(a)+Chromosomes

** __CHROMOSOMES__ **

** What are Chromosomes? **


 * Chromosomes are structures made up of tightly coiled-up DNA and proteins, located inside the nucleus in cells. These chromosomes are passed on from parents to offspring, carrying the genetic information. Human nucleus contains 23 pairs of chromosomes, 22 autosomes and 1 pair of sex chromosomes. **

Not even under a microscope, chromosomes are not visible in the cell's nucleus when the cell isn't dividing. Nevertheless, chromosomes becomes visible under a microscope when DNA that make up the chromosomes becomes more tightly packed during cell division. Most knowledge of of chromosomes was learned by researchers observing chromosomes during cell division.

The short arm of the chromosom is labeled the "p arm." The long arm of the chromosome is labeled the "q arm."

Special stains can be used to display the contents in the nucleus. As the cell begins to divide, the contents appear as a series of thread-like structures. As the threads shorten, they take up the stain, hence they are called 'chromosones' (literally 'colored-bodies'). Genes are short sections of DNA when a chromosone is divided. Each gene carries coded information for the production of a protein by the cell.

Analogy: Chromosomes are like birth certificates, driver licences or social security cards as they hold important information about the citizens/people like chromosomes hold crucial genetic information for the human body.

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** The structure of chromosomes : **


 * **In Eukaryotic cells (e.g. human, animals, plants)**

**Each chromosome consists of two chromatids attached by one centromere, which holds the two chromatids together until they separate. The chromatids are made up of tightly coiled DNA around proteins called histones, which help in the tight packing of DNA.**
 * **In Prokaryotic cells (e.g. bacteria)**

**Chromosomes are simpler; their DNA exists as a loop in a single chromosome. Usually it is a single loop, but often there are extra circles called plasmids. It is dispersed within the cell. It is not enclosed by a separate membrane.**

**__What are X and Y Chromosomes?__ **

The **XY sex-determination system** is the sex-determination system found in humans and most other mamals. In this system, females have two of the same kind of sex chromosome (XX), and are called the homogametic sex. Males have two distinct sex chromosomes (XY), and are called the heterogametic sex. When they reproduce, if it's a female then she will have XX chromosomes and if its a male, it will have XY chromosomes. However, an opposite scheme is found in birds.  ﻿ This is how the XY sex determination system works: 

 



media type="youtube" key="lUESmHDrN40?version=3" height="390" width="640" <span style="color: #d7630f; font-family: 'Comic Sans MS',cursive; font-size: 130%;">This YouTube video shows the structure of a Chromosome to DNA in animation.

<span style="color: #1eae29; font-family: 'Comic Sans MS',cursive; font-size: 210%;">__** KARYOTYPES **__

<span style="background: white; color: #d7630f; font-family: 'Comic Sans MS',cursive; font-size: 130%; line-height: normal; margin: 0in 0in 0pt;">Karyotypes are the pictures of chromosomes in the nuclei of any animal. The Karyotypes are always organized in an order, called the 'homologous pairs' (chromosome pairs having the same length, same straining pattern etc. One homologous chromosome is from the mother and the other is from the father). Karyotypes are arranged in order of decreasing size.


 * <span style="background: white; color: #d7630f; font-family: 'Comic Sans MS',cursive; font-size: 130%; line-height: normal; margin: 0in 0in 0pt;">Female Karyotypes: **

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<span style="background: white; color: #000000; font-family: 'Comic Sans MS',cursive; font-size: 130%; line-height: 0px; margin: 0in 0in 0pt; overflow: hidden;">Male Karyotypes:

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<span style="color: #d7630f; font-family: 'Comic Sans MS',cursive; font-size: 130%; margin: 0in 0in 0pt;">** Uses of Karyotyping: **

<span style="color: #d7630f; font-family: 'Comic Sans MS',cursive; font-size: 130%; margin: 0in 0in 0pt 27pt; tabstops: list .5in; text-indent: -0.25in; vertical-align: middle;">**1. Studying evolution**: Because of the huge variation in karyotypes in replication and transcription, and even the variant between the number of chromosomes in different species, evolution can be studied by comparing two sets of karyotypes in different species. However, this study is still very new. <span style="color: #d7630f; font-family: 'Comic Sans MS',cursive; font-size: 130%; margin: 0in 0in 0pt 27pt; tabstops: list .5in; text-indent: -0.25in; vertical-align: middle;">**2. Identifying/classifying species (taxonomy):** each species have different numbers of karyotypes and different variations. <span style="color: #d7630f; font-family: 'Comic Sans MS',cursive; font-size: 130%; margin: 0in 0in 0pt 27pt; tabstops: list .5in; text-indent: -0.25in; vertical-align: middle;">**3. Identifying chromosomal disorders**: may include extra or missing chromosomes (etc. extra sex chromosomes XXY), or extensions and deletions in chromosomes. This is done by comparing a normal karyotype with the subject's karyotype. <span style="color: #d7630f; font-family: 'Comic Sans MS',cursive; font-size: 130%; margin: 0in 0in 0pt 27pt; tabstops: list .5in; text-indent: -0.25in; vertical-align: middle;">**4. Identifying genetic disorders**: Chromosomal disorders may lead to genetic disorders, and may be passed onto offspring. <span style="color: #d7630f; font-family: 'Comic Sans MS',cursive; font-size: 130%; margin: 0in 0in 0pt 27pt; tabstops: list .5in; text-indent: -0.25in; vertical-align: middle;">**5. Studying inheritance of chromosomes**: a child's karyotype is a combination of the parents' karyotypes. <span style="color: #d7630f; font-family: 'Comic Sans MS',cursive; font-size: 130%; margin: 0in 0in 0pt 27pt; tabstops: list .5in; text-indent: -0.25in; vertical-align: middle;">**6. To determine the characteristics and sex of a child before birth**: by looking at the sex chromosomes <span style="color: #d7630f; font-family: 'Comic Sans MS',cursive; font-size: 130%; margin: 0in 0in 0pt 27pt; tabstops: list .5in; text-indent: -0.25in; vertical-align: middle;">**7. To study cellular functions**

<span style="color: #d7630f; font-family: 'Comic Sans MS',cursive; font-size: 130%; margin: 0in 0in 0pt 27pt; tabstops: list .5in; text-indent: -0.25in; vertical-align: middle;">media type="youtube" key="BjX90u1pVnM?version=3" height="390" width="640"

**This Youtube Video is a brief overview of Karyotyping.**
<span style="color: #d7630f; font-family: 'Comic Sans MS',cursive; font-size: 130%; margin: 0in 0in 0pt; tabstops: list .5in; text-indent: -0.25in; vertical-align: middle;">** Work Cited: **

<span style="font-family: 'Comic Sans MS',cursive;">CancerQUest. "YouTube - Broadcast Yourself." //Chromosome to DNA//. Youtube, 30 July 2007. Web. 25 Apr. 2011. [].

<span style="font-family: 'Comic Sans MS',cursive;">Dorsey. "Chromosomes." //Contexo. Info//. None. Web. 26 Apr. 2011. [].

<span style="font-family: 'Comic Sans MS',cursive;">"Structure of a Chromosome." //Think Quest//. 1999. Web. 27 Apr. 2011. <http://library.thinkquest.org/28751/review/division/1.html>.