CHROMOSOME DISORDER & THE
COMMON
TYPES
OF
TWO
CHROMOSOME
DISORDER
Sala Woo English 202C July 28th 2015 Audience & Purpose
The purpose of this document is to inform the audience about process and mechanism behind chromosome disorders and the different types of chromosome disorders. The audience for this description is for the general public that is familiar with some cell biology, such as college students that are majoring in Biology pursuing healthcare profession. Two specific types of chromosome disorders will be focused in this description: Turner Syndrome and Down Syndrome. Introduction
Chromosomes are genetic structures that are made of long threadlike strands of DNA containing specific information, giving living creatures their own genetic makeup. For example, they are responsible for our characteristic traits passed down from our parents. Every child is born with 46 chromosomes, 23 from the sperm cell, and 23 from the egg cell. One chromosome from each pair is a sex chromosome that determines the sex of the baby. Females normally have two X chromosomes (XX) and males normally have one X and one Y chromosome (XY).
However, there are cases when humans are born with abnormal number of chromosomes, which results in chromosome disorder. Chromosome disorders affect at least one in every 200 babies, having symptoms from birth or early childhood. However in some cases, the offspring do not survive the full term in the mother’s womb and is miscarried.
Chromosome Disorder
Chromosome disorder is a genetic disorder due a nondisjunction during meiosis I, meiosis II, or mitosis. Nondisjunction is the failure of chromosomes, or sister chromatids, to separate properly during cell division. When one sperm cell and egg cell contains 23 chromosomes each, they fuse during fertilization, and a zygote is produced. This zygote will start its cell division called meiosis and begin its development and maturation. Meiosis goes through two rounds of chromosomal division and each have 4 phases that make up the overall process. It is during Anaphase I or Anaphase II, where chromosomes fail to segregate properly, causing nondisjunction leading to a genetic disorder. As Figure 2 explains, If nondisjunction occurs during Anaphase I of meiosis I. it results with at least one ​
pair of chromosomes not segregating at the opposite side of the cells properly, resulting in one pair of gametes having an extra copy of chromosomes (2 chromatids) and one pair having one less. If nondisjunction occurs during Anaphase II of meiosis II, it results in at least one ​
pair of chromatids not segregating properly. Most of the time, with abnormal number of chromosomes, the resulting cell will not survive to produce new offspring. However, the individuals that do survive show symptoms or evidence of a syndrome that is either seen at birth or developed during early childhood. The two commonly known syndromes are Turner Syndrome, and the more common of the two, Down Syndrome. A diagnosis can be done either during a pregnancy via ultrasound, or a Karyotype, which is a test to identify and evaluate the number of chromosomes in a sample of body cells.
Down Syndrome
Down Syndrome is a chromosomal disorder resulting in intellectual disability and physical abnormalities, affecting male and female. Down syndrome is caused by an extra copy of chromosome 21. This occurs when the …. Down syndrome can be detected during an ultrasound or based on the abnormal levels of proteins found in the mother’s blood during the 15 to 16th week of pregnancy. ​
A firm diagnosis can be done with a karyotype for an extra copy of chromosome 21 or ​
trisomy 21​
. Children with Down syndrome often have heart defects. They have hearing loss and are prone to recurring ear infections. They are also prone to vision problems because of problems in their corneas and lenses. The joints in the neck may be unstable, which can lead to weakness or paralysis. Many people with Down syndrome develop thyroid disease (such as hypothyroidism) and diabetes. They are also at a higher risk of developing infections and leukemia. There is no known treatment or cure for Down syndrome. Turner syndrome
Turner syndrome is caused by the deletion of or partial formation of one of the two X chromosomes. This occurs during……. Turner syndrome occurs in about 1 out of 4,000 live female births and is the most common sex chromosome abnormality in females. However, 99% of affected fetuses abort spontaneously. Girls with Turner syndrome generally do not have menstrual periods (amenorrhea), and the breasts, vagina, and labia remain childlike rather than undergoing the changes of puberty. In 90% of girls, the ovaries are replaced by connective tissue and do not contain developing eggs (gonadal dysgenesis). A girl or woman with Turner syndrome is virtually always short compared with family members, and obesity is common. Many girls with Turner syndrome have attention­deficit/hyperactivity disorder and learning disabilities with difficulty assessing visual and spatial relationships, planning tasks, and paying attention. They tend to score poorly on certain performance tests and in mathematics, even if they achieve average or above­average scores on verbal intelligence tests. Intellectual disability is rare. Conclusion
There is no confirmed causes of chromosome disorders. However woman in their mid thirties have a 20 percent increase in their chances of giving birth to baby with a chromosome disorder as opposed to women in their twenties