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- Double-stranded molecule made of

nucleotides that stores genetic information

(double helix)

How does it store it?

- as a long, continuous thread that consists

of many genes

Chromatin: loosely compacted single strand

Chromatid: tightly compacted, one of a pair

Chromosome: two tightly compacted sister

chromatids joined at the centromere

Humans have 23 pairs of chromosomes:

Autosomes

- chromosome pairs 1 through 22

- contain genes not directly related to the sex

of an organism

Ex. Eye and hair color

Sex Chromosome

- the 23rd pair of chromosomes

- control development of sex characteristics

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Gametes: sex cells

- female (egg)

- male (sperm)

*** DNA in gametes is

passed on to

offspring

Somatic Cells: body

cells

- make up tissue

and organs

*** DNA is NOT

passed on to

offspring through cell

division

Why do cells need to divide?

1- growth

2- reproduction3- repair

1. Interphase

- where DNA duplicate and form

chromosomes

2. Mitosis

- where the chromosomes divide and

separate from each other

3. Cytokinesis

- Cytoplasm divides into two daughter cells

90% of the cell cycle is spent in interphase

Chromosomes appear as loose coils called

chromatin

Three phases:

Gap 1, Synthesis and Gap 2

The cell grows and checks DNA to make

sure code is undamaged then it duplicates

the DNA and checks it again for any

damaged code

Occurs in 4 phases:

PMAT

First stage of Mitosis

- DNA long strands condense into short coils

- Nuclear envelope breaks down

- Centrioles begin to move to opposite poles

- Spindle fibers form

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Chromosomes line up in the center of the cell

Spindle fibers attach to the centromere of each chromosome

Spindle fibers shorten and pull sister

chromatids apart, towards opposite poles

2 nuclear membranes begin to form around

chromosomes (one for each new cell)

Chromosomes begin to uncoil

Spindle fibers fall apart

Divides cytoplasm into two cells and

completes a full stage of the cell cycle

Begins during Telophase

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Meiosis consists of two cell divisions without

Interphase in the middle

Occurs in gametes (sex cells) only

Mitosis is in my toes; Meiosis is in the ovaries

OR

Meiosis is what makes me unique (genetically

unique as opposed to a genetic duplicate)

When your skin cells replicate, you want them

to create an exact copy (mitosis)

When creating a new organism

(reproduction), genetic variation increases

survival of the species (meiosis).

Egg and sperm each have 1 set of DNA

- Sex cells are called haploid cells

(n = 23 chromosomes)

When the sperm fertilizes the egg, the

resulting zygote now has 2 sets of DNA

- Somatic cells are called diploid cells

(2n = 46 chromosomes)

Fertilization:

- egg and sperm come together and the cell

now has a complete set of DNA (23 pairs, one

from each parent)

Cell makes a copy of DNA from Mom and from Dad.

23 from egg duplicates to 46

23 from sperm duplicates to 46

Total chromosomes is 92

- Copies of each chromatid are made; they join at the

centromere (cell must reduce chromosome number)

- Homologous chromosomes pair up: one from each

parent

- Crossing over may occur

Nuclear membrane disappears

Centrioles move to poles

Spindle fibers form

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Chromosome pairs line up at equator of cell

Spindle fibers attach to one of each

chromosome pair

Chromosomes line up

randomly on either side of

the equator

Paired chromosomes are pulled apart by

spindle fibers

Each side will have some from Mom and

some from Dad

Nuclear membranes form around two sets of

DNA; spindle fibers detach

Cytokinesis forms two unique cells, each with

23 pairs of chromosomes

Second cell division

Prophase II

Metaphase II

Anaphase II

Telophase II

Cytokinesis that

results in 4 genetically

unique daughter cells

egg + sperm = zygote

haploid + haploid = diploid

n + n = 2n

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Mitosis MeiosisDiploid or Haploid daughter cells

# of Divisions

Cell Type

Number of daughter cells

Daughter cells are:

Diploid (2n=46) Haploid (n=23)

1 2

2 4

Somatic cells(body cells)

Sex Cells(gametes)

Genetically identical Genetically unique

Interphase Gap 1 (G1)

Synthesis (S)

Gap 2 (G2)

Mitosis Prophase

Metaphase

Anaphase

Telophase

Cytokinesis

INTERPHASE HAS THREE PHASES

Interphase Gap 1 (G1)

Synthesis (S)

Gap 2 (G2)

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Interphase Gap 1 (G1)

During G1 the cell grows, caries out normal functions, and replicates its organelles. There is also a CRTICAL CHECKPOINT. The cell checks to see if it has enough nutrition, has adequate size, and that DNA is undamaged.

Interphase Gap 1 (G1)

Synthesis (S)

During Synthesis (S phase) DNA is synthesized (made) that is: copied, replicated, duplicated.

Interphase Gap 1 (G1)

Synthesis (S)

Gap 2 (G2)

During G2 the cell undergoes additional growth. There is also a CRITICAL CHECKPOINT.

The cell checks to see if it has enough nutrition, has adequate size, and that DNA is undamaged.

Interphase

Mitosis Prophase

Metaphase

Anaphase

Telophase

CytokinesisCytoplasm divides,

the cell divides.