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Chromosomes taken from parents to produce the gender of child |
A chromosome abnormality reflects an abnormality of chromosome number or structure. There are many types of chromosome abnormalities. However they can be organized into two basic groups:
Numerical Abnormalities
A number abnormality occurs when an individual is missing either a chromosome from a pair (monosomy) or has more than two two chromosomes of a pair (trisomy).
Structural Abnormalities
When the chromosome’s structure is altered, it can take several forms:
- Deletions- A portion of the chromosome is missing or deleted.
- Duplications- A portion of the chromosome is duplicated, resulting in extra genetic material
- Translocation- When a portion of one chromosome is transferred to another chromosome
- Inversions- A portion of the chromosome has broken off, turned upside down and reattached, therefore the genetic material is inverted.
- Rings- A portion of a chromosome has broken off and formed a circle or ring. This happens with or without loss of genetic material
Most chromosome abnormalities occur as an accident in the egg or sperm. Therefore, the abnormality is present in every cell of the body. Some abnormalities, however, can happen after conception, resulting in mosaicism, where some cells have the abnormality and some do not.
Chromosome abnormalities can be inherited from a parent (such as a translocation) or be "de novo" (new to the individual). This is why chromosome studies are often performed on parents when a child is found to have an abnormality.
What is the difference between Normal and Abnormal sex chromosomes?
NORMAL SEX CHROMOSOMES | ABNORMAL SEX CHROMOSOMES |
- Two distinct gametes fuse to form a zygote - The zygote is diploid- contains two sets of chromosomes - Male gametes or sperm cells (humans/ other mammals)- are heterogametic- contain one of two types of sex chromosomes (X or Y) - Female gametes or eggs- contain only the X sex chromosomes and homogametic- sperm determines sex of individual | - Abnormal number of chromosomes (anuploidy) - Zygote has additional chromosome ( three instead of two)- it is trisomic. - Zygote is missing a chromosome- it is monosomic. - Male- Klinefelter syndrome is a disorder in which males have an extra X. Thought to be taller and overly aggressive. - Female- Turner syndrome affects females. If you have this syndrome it is also called monosomy X- genotype of only one X chromosome (XO) |
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Normal Sex Chromosomes in both MALE and FEMALE |
The following table includes information on sex chromosome abnormalities, resulting syndromes, and expressed physical traits.
Sex Chromosome Abnormalities | |||
Genotype | Gender | Syndrome | Physical Traits |
XXY, XXYY, XXXY | Male | Klinefelter Syndrome | Infertility, small testicles, breast enlargement |
XO | Female | Turner Syndrome | Sex organs don’t mature at adolescence, infertility, short stature |
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How chromosomes happen |
Chromosome abnormalities usually happen when there is a fault in cell division. There are two kinds of cell division: Mitosis and Meiosis.
- Mitosis: Results in two cells that are duplicates of the original cell.
- Meiosis: Results in cells with half the number of chromosomes, 23 instead of normal 46. These are eggs and sperms.
In mitosis and meiosis, the correct number of chromosomes is supposed to end up in the resulting cells. However, with the error of cell division it can result in cells to have too few or too many copies of a chromosome. Faults can also occur when the chromosomes are being doubled.
What failures can develop of testes in an XY person?
The failures that can develop of testes in an XY person is the development of testes depending of a number of genes. One of these genes is on the Y chromosome, another is on the X chromosome and several are on various autosomes (non-sex chromosomes). If any of these genes is missing or non-functioning, then the fetus will develop streak gonads" instead of testes. The streak gonads lack both germ cells and hormone-producing cells. They consist only of the fibrous tissue that normally supports the ovaries. This condition is known as Swyer syndrome.
What problems can occur with the body’s ability to produce testosterone?
The problems that can occur with the body’s ability to produce testosterone is being insensitivity of the body to luteinizing hormone, which is produced by the pituitary gland which stimulates the Leydig cells in the testes to develop and produce testosterone. This is called either Leydig cell hyperplasia or luteinizing hormone insensitivity.
Testosterone synthesis can also be interfered with by failure of a number of enzymes needed for testosterone synthesis. There are a number of enzymes involved.
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