Biology
The Cellular Basis of Inheritance
Why Do Cells Divide?
Cell ______________________________________ is the splitting of a single cell into 2 cells. 3 life processes occur:

Growth : this is the _______________________________________________________ of in size .

______________________________________________ is the specialization in cells .

Repair : this is the ability of an organism to ________________________ itself ; humans repair their skin blood vessels and bone.

Regeneration is the ability of an organism to ________________________________ a missing body part (like a starfish regrowing an arm).

_____________________________________________ : When an organism is single-celled and that cell divides, it is reproducing . This is a form of
_____________________________________________ reproduction . o Bacteria and unicellular eukaryotes reproduce this way.

The arm that broke off from the starfish can also reproduce asexually by cell division. It slowly regrows a new body.

Asexual reproduction produces genetically _________________________________________ offspring to the parents .
Sexual Reproduction:

Sexual reproduction produces genetic __________________________________ in offspring.
o Plants and animals reproduce this way. This results in a recombination of chromosomes through _____________________________________, a
How Do Cells Divide?

The cell _____________________________________ is the sequence of phases in the life cycle of the cell

The cell cycle has 2 parts: ___________________________________ ( Growth and preparation ) and Cell Division

Cell Division includes: _______________________________________ (nuclear division) and
_______________________________________ (cytoplasm division) .
Some Terms:


_________________________________________ is the fibrous form of DNA and proteins that make up chromosomes . o This is what is found within the nucleus of the cell during
_______________________________________________ . o It is ___________________________________________ DNA .

Once chromosomes have been replicated, they are paired together in the form of
___________________________________________ chromatids . o These are identical structures that are side by side .

Sister chromatids are held together by a
_________________________________________________ . o This is the point of attachment .
Cell Division:
Interphase:

G1, or ______________________________________________ , is characterized by growth and development.

S stage, or ____________________________________________ , is when the chromosomes are _____________________________________________.

G2, or ______________________________________________ , is when the cell synthesizes organelles and other materials.

This is the ____________________________________________ phase of the entire cell cycle . The cell is in preparation for the nucleus to divide.
Mitosis is the formation of 2 nuclei from 1. It occurs in 4 stages (PMAT)
1. Prophase:

Chromosomes _______________________________________ & become
__________________________________________ under the lightmicroscope

Microtubules from the mitotic spindles

The nuclear envelope & nucleolus break apart &
_________________________________________________

Centromeres attach to the spindle fibers
2. Metaphase:

The chromosomes move to the ______________________________________ of the cell

The center of the cell is called the metaphase ______________________________
3. Anaphase:


Centromeres divide & the spindle fibers pull 1 set of sister chromatids toward
___________________________________________________________________

Once chromosomes are at opposite poles, anaphase is over
4. Telophase:

A ______________________________________________________________ forms around each set of chromosomes

Chromosomes uncoil into __________________________________________

Mitotic spindle fibers disassemble
Cytokinesis:

This is a.k.a.
____________________________________________separation

In animal cells, this begins in telophase as the nuclei reform . o This starts at the center of the cell and pinches
_______________________________________________.
This is called a
_______________________________________________________________ .

In plant cells, this begins in anaphase and starts in the center of the cell along the metaphase plate and grows ___________________________________. o This is called the
________________________________________________________________ .
Cancer

Tumors : __________________________________/clusters of cells o _________________________________________ : non-cancerous o Malignant : ______________________________________ ( usually uncontrolled dividing cells )

_________________________________________________ : spreading of cancerous cells

Treatment: surgery ( removes tumor ), radiation &
__________________________________________________ ( destroys cells by disrupting cell cycle )

Radiation & chemo side effects: healthy cells may die, sterility, hair loss, nausea
What is Meiosis?
Remember that humans have 46 chromosomes (or 23 pairs) in their cells.

This means they have 2 complete __________________________ of chromosomes.

________________________________________, or 2n , is a cell that has 2 complete sets of chromosomes (in humans, 46).


Haploid, or ___________________ or n , is a cell that has only 1 set of chromosomes (in humans, 23) .

Human
’ s sex cells , or _________________________________________, are haploid .

All human body cells are produced through
__________________________________________ whereas the sex cells, or gametes, are produced through _________________________________________.

Gametes are _____________________________________ and
___________________________________ and have only 23 chromosomes in each. o When they fuse (at fertilization), they form a
______________________________________________ (23 + 23= 46). o This is how each generation remains stable.

Meiosis is a type of cellular reproduction in which the # of chromosomes are reduced by
½ so that the daughter cells are ______________________________________________ (n).

______________________________________________ pairs are pairs of chromosomes. o Each of the 23 chromosomes has a matching chromosome (with 1 exception: the
_________________________________ chromosomes).
o Sex chromosomes are ___________________ and _____________________.
The Phases of Meiosis:

Prior to meiosis, a diploid cell replicates its chromosomes (Interphase).

Meiosis has 2 stages: Meiosis I and Meiosis II.
Each has 4 phases .
Meiosis I:
1.
Prophase I: chromosomes condense, homologous chromosomes become attached to each other, each homologous chromosome contains 4 sister chromatid (this is called a
________________________________________ , meaning 4 ).
2.
Metaphase I: _________________________________________ pairs align along the middle of the cell.
3.
Anaphase I: homologous pairs _____________________________________________.
4.
Telophase I and Cytokinesis: Nuclei reform and the cells split. This result is 2
_____________________________________________ cells, each with 2 complete sets of chromosomes.
Meiosis II:
1.
Prophase II: Spindle fibers form again & chromosomes condense . _____________ tetrads; ____________ crossing over!

2.
___________________________________: chromatids move to the center of the cell.
3.
Anaphase II: chromatids are pulled to opposite _____________________________.
4.
Telophase II and Cytokinesis: Nuclei reform and cells separate. The result is
________________________________________________ cells .

In human males, 4 haploid cells result (sperm cells) but in human females, only 1 of the 4 haploid cells forms an egg cell. The other 3 receive no cytoplasm and do not form gametes
(they disintegrate).

Interphase occurs only _____________________________________________(Meiosis I), meaning chromosomes replicate only 1X.
What are the differences between mitosis and meiosis?

Meiosis produces daughter cells with
½
the # of chromosomes
(_____________________________________ cells), mitosis produces
______________________________________ cells.

Meiosis produces daughter cells that are NOT genetically identical to each other (the homologous chromosomes separation is
_________________________________________); mitosis produces
_________________________________________ copies of parent cells.

Meiosis produces ______________________ haploid cells; mitosis produces 1 cell.
Genetic Variation
 Variation results from the _________________________________________ of DNA (from meiosis & fertilization) and accounts for the differences between members of a population.
Sources of Genetic Variation:

Random ____________________________________________ of homologous pairs of chromosomes

Random combination of haploid
_____________________________________________________

___________________________________________________ Over (tips of homologous chromosomes switch places) occurs during prophase I (meiosis I)