Transcript Nondisjunction Mutations - Point Pleasant Beach School
Nondisjunction Mutations
Chapter 12
• • • • Nondisjunction ("not coming apart") is the failure of chromosome pairs to separate properly during cell division.
This could arise from a failure of homologous chromosomes to separate in meiosis I , or the failure of sister chromatids to separate during meiosis II or mitosis. The result of this error is a cell with an imbalance of chromosomes. Such a cell is said to be aneuploid . Loss of a single chromosome (2n-1), in which the daughter cell(s) with the defect will have one chromosome missing from one of its pairs, is referred to as a monosomy . Gaining a single chromosome, in which the daughter cell(s) with the defect will have one chromosome in addition to its pairs is referred to as a trisomy .
• • • If these gametes are fertilized, it will result in an embryo in which all the cells have an abnormal chromosome # Great video demo here Narrated video here
Trisomy 21: Down syndrome
Down syndrome
• • • • • • • The condition is characterized by a combination of major and minor differences in structure. Often Down syndrome is associated with some impairment of cognitive ability and physical growth , and a particular set of facial characteristics. Down syndrome in a fetus can be identified with amniocentesis during pregnancy, or in a baby at birth.
Individuals with Down syndrome tend to have a lower than average cognitive ability, often ranging from mild to moderate developmental disabilities . A small number have severe to profound mental disability.
The incidence 1,000 births, although it is statistically much more common with older mothers.
of Down syndrome is estimated at 1 per 800 to http://en.wikipedia.org/wiki/Down_syndrome
Trisomy 18: Edwards syndrome
Edwards syndrome
• • • • • The incidence of the syndrome is estimated as one in 3,000 live births [2] . The incidence increases as the mother's age increases. The syndrome has a very low rate of survival, resulting from heart abnormalities, kidney malformations, and other internal organ disorders.
Only 50% of liveborn infants live to 2 months, and only 5–10% survive their first year of life.
http://en.wikipedia.org/wiki/Edwards_syndrome
Trisomy 13: Patau syndrome
Patau syndrome
• • • The risk of this syndrome in the offspring increases with maternal age at pregnancy, with about 31 years being the average.
[1] Patau syndrome affects approximately one in 10,000 live births.
A few symptoms are: – mental & motor challenged – polydactyly (extra digits) – microcephaly low-set ears – holoprosencephaly properly). (failure of the forebrain to divide – heart and kidney defects
XXY Klinefelter’s syndrome
Klinefelter’s syndrome
• • • • • The condition exists in roughly 1 out of every 1,000 males.
The principal effects are development of small testicles and reduced fertility . Some degree of language learning impairment may be present, [7] and neuropsychological testing often reveals deficits in executive functions .
[8] In adults, possible characteristics vary widely and include little to no signs of affectedness, a body type with some degree of (increased breast tissue).
lanky gynecomastia , youthful build and facial appearance, or a rounded http://en.wikipedia.org/wiki/Klinefelter%27s_syndrom e
Monosomy X: Turner’s syndrome
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Turner’s syndrome
Occurring in 1 out of every 2500 girls, the syndrome manifests itself in a number of ways. There are characteristic physical abnormalities, such as short stature , swelling , broad chest, low hairline, low-set ears , and webbed necks .
[3] Girls with Turner syndrome typically experience gonadal dysfunction (non-working ovaries ), which results in amenorrhea (absence of menstrual cycle) and sterility . Concurrent health concerns are also frequently present, including congenital heart disease , hypothyroidism (reduced hormone secretion by the thyroid ), diabetes , vision problems, hearing concerns, and many autoimmune diseases.
[4] Finally, a specific pattern of cognitive deficits is often observed, with particular difficulties in visuospatial, mathematical, and memory areas.
[5] http://en.wikipedia.org/wiki/Turner%27s_syndrome
XYY – Jacobs syndrome
• • • • • •
XYY
47, XYY boys have an increased growth velocity during earliest childhood, with an average final height approximately 7 cm above expected final height.
[3] Severe acne was noted in a very few early case reports, but dermatologists specializing in acne now doubt the existence of a relationship with 47,XYY.
[4] Testosterone levels (prenatally and postnatally) are normal in 47,XYY males.
[5] Most 47,XYY males have normal sexual development and usually have normal fertility. Since XYY is not characterized by distinct physical features, the condition is usually detected only during genetic analysis for another reason.
XYY boys have an increased risk of learning…and delayed speech and language skills. http://en.wikipedia.org/wiki/XYY
Prenatal detection
• • Amniocentesis: a small amount of amniotic fluid, which contains fetal tissues, is extracted from the amniotic sac surrounding a developing fetus, and the fetal cells (DNA) is examined for genetic abnormalities.
Can be performed between the 16th-20th week of pregnancy.
Prenatal detection
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