Equal and Unequal Cytokinesis

Cytokinesis

process of dividing the cytoplasm of a parent cell into two daughter cells

When does cytokinesis occur?

After nuclear division

physically seperating the cell into 2 distinct cells

What else is distributed between the daughter cells? 

Cytoplasm 

Organelles 

Other cellular components 

What is equal cytokinesis? 

A balanced split

When does equal cytokinesis occur

most cases,

What does this ensure?

both cells receive the resources they need to survive and function?

Key features of Equal Cytokinesis

Symmetrical Division

Organelle Distribution

Purpose

Key features of Equal Cytokinesis: Symmetrical Division 

cytoplasm is divided evenly 

producing two daughter cells of similar size 

Key features of Equal Cytokinesis: Organelle Distribution

Each daughter cells recieves at least one mitochondrion and other essential organelles

purpose of equal cytokinesis

common in cells that need to grow, repair tissue, and maintain genetic uniformity

such as skin cells or root tip cells in plants

Unequal Cytokinesis

Assymetrical Divison

When does unequal cytokinesis occur?

In some cases

Why does unequal cytokinesis occur? 

Cell may be specialised to retain most resources 

Smaller cell may have a different function or may degenerate 

When does unequal cytokinesis occur?

when one daughter cell needs to be particularly large or well - resourced

Why must all daughter cells receive certain organelles 

As these organelles cannot be synthesized from scratch 

What organelles must be inherited?

Mitochondria

Chloroplasts

Endoplasmic Reticulum

Golgi Apparatus

Why must a mitochondria be inherited?

cannot be made from scratch

must be inherited from the parent cell

each daughter cell must receive at least one mitochondrion to produce ATP

Why must a chloroplast be inherited? 

can only arise from pre-existing chloroplasts 

must be passed down during division 

What organelles can form from pre-existing structures?

Endoplasmic Reticulum

Golgi Apparatus

What type of organelles must be distributed to daughter cells even if cytokinesis is unequal.

Organelles that can only be made by dividing pre-existing structures

Examples of unequal cytokinesis 

Budding Yeast 

Oogenesis in Humans 

Budding is a form of __________ reproduction in yeast where cytokinesis is highly _____.

asexual

unequal

Where does the small bud grows? 

forms on the surface of the parent yeast cell 

What happens to the nucleus?

Nucleus divides and one nucleus moves into the bud

What does the bud receive?

a small portion of cytoplasm and organelles

including at least one mitochondrion

What happens to the bud eventually? 

eventually detaches from parent cell 

becomes an independent daughter cell 

a scar remains on the parent cell at the budding site

What does budding yeast result in? 

Parent cell: large, retains most of the cytoplasm and organelles 

Daughter cell - small, functionable and capable of growth 

What is the second example of unequal cytokinesis?

Oogenesis in Humans

What is oogenesis?

production of egg cells in females

involves two rounds of unequal cytokinesis during meiosis

Stages of Oogenesis 

Formation of primary oocytes 

Meiosis 1 and First unequal cytokinesis 

Meiosis II and second unequal cytokinesis 

What happens in Stage 1: formation of primary oocyte?

Oogenesis begins in female fetus

Diploid Germ cells undergo mitosis and then enter meiosis I

become primary oocytes which are arrested in prophase I until puberty.

Stage 2 Meiosis I and First Unequal Cytokinesis: 

1. After __________, during each menstrual cycle, one primary oocyte completes __________.

2. Unequal __________ produces two distinct cells.

3. The __________ is a large cell that retains most of the __________, __________, and nutrients.

4. The __________ is a small cell with minimal cytoplasm that eventually __________.

puberty

meiosis I

cytokinesis

secondary oocyte 

cytoplasm

organelles 

first polar body 

degenerates

Stage 3: When happens in fertilization occurs?

the secondary oocyte completes meiosis II

What does unequal cytokinesis produce?

Mature ovum egg

Second polar body

What does oogenesis in humans start in? 

One large functional egg — supports a developing embryo 

2 or 3 small polar bodies that degenerate