BIOL 235|Biology 235 Human Anatomy and Physiology
2026 Complete exam Study Guide Athabasca University
Complete Study Guide: Cell Cycles, Mendelian Genetics &
Chromosomal Inheritance
A plain-English breakdown of three big topics: (1) how cells grow
and divide, (2) how Mendel figured out the rules of heredity, and
(3) how genes/chromosomes explain real inheritance patterns —
including human genetic disorders.
PART 1: EXTENSIVE DEEP-DIVE REVIEW
SECTION A — THE CELL CYCLE (Chapter 8)
A.1 The Big Picture
,Every cell alive today came from a previous cell dividing. That's
true going back billions of years — an unbroken chain. Cells need
to divide for a bunch of reasons:
• Growing a population (bacteria multiplying)
• Growing tissue (a plant growing new leaves)
• Reproducing asexually
• Replacing worn-out cells (your gut lining, skin)
• Repairing wounds
The catch: division has to be precise. If a cell divides too fast,
daughter cells can end up too small or missing pieces of genetic
material. If it divides too slowly or incorrectly, cells can get too big
or accumulate extra chromosomes (which is often dangerous —
think cancer).
Three systems work together to make division safe and orderly:
1. Checkpoints — molecular "quality control" stations that
pause the cycle if something's wrong.
2. DNA replication — copying the genetic material precisely.
3. The cytoskeleton — the internal scaffolding/machinery
that physically pulls the copied DNA apart into two new cells.
Important note: Most cells in your body right now are not
dividing. They've matured into specific roles (a neuron, a muscle
cell, etc.) and mostly just do their job rather than reproduce.
A.2 Cell Division in Bacteria (Prokaryotes) — Binary Fission
,Bacteria (like E. coli) are simple: they have one circular
chromosome floating in a region called the nucleoid (they don't
have a nucleus — no membrane wrapping the DNA).
Their division process is called binary fission ("splitting into
two"). It happens in three conceptual periods:
• B period: The cell is born and grows before starting to copy
its DNA. (If food is abundant, bacteria can skip this step
entirely and start copying DNA almost immediately.)
• C period: DNA replication happens. Copying starts at a
specific spot called the origin of replication (ori), located
in the middle of the cell where the copying machinery sits.
As the origin gets copied, the two new copies of the origin
migrate to opposite ends (poles) of the cell while the rest of
the chromosome continues copying.
• D period: The cell membrane pinches inward in the middle
(like tightening a belt), a new cell wall forms, and the cell
splits into two daughter cells.
Under great conditions, E. coli can double its population every 20
minutes — that's how fast this process can run.
Old vs. new idea about how chromosomes separate: Scientists
used to think the chromosome copies passively rode along as new
membrane was added between them (like standing still on a
growing conveyor belt). Newer research shows this is actually an
, active process tied directly to the replication itself — not just cell
growth.
A.3 Why Eukaryotes Need Something Fancier: Mitosis
Bacteria can get away with a simple system because they only
have one chromosome — as long as a daughter cell gets a copy,
it has everything it needs.
Eukaryotes (like us) have their DNA split across multiple
chromosomes, each one much longer than a bacterial
chromosome. If a daughter cell misses even one chromosome,
that's usually lethal. Also, eukaryotic DNA lives inside a nuclear
membrane (the nucleus) for most of the cell cycle, unlike
bacterial DNA.
This called for a new mechanism: mitosis. The key innovation of
mitosis is that after DNA copies itself, the two identical copies
(called sister chromatids) stay physically attached to each
other. This lets the cell "keep track" of matching pairs and make
sure each daughter cell gets exactly one copy of each
chromosome.
Evolutionary side note: Different organisms show "in-between"
versions of this process — e.g., some single-celled algae keep
their nuclear envelope intact the whole time (chromosomes
attach to the inside of the membrane instead), while others
(yeast, diatoms) use a microtubule spindle without ever breaking
2026 Complete exam Study Guide Athabasca University
Complete Study Guide: Cell Cycles, Mendelian Genetics &
Chromosomal Inheritance
A plain-English breakdown of three big topics: (1) how cells grow
and divide, (2) how Mendel figured out the rules of heredity, and
(3) how genes/chromosomes explain real inheritance patterns —
including human genetic disorders.
PART 1: EXTENSIVE DEEP-DIVE REVIEW
SECTION A — THE CELL CYCLE (Chapter 8)
A.1 The Big Picture
,Every cell alive today came from a previous cell dividing. That's
true going back billions of years — an unbroken chain. Cells need
to divide for a bunch of reasons:
• Growing a population (bacteria multiplying)
• Growing tissue (a plant growing new leaves)
• Reproducing asexually
• Replacing worn-out cells (your gut lining, skin)
• Repairing wounds
The catch: division has to be precise. If a cell divides too fast,
daughter cells can end up too small or missing pieces of genetic
material. If it divides too slowly or incorrectly, cells can get too big
or accumulate extra chromosomes (which is often dangerous —
think cancer).
Three systems work together to make division safe and orderly:
1. Checkpoints — molecular "quality control" stations that
pause the cycle if something's wrong.
2. DNA replication — copying the genetic material precisely.
3. The cytoskeleton — the internal scaffolding/machinery
that physically pulls the copied DNA apart into two new cells.
Important note: Most cells in your body right now are not
dividing. They've matured into specific roles (a neuron, a muscle
cell, etc.) and mostly just do their job rather than reproduce.
A.2 Cell Division in Bacteria (Prokaryotes) — Binary Fission
,Bacteria (like E. coli) are simple: they have one circular
chromosome floating in a region called the nucleoid (they don't
have a nucleus — no membrane wrapping the DNA).
Their division process is called binary fission ("splitting into
two"). It happens in three conceptual periods:
• B period: The cell is born and grows before starting to copy
its DNA. (If food is abundant, bacteria can skip this step
entirely and start copying DNA almost immediately.)
• C period: DNA replication happens. Copying starts at a
specific spot called the origin of replication (ori), located
in the middle of the cell where the copying machinery sits.
As the origin gets copied, the two new copies of the origin
migrate to opposite ends (poles) of the cell while the rest of
the chromosome continues copying.
• D period: The cell membrane pinches inward in the middle
(like tightening a belt), a new cell wall forms, and the cell
splits into two daughter cells.
Under great conditions, E. coli can double its population every 20
minutes — that's how fast this process can run.
Old vs. new idea about how chromosomes separate: Scientists
used to think the chromosome copies passively rode along as new
membrane was added between them (like standing still on a
growing conveyor belt). Newer research shows this is actually an
, active process tied directly to the replication itself — not just cell
growth.
A.3 Why Eukaryotes Need Something Fancier: Mitosis
Bacteria can get away with a simple system because they only
have one chromosome — as long as a daughter cell gets a copy,
it has everything it needs.
Eukaryotes (like us) have their DNA split across multiple
chromosomes, each one much longer than a bacterial
chromosome. If a daughter cell misses even one chromosome,
that's usually lethal. Also, eukaryotic DNA lives inside a nuclear
membrane (the nucleus) for most of the cell cycle, unlike
bacterial DNA.
This called for a new mechanism: mitosis. The key innovation of
mitosis is that after DNA copies itself, the two identical copies
(called sister chromatids) stay physically attached to each
other. This lets the cell "keep track" of matching pairs and make
sure each daughter cell gets exactly one copy of each
chromosome.
Evolutionary side note: Different organisms show "in-between"
versions of this process — e.g., some single-celled algae keep
their nuclear envelope intact the whole time (chromosomes
attach to the inside of the membrane instead), while others
(yeast, diatoms) use a microtubule spindle without ever breaking
