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Today:

Presentations! Topic

Due Thursday!

Looking at Cell Division- Mitosis! (In-

Class 4)

Preview of Meiosis?

Why do cells do Mitosis?

1. Growth &

Development

2. Repair

What’s important about Mitosis?

Mitosis (cell division) must be very precise for

both DNA replication (more later) and parceling out the

DNA to the new cells!

Abnormal division triggers cancer…

Bladder cancer cells.

(Photo by Nancy Kedersha)

Words to Know: GENOME: the collection of all a cell’s genetic information

CHROMOSOMES: The packaging unit for DNA.

Each species has a characteristic number of chromosomes. (Humans = 46, except in sex cells) Chromosomes are composed of

CHROMATIN.

SISTER CHROMATIDS: As a chromosome is

duplicated, it forms a set of two sister chromatids. The chromatids have a narrow “waist” called the CENTROMERE.

A single

CHROMOSOME

duplicates to form a pair of

SISTER

CHROMATIDS, with a visible

CENTROMERE.

Homologous Chromosomes

DIPLOID organisms (like

us) have two of each chromosome

(one from each

parent). These pairs are called

HOMOLOGOUS Chromosomes.

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The Mitotic Cell Cycle: An Overview

~90% of the cell cycle

Mitosis Occurs in 4 Steps:

Prophase Metaphase Anaphase Telophase

Step 1: Prophase

Chromatin (DNA) condenses to form

‘visible’ chromosomes

Microtubules are reassembled, spindle begins to form

Nuclear envelope breaks up

Step 2: Metaphase

Spindle is complete

“Push-pull” aligns chromosomes at

the midpoint to form the

METAPHASE PLATE

Step 3: Anaphase

Sister Chromatids separate and

migrate towards opposite spindle

poles

Step 4: Telophase

Chromosomes arrive at poles and

relax

Nuclear membrane reforms

Spindle is disassembled

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CYTOKINESIS Let’s Watch!

Check out these cancer cells: http://www.microscopyu.com/moviegallery/livecellimaging/a549/index.html

Or Mitosis in a Pig Kidney Cell:

http://www.microscopyu.com/moviegallery/c1si/mitosiseb3/index.html

Last but not least, Lung of Newt! http://video.google.com/videoplay?docid=-990474875075679903&ei=7cDgSsKCNZWUqAPP-

f3CDA&q=mitosis+in+newt+lung&hl=en#

Modeling Mitosis

With a neighbor or two, build some chromosomes! If you are building sister chromatids, make them the same color and length.

If building homologous chromosomes, make them

different colors but the same length. With your group, walk

through each stage, making sure you can explain what’s

happening at each!

Fill-in Part 1, AC

Asexual vs Sexual Reproduction

Advantages and Disadvantages?

Asexual

Reproduction occurs

through MITOSIS and

CYTOKINESIS

The resulting

offspring are

CLONES! (genetically

identical to the

parent)

Sexual Reproduction Genetic

Variation!

Through sexual reproduction, offspring inherit

new combinations of alleles.

An ALLELE is a “version” of a particular gene

Genetic Diversity is

Essential for Evolution!

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Sexual

Recombination

Requires

Haploid

Gametes

A Graphical

Overview of Meiosis

Meiosis occurs in two stages:

Meiosis I- Homologous chromosomes separate

Meiosis II- Sister

chromatids separate

Meiosis II Meiosis II

You Try: 2AC

Meiosis Creates Genetic

Diversity:

Crossover

Homologous

Chromosomes are

INDEPENDENTLY (randomly)

parceled out during

Meiosis I

Meiosis Creates Genetic Diversity: Random Fertilization

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8 million possible

chromosome

combinations in each egg, and each sperm…

= >70 trillion possibilities!

Meiosis Creates Genetic Diversity: Random Fertilization

Meiosis: What can go wrong??

You Try: 2D

Nondisjunction can result in an abnormal chromosome number

Red viscacha rat from Argentina = 4n

XXY = Klinefelter Syndrome-

male with normal

intelligence, sterile

XO = Turner syndrome-

phenotypically female, sterile, usually normal

intelligence

XYY = no general traits (tall)

XXX = healthy, “normal”

Nondisjunction can result in an abnormal chromosome number