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Down Syndrome is a genetic disease that does not follow the traditional method of inheritance. Most people are familiar with the basics of this disease, but know very little about the details of this syndrome and its effects in humans. In this lesson we’ll learn about this disease, its symptoms, and its causes.

Genetic Diseases

A number of diseases are genetic. This means that the source of these diseases lies in the inherited traits and genes received from the mother and the father of the individual. These diseases are often the result of dominant/recessive inheritance, such as with sickle-cell anemia and cystic fibrosis. However, in some cases, genetic diseases may be caused by issues in the process of meiosis, or sex cell production. This lesson will discuss one of these diseases: Down Syndrome.

Meiosis and Down Syndrome

The human genome has 23 pairs of chromosomes (condensed DNA). This means that we have 46 chromosomes that provide the genetic information needed to make us who we are.

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In order for reproduction to occur, these chromosomes have to be divided in half in the sperm and egg cells of the parents. During this process, the pairs of chromosomes split so that only one of each pair will make it into the sperm or egg cell. When the egg and sperm cells unite, each pair is restored in the newly formed individual, and 23 pairs will now exist in the genome.Occasionally, however, this separation does not take place properly. In the event that pairs are not separated, it is possible that a person may receive an inappropriate number of chromosomes, such as three, where there should be only a pair. This condition is known as trisomy, and is the presence of three chromosomes in the portion of the DNA that should only have two.

Down Syndrome

Down Syndrome is also called trisomy 21. This name means that the 21st pair of chromosomes contains an additional copy. In genetics, having more than the normal number is often a problem, and in this case, it can cause many physical and mental symptoms. While not all symptoms of Down Syndrome are seen in all patients, several are relatively common.Down Syndrome leads to stunted growth in the individual. This is seen in 100% of the cases that have been evaluated globally.

Out of the many symptoms of this disease that exist, this one is the most common. Roughly 99% of the individuals with Down Syndrome will also demonstrate some mental development delays. It is important to note that a small number of individuals with Down Syndrome may be able to develop normal mental functions. Other common symptoms include weaker muscles, smaller genitalia, and small teeth.

While this is not a complete list of symptoms for this disease, these represent some of the most common ones that are exhibited.

Karyotype of Trisomy 21
Trisomy 21

Treatment for Down Syndrome

While there is no cure for Down Syndrome, researchers have developed ways to treat and manage the symptoms and signs of this disease. Early educational intervention allows for many individuals afflicted with Down Syndrome to obtain education and work in a job setting.

Occasionally, individuals with Down Syndrome may also attend college and receive higher educational and technical training. The key, however, is early intervention, meaning that professional help should be sought as soon as the child is born.For cognitive (mental) development, doctors often provide intervention as well. In many cases, this may include surgeries to help with hearing and therapy for speech development. Additionally, counseling may be used to assist with emotional development.

In almost all cases, these therapies may be effective, but will still result in delays compared to individuals without this disease.

Facts About Down Syndrome

A few interesting things to know about Down Syndrome:

  • The age of the mother is a primary factor in the inheritance of Down Syndrome. Older mothers are more likely to give birth to children with this disease.

  • The age of the father has also been shown to affect the incidence of Down Syndrome. Fathers over the age of 42 are more likely to have a child with Down Syndrome.
  • Down Syndrome was first identified in the 1860s by a scientist named John Down. He originally termed individuals with Down Syndrome mongoloid, referring to the facial features of individuals with the disease. This term is not currently used, and is considered an insult when used to describe individuals with this disease.

  • Until the 1970s, individuals with Down Syndrome were forced to be sterilized (which means they could not have kids). This was a part of the eugenics movement, which sought to cleanse the human population of any individuals that it considered inferior. Today, this process no longer takes place.

Learning Summary

Down Syndrome is one of the most notable genetic diseases. It is due to the 21st pair of chromosomes containing a third copy. While in most cases the effects can be very noticeable and development can be affected heavily, many individuals with this disease can live relatively normal lives through therapy and interventions.

Down Syndrome Key Terms ; Guide

Chromosomes play a role in Down Syndrome
  • Meiosis: sex cell production
  • Chromosomes: condensed DNA; humans have 23 pairs
  • Trisomy: The presence of three chromosomes instead of the usual pair
    • Trisomy 21: Another name for Down Syndrome since the 21st pair of chromosomes contains an extra copy
  • Symptoms: stunted growth (100%) and mental development delays (99%)
  • Causes: Age of mother (primary) and father
  • Treatment: Early education treatment, counseling, and surgery in some cases

Learning Outcomes

After finishing this lesson, you will be able to:

  • Define Down Syndrome and cite meiosis
  • Recall another name for Down Syndrome
  • Discuss the chromosome profile of an individual with Down Syndrome
  • Identify possible causes for the condition
  • List common symptoms and treatments of Down Syndrome

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