Also known as Down syndrome, trisomy 21 is a genetic condition caused
by an extra chromosome
. Most babies inherit 23 chromosomes from each parent, for a total of 46 chromosomes. Babies with Down syndrome however, end up with three chromosomes at position 21, instead of the usual pair.
What causes the most common chromosomal abnormality called trisomy 21 group of answer choices?
Most cases of
Down syndrome
are not inherited. When the condition is caused by trisomy 21, the chromosomal abnormality occurs as a random event during the formation of reproductive cells in a parent. The abnormality usually occurs in egg cells, but it occasionally occurs in sperm cells.
What is the most common cause of trisomy 21?
Trisomy 21.
About 95 percent of the time,
Down syndrome
is caused by trisomy 21 — the person has three copies of chromosome 21, instead of the usual two copies, in all cells. This is caused by abnormal cell division during the development of the sperm cell or the egg cell.
What kind of mutation causes trisomy 21 or Down syndrome?
TRISOMY 21 (
NONDISJUNCTION
)
Down syndrome is usually caused by an error in cell division called “nondisjunction.” Nondisjunction results in an embryo with three copies of chromosome 21 instead of the usual two. Prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to separate.
What causes chromosomal abnormalities trisomy?
Trisomy 18 and 13 are usually caused by
spontaneous genetic mutations that occur at the time of fertilization
. Normally, each egg and sperm cell contains 23 chromosomes. The union of these cells creates 23 pairs, or 46 total chromosomes, half from the mother and half from the father.
Is trisomy 21 more common in males or females?
Overall, the two sexes are affected roughly equally. The
male-to-female ratio
is slightly higher (approximately 1.15:1) in newborns with Down syndrome, but this effect is restricted to neonates with free trisomy 21.
What is life expectancy for Down syndrome?
What is the life expectancy for people with Down syndrome? The life expectancy of people with Down syndrome increased dramatically between 1960 and 2007. In 1960, on average, persons with Down syndrome lived to be about 10 years old. In 2007, on average, persons with Down syndrome lived to be
about 47 years old
.
What is the normal range of trisomy 21?
The cut-off values were as follows: Trisomy 21
≥ 1:270
; Trisomy 18 ≥ 1: 350, AFP MoM ≥2.50, high risk of ONTD [16]. Pregnant women with a high risk of Trisomy 21 and Trisomy 18 were advised to undergo karyotype analysis using the amniotic fluid cells in order to confirm the diagnosis.
Can a Down syndrome child look normal?
People with
Down syndrome all look the same
. There are certain physical characteristics that can occur. People with Down syndrome can have all of them or none. A person with Down syndrome will always look more like his or her close family than someone else with the condition.
Who does trisomy 21 affect?
Trisomy 21 is the most common chromosomal anomaly in humans, affecting
about 5,000 babies born each year and more than 350,000 people
in the United States.
Can you tell if a baby has Down syndrome in an ultrasound?
An
ultrasound can detect fluid at the back of a fetus’s neck
, which sometimes indicates Down syndrome. The ultrasound test is called measurement of nuchal translucency.
What makes you high risk for Down’s syndrome baby?
One factor that increases the risk for having a baby with Down syndrome is
the mother’s age
. Women who are 35 years or older when they become pregnant are more likely to have a pregnancy affected by Down syndrome than women who become pregnant at a younger age.
What is considered high risk for Down syndrome?
Patients are
more likely to have a baby with Down syndrome or another chromosome abnormality when they are age 35 or older
, or if they have already had a child with such an abnormality. These patients are considered “high-risk” and have additional testing options.
Can sperm cause chromosomal abnormalities?
An estimated 1 to 4 percent of a healthy male’s sperm have abnormal numbers of chromosomes, or aneuploidy, that are caused by
errors
during cell division (meiosis) in the testis.
Can chromosomal abnormalities be cured?
In many cases,
there is no treatment or cure for chromosomal abnormalities
. However, genetic counseling, occupational therapy, physical therapy and medicines may be recommended.
How can you prevent chromosomal abnormalities?
- See a doctor three months before you try to have a baby. …
- Take one prenatal vitamin a day for the three months before you become pregnant. …
- Keep all visits with your doctor.
- Eat healthy foods. …
- Start at a healthy weight.
- Do not smoke or drink alcohol.
