DNA consists of two antiparallel strands forming a double helix.

• Nucleotide Composition: Each nucleotide contains a phosphate group, deoxyribose sugar, and a nitrogenous base (A, T, C, G).

• Base Pairing: Adenine pairs with thymine; cytosine pairs with guanine.

• Replication: DNA replication is semi-conservative, producing two identical daughter molecules.

Key Equation:

$\text{DNA Replication:} \, \text{Parent DNA} \rightarrow \text{Two Daughter DNA Molecules}$

Discovery of DNA Structure

• Watson & Crick: Proposed the double helix model based on X-ray diffraction data from Rosalind Franklin.

• Chargaff's Rules: Amount of A = T and C = G in DNA.

Example: The Hershey-Chase experiment confirmed DNA as the genetic material.

DNA Replication Enzymes

• Helicase: Unwinds the DNA double helix.

• DNA Polymerase: Synthesizes new DNA strands by adding nucleotides.

• Ligase: Joins Okazaki fragments on the lagging strand.

Blood Typing and Genetics

ABO and Rh Blood Groups

Blood types are determined by the presence or absence of specific antigens on the surface of red blood cells.

• ABO System: Three alleles (IA, IB, i) determine four blood types: A, B, AB, O.

• Rh Factor: Presence (+) or absence (–) of Rh antigen.

• Inheritance: Blood type inheritance follows Mendelian patterns, with codominance in the ABO system.

Example: A parent with genotype IAIB (AB blood type) and a parent with genotype ii (O blood type) can have children with blood types A or B.

Blood Typing Table

Genotype	Phenotype (Blood Type)
IAIA or IAi	A
IBIB or IBi	B
IAIB	AB
ii	O

Additional info: Rh factor is inherited independently of the ABO system.

Topics Not Required for Study

Excluded Content

Certain topics from chapters 12, 14, and 16 are not required for this exam, including binary fission in bacteria, Mendel's life, probability laws, and DNA repair mechanisms.

• Binary fission in bacteria

• Specific details of Mendel's life and pea plant traits

• Probability laws (multiplication/addition) in genetics

• DNA proofreading and repair

• Replication of the ends of DNA molecules

Additional info: Focus your study on the cell cycle, Mendelian genetics, and DNA structure/replication for this exam.