<meta http-equiv="refresh" content="1; url=/nojavascript/"> Chromosomal Disorders | CK-12 Foundation
Dismiss
Skip Navigation
You are reading an older version of this FlexBook® textbook: CK-12 Life Science Concepts For Middle School Go to the latest version.
%
Best Score
Practice Chromosomal Disorders
Practice
Best Score
%
Practice Now

Can you have too many chromosomes?

Yes, it's not a good thing to have extra chromosomes. An extra chromosome can be fatal to an embryo, in fact. In the case of a few chromosomes, however, a baby may be born with an extra chromosome. This child will have a chromosomal disorder.

Chromosomal Disorders

Some children are born with genetic defects that are not carried by a single gene. Instead, an error in a larger part of the chromosome or even in an entire chromosome causes the disorder. Usually the error happens when the egg or sperm is forming. Having extra chromosomes or damaged chromosomes can cause disorders.

Extra Chromosomes

One common example of an extra-chromosome disorder is Down syndrome ( Figure below ). Children with Down syndrome are mentally disabled and also have physical deformities. Down syndrome occurs when a baby receives an extra chromosome 21 from one of his or her parents. Usually, a child will receive one chromosome 21 from the mother and one chromosome 21 from the father. In an individual with Down syndrome, however, there are three copies of chromosome 21 ( Figure below ). Therefore, Down syndrome is also known as Trisomy 21.

A child with Down syndrome.

A child with Down syndrome.

Chromosomes of a person with Down Syndrome. Notice the extra chromosome 21.

Another example of a chromosomal disorder is Klinefelter syndrome , in which a male inherits an extra “X” chromosome. These individuals have an XXY genotype. They have underdeveloped sex organs and elongated limbs. They also have difficulty learning new things.

Outside of chromosome 21 and the sex chromosomes, most embryos with extra chromosomes do not usually survive. Because chromosomes carry many, many genes, a disruption of a chromosome can cause severe problems with the development of a fetus.

Damaged Chromosomes

Chromosomal disorders also occur when part of a chromosome becomes damaged. For example, if a tiny portion of chromosome 5 is missing, the individual will have cri du chat (cat’s cry) syndrome. These individuals have misshapen facial features, and the infant’s cry resembles a cat’s cry.

Vocabulary

  • Down syndrome : Chromosomal disorder that results when an embryo inherits an extra chromosome 21.
  • Klinefelter syndrome : Chromosomal disorder that results when a male inherits an extra “X” chromosome.

Summary

  • Changes in chromosome number can lead to disorders like Down syndrome.
  • Chromosomal disorders also occur when part of a chromosome becomes damaged.

Practice

Use the resources below to answer the questions that follow.

  1. Are all cases of Down Syndrome the result of inheritance?
  2. Do all cases of Down Syndrome have a complete extra chromosome? Explain your answer fully.
  3. Why are people with Down Syndrome at a greater risk for Alzheimer's Disease?
  1. What do all people diagnosed with a chromosome disorder share?
  2. What is a clinical geneticist? How are they different from a doctor? Think carefully about your answer.
  3. What is a karyotype?
  4. Do chromosomal disorders always involve extra genetic material?

Review

  1. Explain what causes Down Syndrome.
  2. How is a chromosomal disorder different from a genetic disorder.

Image Attributions

Description

Difficulty Level:

Basic

Grades:

7 , 8

Date Created:

Nov 29, 2012

Last Modified:

Jun 16, 2014
Files can only be attached to the latest version of Modality

Reviews

Please wait...
Please wait...
Image Detail
Sizes: Medium | Original
 
SCI.LSC.336.2.L.1

Original text