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Chromosome Structure

_______________________ - A "library" of genetic information. Consists of one long strand of __________ (_______%) wrapped around chunks of associated _________________ (________%). This occurs because all of the __________ needed in a cell cannot fit. Each chromosome contains thousands of _____________.

_______________________ - Joined strands off duplicated genetic material.

_______________________ - A protein disk that attaches chromatids to each other in a chromosome.


Chromosome Diagram



Chromosome Number

______________________ - A set of chromosomes present in a somatic cell (body cell). Ex: 46, XX = normal female; 46, XY = normal male

Somatic Cell (Body Cell)

Gamete (Sex Cell: sperm/ ovum)

46 chromosomes


Do not occur in pairs




Exist throughout the body


2 homologues of each chromosome

Only ONE of each chromosome


__________________ cells have _______ chromosomes, or ________ PAIRS of chromosomes Each pair of chromosomes #1 -> 23 in the cell is identical to one another, and contains the same _____________ in the same order.

___________________________ - Chromosomes # 1 -> 22 in the body. These are referred to as somatic cells, and they may be found ___________________________________________.

___________________________ - The 23rd set of chromosomes. These chromosomes determine the sex of an individual, male or female. They are designated as "_____" & "_____"

EXAMPLE: Female Karyotype = _________

Male Karyotype = _________

The sex of a child is determined by the ___________________ of that child. This is because females only have only type of sex chromosome to contribute to the child, _____ . Males, on the other hand, have both types of sex chromosomes to contribute, ______ & ______.


Genetic Diseases that Occur with an Abnormal Number of Chromosomes

Also referred to as "____________________________"

Karyotype - ____________

Phenotype (Physical characteristics caused by an abnormal genotype, or genetic make-up)

This is the most common genetic cause of mental retardation

Occurs in 1/800 live births

Higher incidence among mother over 35 years of age






Karyotype - __________


Occurs in 1/ 5,000 live births





Karyotype - ____________





Mitosis and Cell Division

Prokaryotic Cell Division (How BACTERIA reproduce)

_____________________________ - Process by which bacteria reproduce


Eukaryotic Cell Division

_____________________________ - Process by which a eukaryotic cell nucleus divides to form 2 nuclei, each containing a complete set of the cell’s chromosomes. In most cells, mitosis is followed by….

_____________________________ - Division of the original cell into 2 separate cells, each with its own nucleus.

________________ cells have cell walls that resist being ________________ _____________ like __________________ cell membranes. So they __________________________________ in the center of the cell. The new cell wall divides in half, resulting in _____________________.

After _____________________ & _________________________, each of the 2 new cells formed from the parent cell contains ______________ ________________ of all the ______________________ present in the ________________ cell.


The Cell Cycle

_____________________________ - Cycle of growth & division of a cell.


5 Phases of the Cell Cycle

_____________________________ - Most active phase of the cell cycle. Food is taken in, wastes eliminated, energy is converted, growth & differentiation occur. Cell makes copies of genetic material and duplicates organelles.

  1. __________________________ - "First gap" Intense growth occurs. This phase occupies most of the cell’s life.
  2. __________________________ - "Synthesis" The cell copies molecules of DNA in each of its chromosomes. These two molecules remain together, joined at the centromere
  3. __________________________ - "Second Gap" Cell continues to grow & prepares for cell division. Cell duplicates organelles.
  4. __________________________ - "Mitosis" Chromosomes arrange themselves along the "equator," or middle of the cell, and separate.
  5. __________________________ - "Cytokinesis" Cell divides in half and becomes two new, identical cells.




Phases of Mitosis 





Controlling the Cell Cycle

Researchers have discovered that animal cells use a class of proteins called _______________ to help control different phases of the ________________ _________________.

________________________ - Stimulates DNA replication in S phase

________________________ - Stimulates Mitosis

Cyclins are influenced by another class of proteins, called _____________________________. These proteins supervise & monitor a cell’s progress through the phases of the cell cycle.


They can:

This keeps the cell cycle in check, and prevents unnecessary __________________________.


Cancer Arises from a Faulty Cell Cycle

If the _______________________ _________________________ fails, cells can grow & divide without restraint. This result is a clump of cells called a ___________________.


Tumors may be:

________________________ - A disease characterized by uncontrolled cell division & growth

________________________ - A change in an amino acid sequence of a gene. It may be a random, spontaneous mistake or caused by exposure to environmental mutagens.

________________________ - A piece of a chromosome breaks off & reattaches itself to a non-homologous chromosome. Many cancers result in this, but this may also be random, resulting in Down Syndrome, or other forms of chromosomal abnormalities in individuals.



________________________ - A two-stage form of nuclear division in which the chromosome number is __________________. This is the manner in which ______________ are formed. Meiosis is often called ___________________ ____________________, because ______________ cells divide to become ________________ cells.

________________________ - A reproductive cell (egg or sperm). They are "_____________" ie, they contain _________ chromosomes in humans ("______").

Why do sperm & egg cells need to be haploid?




In sexual reproduction, _____ gametes fuse to form the 1st cell of a new individual.

In __________________________, or the _________________________________________, the number of chromosomes is cut in __________ by the separation of ____________________ ______________________.

In __________________________, or the _________________________________________, identical copies of chromosomes are separated into ___________________. ______________ _____________________ occurs, producing _____________ __________________ cells.


 Importance of Crossing Over

_____________________________ - Exchange of corresponding segments of DNA during meiosis, when pairs of homologous chromosomes are held tightly together.


Crossing over results in:



This acts as a ________________________________________________________________, which allows ___________________ ____________________ to occur.



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