When this condition results from monosomy X , the chromosomal abnormality occurs as a random event during the formation of reproductive cells (eggs and sperm) in the affected person’s parent. An error in cell division called nondisjunction can result in reproductive cells with an abnormal number of chromosomes.
Where does nondisjunction occur in Turner syndrome?
Nondisjunction may occur during meiosis I or meiosis II. Aneuploidy often results in serious problems such as Turner syndrome, a monosomy in which females may contain all or part of an X chromosome. Monosomy for autosomes is usually lethal in humans and other animals.
What type of mutation causes Turner syndrome?
Turner syndrome is caused by partial or complete loss (monosomy) of the second sex chromosome. Chromosomes are found in the nucleus of all body cells. They carry the genetic characteristics of each individual and they come in pairs.
How does Turner syndrome develop?
Turner syndrome occurs when part or all of an X chromosome is missing from most or all of the cells in a girl’s body. A girl normally receives one X chromosome from each parent. The error that leads to the missing chromosome appears to happen during the formation of the egg or sperm.
How does meiosis affect Turner syndrome?
Turner syndrome (TS) is a complex developmental disorder in individuals with short stature who possess a 45,X cell line, with or without mosaicism. Since the single X chromosome is maternally derived in 80%, the genesis of the 45,X karyotype is due to instability of the Y chromosome leading to its loss during meiosis.
Does Turner syndrome occur in mitosis or meiosis?
In the case of Turner syndrome, it would appear that paternal meiosis (when the short arm of the X chromosome and Y chromosomes pair) involves greater risk than maternal meiosis that normal separation will fail, with subsequent loss of the X or Y chromosome.
Why does Nondisjunction occur?
Nondisjunction occurs when chromosomes fail to segregate during meiosis; when this happens, gametes with an abnormal number of chromosomes are produced.
Is Turner syndrome a dominant or recessive trait?
Turner syndrome only occurs in females. Noonan syndrome, sometimes inappropriately called male Turner syndrome, can occur in males or females. It is an autosomal dominant genetic disorder and is not a chromosomal disorder.
Why do only females get Turner syndrome?
The condition only occurs in females. Most commonly, a female with Turner syndrome has only 1 X chromosome. Others may have 2 X chromosomes, but one of them is incomplete. Sometimes, a female has some cells with 2 X chromosomes, but other cells have only 1.
How does mosaic Turner syndrome occur?
Mosaic Turner syndrome is also not inherited. In an affected individual, it occurs as a random event during cell division in early fetal development. As a result, some of an affected person’s cells have the usual two sex chromosomes, and other cells have only one copy of the X chromosome.
Is Turner syndrome caused by aneuploidy?
Turner syndrome is caused by having a missing or incomplete X chromosome.
How does Down syndrome occur?
Down syndrome results when abnormal cell division involving chromosome 21 occurs. These cell division abnormalities result in an extra partial or full chromosome 21. This extra genetic material is responsible for the characteristic features and developmental problems of Down syndrome.
Which characteristic is commonly associated with Turner syndrome?
Turner syndrome can affect: Appearance. Features of Turner syndrome may include a short neck with a webbed appearance, low hairline at the back of the neck, low-set ears, hands and feet that are swollen or puffy at birth, and soft nails that turn upward. Stature.
How does Down syndrome occur in meiosis?
In translocation, a piece of chromosome or a whole chromosome breaks off during meiosis and attaches itself to another chromosome. The presence of an extra part of the number 21 chromosome causes the features of Down syndrome.
Which process would cause Nondisjunction if it occurred during meiosis quizlet?
Nondisjunction can occur during anaphase of meiosis I or meiosis II. If it happens during meiosis I, an entire bivalent migrates to one pole (Figure 8.22a). Following the completion of meiosis, the four resulting haploid cells produced from this event are abnormal.
What happens during nondisjunction in meiosis?
Nondisjunction occurs when homologous chromosomes or sister chromatids fail to separate during meiosis, resulting in an abnormal chromosome number.