What is a Chromosome?

Lying in the Nucleus of the cell are genetic structures called Chromosomes which contain DNA. For different species, there are different number of chromosomes. In humans for example, there are 46 chromosomes or 23 pairs (44 autosomal and 2 sex)

Below is a diagram of a chromosome.

(Pickering 189)

LIst of organisms by chromosomes
Aquatic bat
92 (largest number of chromosomees out of the mammal family)
Swamp Wallabies
10 for male, 11 for female

Chromosomes structure
Below is a video about the structure of chromosomes.

(Chromosome to DNA)

Chromosomes are several threadlike bodies, that carry the genes in a linear order. The human species have 23 pairs, that are designated 1 to 22 in order of decreasing size. Chromosomes are basically made up of DNA, wrapped around some proteins, in the cells. As you can see in the video, a strand of DNA makes up a chromosome.

Below is a diagram of the structure of a chromosome
(Structure of Chromosomes)
Karyotype is a visual representation of all chromosomes of one cell of an individual. We use karyotype for humans for many purposes such as to check for “chromosome abnormalities”, study cellular function, taxonomic relationship and to study about the evolutionary events in the past (Fergus).
How are karyotypes made?
A karyotype is made by taken a sample from an individual (usually blood sample) to collect white blood cells and through a process, a visual presentation is created. Here’s how, once the sample has been collected, the people in charge must be sure that the white blood cells are actively dividing, they then separate the cells to take what they need, after comes the growing stage where cells are cultured for a few days then synchronized. To be able to create a karyotype, the chromosomes must be visible therefore out of their cells; this is the next step. We then stain the chromosomes so that they are visible enough to be read, then finally, the final analysis of the karyotype.
Most humans have a standard Karyotype. Most of the human karyotypes contain 22 pairs of autosmal and a pair of sex chromosmes. In some organisms there are special changes that occur in the karyotype during the development. In some species there are large eliminations of heterochromatin and in others there are small visual adjustments to the karyotype. Some of these differences are stated below:
  • Chromosome elimination; this is when entire chromosomes are eliminated from the karyotype during the development
  • Chromosome Diminution; this is when some of the chromosomes are set aside in some particular cells
  • X-inactivation; This is when some of the x chromosomes do not get activated.

There are 6 things that are usually looked at in a karyotype and the following is the list:
  • Differences in the absolute sizes of chromosomes
  • Differences in the position of centromeres.
  • Differences in relative size of chromosomes.
  • Differences in the basic number of chromosomes.
  • Differences in number and position of satellites
  • Differences in degree and distribution of heterochromatic regions. (What is a Karyotype)

This is an example of karyotype.
(About Angelman Syndrome)

Karyotypes are also used to spot any genetic disorders or abnormality. We know that the person has no genetic disorders when he or she has 46 chromosomes. However, we know that a person has a genetic disorder when the person has:
  • Too many or too few chromosomes: when the sperm and the egg cell does not have equal numbers of chromosomes.
  • Missing pieces: when genetic material is broken off or missing from the chromosome

The diagram below shows where in the chromosome lies the different parts of the chromosome, and other abnormalities that can occur:


An example of a chromosome abnormality that can be found using a karyotype test is Trisomy 21. This is when the person have three number 21 chromosomes (1 more than usual), which causes Down syndrome (Fergus). Below is a karyotype that shows Trisomy 21.
(Karyotype with Trisomy 21)
NONDISJUNCTION is when there are too many or too few chromosomes. Normally, during meiosis, the type of cell division that produces sex cells, each cell recieves one of each choromosome. During fertilization (when the egg and sperm fuse together) the zygote recieves two copies of each choromosome. This is the normal number which provides proper development. If the choromosomes are not distributed correctly into the two daughter cells, than one daughter cell will have twice the number of copies of that chromosome, and the other daughter cell will have none. This is called NONDISJUNCTION. If these cells are fertilized, they result in abnormalities in the offspring such as down's syndrome, Turner's syndrome (when there are too little chromosomes), and Klinefelter's syndrome (when there are too many chromosomes).
However, a majority of the time, an embryo with an incorrect number of chromosomes won't survive and then the pregnant person has a miscarriage. This can happen early enough during the pregnancy that the woman may not even know she is pregnant. 50% of the miscarriages during the first-trimester are results of chromosomal abnormalities.
Work cited:

"About Angelman Syndrome - Testing 101." Foundation for Angelman Syndrome Therapeutics. Web. 17 Oct. 2011. <http://www.cureangelman.org/what-testing101.html.>

Chromosome to DNA . You Tube. N.p., n.d. Winship Cancer Institute, 30 July 2011. Web. 27 Oct. 2011. ,[[http://www.youtube.com/‌watch?feature=player_embedded&v=lUESmHDrN40.]]

"Chromosomes | Define Chromosomes at Dictionary.com." Dictionary.com | Find the Meanings and Definitions of Words at Dictionary.com. Web. 20 Oct. 2011. <http://dictionary.reference.com/browse/Chromosomes.>

"Chromosomal Abnormalities." March of Dimes. Web. 27 Oct. 2011.

"Designer Genes: Karyotypes." D. W. Brooks Site. Web. 25 Oct. 2011.

Fergus, Kathleen. “Karyotype.” About.com. N.p., n.d. Web. 21 Oct. 2011.

"Karyotype - What Is a Karyotype." Down Syndrome - Information on Causes, Care and Resources for Down Syndrome Families. Web. 17 Oct. 2011. <http://downsyndrome.about.com/od/downsyndromeglossary/g/karyotypedef_ro.htm.>

"Karyotype Test - What Is a Karyotype Test and How Is It Done." Down Syndrome - Information on Causes, Care and Resources for Down Syndrome Families. Web. 22 Oct. 2011.

Karyotype with Trisomy 21. N.d. Learn. Genetics. N.p., n.d. Web. 21 Oct. 2011.
Pickering, Ron. Complete Biology. Oxford: OUP Oxford, 2009. Print.

Levitan, Denise A., Rita Nanda, Janet D. Rowley, and Olufunmilayo Olopade. "Recurring Chromosome Rearrangements in Human Cancer - Holland-Frei Cancer Medicine - NCBI Bookshelf." NCBI. Web. 27 Oct. 2011. http://www.ncbi.nlm.nih.gov/books/NBK13639/.

“Structure of Chromosomes.” TutorVista.com. N.p., n.d. Web. 18 Oct. 2011. [[http://www.tutorvista.com/‌content/‌biology/‌biology-ii/‌heredity-and-evolution/‌structure-chromosomes.php.]]

"Using Karyotypes to Predict Genetic Order." Learn.Genetics. N.p., n.d. Web. 19 Oct. 2011.
<http://learn.genetics.utah.edu/content/begin/traits/ predictdisorder/>.

"What Is a Chromosome? - Genetics Home Reference." Genetics Home Reference - Your Guide to Understanding Genetic Conditions. Web. 27 Oct. 2011.

“What is a Karyotype?” Innovate Us. N.p., n.d. Web. 21 Oct. 2011.