7.3.2: Chromosomal Disorders
- Page ID
- 228144
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- Explain how structural changes and errors during cell division can result in chromosomal abnormalities.
- Describe the impact of advanced maternal age on chromosomal disorders.
Chromosomal Disorders
Types of Structural Changes
- Deletion occurs when part of a chromosome is lost or deleted.
- Inversion occurs when a section of a chromosome breaks off, flips around, and then reattaches in the opposite direction.
- Duplication occurs when a section of a chromosome is repeated.
- Translocation occurs when part of one chromosome breaks off and attaches to another chromosome.
Figure \(\PageIndex{1}\): Types of Mutations. Image by kingmaxton8 is in the public domain.
Advanced Maternal Age as a Risk Factor
Autosomal Chromosome Disorders
| Disorder | Description |
|---|---|
| Down Syndrome/Trisomy 21 | Caused by an extra chromosome 21 and includes a combination of birth defects. Affected individuals have some degree of intellectual disability, characteristic facial features, often heart defects, and other health problems. The severity varies greatly among affected individuals. |
| Trisomy 9 Mosaicism |
Caused by having an extra chromosome 9 in some cells. The severity of effects relates to the proportion of cells with extra chromosomes. The effects include fetal growth restriction resulting in low birth weight and multiple anomalies, including facial, cardiac, musculoskeletal, genital, kidney, and respiratory abnormalities. |
| Trisomy 13 | Caused by an extra chromosome 13. Affected individuals have multiple birth defects and generally die in the first weeks or months of life. |
| Trisomy 18 |
Sex-Linked Chromosomal Disorders
| Disorder | Description | |
|---|---|---|
| Turner Syndrome (XO) |
It occurs when all or part of one of the X chromosomes is lost before or soon after conception due to a random event. The resulting zygote has an XO composition. Turner Syndrome affects cognitive functioning and sexual maturation in girls. Infertility and short stature may be noted. | Affects about 3% of all female babies conceived. |
| Klinefelter Syndrome (XXY) | It occurs when an extra X chromosome is present in a male's cells due to a random event. The Y chromosome stimulates the growth of male genitalia, but the additional X chromosome inhibits this development. The male can have some breast development, infertility, and low levels of testosterone. |
1 in 500-1,000 male births |
| XYY Syndrome | It occurs when an extra Y chromosome is present in a male's cells. There are a few symptoms. They may include being taller than average, acne, and an increased risk of learning problems. The person is generally otherwise normal, including normal fertility. |
1 in 1,000 male births |
| Triple X Syndrome (XXX) |
It occurs when an extra X chromosome is present in a female's cells. It may result in being taller than average, learning difficulties, decreased muscle tone, seizures, and kidney problems. | 1 in 1,000 female births |
| Fragile X Syndrome | It occurs when the body cannot make enough of a protein it needs for the brain to grow, causing problems with learning and behavior. It is caused by an abnormality in the X chromosome, which then breaks. If a female has Fragile X, her second X chromosome is usually healthy, but males with Fragile X don’t have a second healthy X chromosome. This is why symptoms of Fragile X are usually more serious in males. | 1 in 4,000 males 1 in 8,000 females |
References, Contributions and Attributions
Lifespan Development: A Psychological Perspective by Martha Lally and Suzanne Valentine-French is licensed under CC BY-NC-SA 3.0
2.1: Heredity by Paris, Ricardo, Raymond, & Johnson is licensed CC BY 4.0.