In genetics, what is a trisomy?

Answer 1

After the egg has been fertilized it begins to divide. In Metaphase of cell division the chromosomes line up on the equator and get ready for their migration to the poles of the cell. The problem occurs in the next phase, telophase, this is when the identical chromosomes are being pulled away to opposite ends, what happens is one pair of chromosomes gets stuck and do not seperate and both are pulled to one side of the cell. This is called non-disjunction. The most commonly known genetic disease in which this happens is Down's Syndrome, also known as Trisomy 21. The normal number of the #21 chromosome is supposed to be 2 but because of non-disjunction, one extra #21 gets copied.

Trisomy is a genetic diseased caused by non-disjunction of the chromosomes during Mitosis/Meiosis.

Answer 2

Trisomy is the term used to describe the presence of 3 copies of a single chromosome. Normally, there are only 2 copies of each chromosome. However, various intra- and extra-cellular situations result in Trisomy. The result of Trisomy (or any genetic condition) is altered production of the proteins for which those genes encode. The result of that is the phenotype, or the physical appearances.

Answer 3

Trisomy is the abnormal genetic condition where an individual inherits three copies of a particular chromosome. We have 23 Chromosomes and two copies of each. One derived from our father's sperm and the other form the mother's egg. Each pair of chromosomes are nearly identiacla with minor vaiations. These are the somatic chromosomes. One other chromosome pair are the sex chromosomes. A woman has two similar x chromosomes. but a male has one x chromosome and a much shoter y chromosome. The x and y chromosomes have some similar genetic sequences but many more that are unique to themselves.
The condition called trisomy is where a cell nucleas has three copies of a particular chromosome instead of the normal two..
Trisomy chromosome18 has already discussed. So let me mention trisomy in chromosome 21. This causes the devestatong genetic abnormalities of Down's syndrum. (once called "mongolism)".
Dan the Answers-Man

Answer 4

Any chromosome can have a trisomy. 21, 18, X AND 13 are the most common trisomies that are compatible with life. For example, a trisomy of a certain chromosome may cause so much of a mutation that the baby may have a trisomy but it isn't alive.

Answer 5

The presence of a single extra chromosome, yielding a total of three chromosomes of that particular type instead of a pair. Partial trisomy refers to the presence of an extra copy of a segment of a chromosome.

Answer 6

Trisomy 18 syndrome is a disorder of human chromosomes which occurs in approximately 1 in 6,000 live born infants. Trisomy 18 is due to the presence of an extra #18 chromosome. Over 90% of infants with Trisomy 18 syndrome will have a full trisomy while the remainder will have a trisomy due to a rearrangement called a translocation or have mosaicism (two different cell lines).

Infants born with Trisomy 18 usually have small size at birth. There is a recognizable pattern of physical features that often allow the health professional to make the diagnosis of the syndrome. These physical findings are not medically significant but provide clues. They include: prominence to the back part of the head, short eyelid fissures, small mouth and jaw, external ear variations, clenched fist with index finger overlapping the third and 5th finger overlapping the 4th, small fingernails, underdeveloped or altered thumbs, short sternum (breastbone), club feet and redundant skin at the back of the neck.

Synonyms: Trisomy 18

Edward Syndrome

Trisomy E

Trisomy 16-18

(these last two terms are usually not used at the present time)

Major impact of Trisomy 18 is a predisposition to congenital malformations (birth defects), increased infant mortality, and a developmental disability in older infants and children.

Birth Defects

The congenital malformations involve the medically and significant findings mentioned above as well as the presence of some internal or external birth defects. The most common and important is a defect of the heart. Over 90% of children with Trisomy 18 will have a congenital heart malformation; these include: ventricular septal defect – an opening between the lower chambers of the heart which prevents the heart from pumping blood correctly (a heart murmur is generally heard from this finding); atrial septal defect – an opening between the two upper chambers of the heart making it difficult for the heart to pump sufficient oxygen rich blood to body tissues (a heart murmur is often heard); patent ductus arteriosis – a heart defect involving the lack of closure of the channel that usually closes near the time of birth. This then is a persistence of the opening of this channel. In addition, children with Trisomy 18 usually have an alteration of one of the four heart valves. This combination is referred to as a ventricular septal defect with polyvalvular dysplasia. About 10% of children with Trisomy 18 will have a life threatening heart defect noted before or soon after birth. These include a double outlet right ventricle and hypoplastic left heart.

Medical Problems

The increased occurrence of infant mortality is related to a combination of factors but most importantly central apnea, where the brain does not give the message to breathe. Other complicating factors include difficulty feeding with aspiration with a predisposition to aspiration pneumonia, and under development of the lungs. The heart defects can play some role in this but are usually not the only cause of this increased mortality. Important and common birth defects seen in Trisomy 18:

Congenital heart defects 90%
Multiple joint contractures 10%
spina bifida
hearing loss >50%
radial aplasia (underdevelopment or missing radial bone of forearm) 5-10%
cleft lip 5-10%
birth defects of the eye 10%
Common Disorders in

Trisomy 18

feeding difficulties
gastroesophageal reflux
slow post natal growth
apnea
seizures
kidney defects
urinary tract infections
developmental disability
scoliosis
Routine follow-up of infants with Trisomy 18

Routine child care/anticipatory guidance
Cardiac evaluation
Eye evaluation
Hearing test
Infant/pre-school program early intervention
Ongoing Support
Routine ultrasound for Wilms tumor
Routine immunization
Referral for feeding clinic if appropriate
Scoliosis check

Answer 7

normally the chromosomes are paired. Trisomy is a third allele in what would normally be a pair.

Answer 8

Nothing more than an extra chromosome in the nucleus of the cell ... (three, versus two).

Answer 9

three copies of one chromosome, s/a down syndrome (3 #21)

Answer 10

I think its when the person has like an extra X chromosome. I THINK.