A chromosome is a rod shaped structure within the animal cell which carries the stretches of DNA referred to as genes. They are located in pairs within the nucleus of the cell and determine the sex and the characteristics of the organism inherited from its parents. In the human species there are 46 chromosomes arranged in sets of 23 pairs, one set being donated by the mother and one by the father.
The sex cells are referred to as gametes; the male gamete being the spermatozoa, and the female gamete being the egg or ova. Commonly there is no problem associated with chromosomal crossing over during gamete formation but occasionally things go amiss and cause an alteration in the number of chromosomes in the nucleus or the internal gene structure within the chromosome becomes changed in some way.
Sometimes an extra chromosome can be embodied in the divided cell during gamete formation in which case on of the gamete cells will have a double copy of the same chromosome, and another gamete cell will be short of that particular chromosome. This is referred to as a nondisjunction.
Some Diseases Caused by Chromosome Disorders.
Chromosomal nondisjunction is not uncommon in humans and can often develop into the fatality of the fetus, but children can be born with the following disorders.
Down Syndrome. With this type of genetic disorder the child is born with a broad head accompanied by blunted facial features. The child is often short in height and has severe difficulty in learning. It is the most common type of chromosomal disorder and occurs because the baby receives 47 chromosomes instead of the usual 46 chromosomes. This is due to the presence of an extra copy of chromosome 21. The characteristics of the disorder can often show in the forms of dementia, slow physical and mental development, and increased rates of disease associated with the thyroid gland and intestines. If conception takes place in a 35 – 40 year old female then the risk of delivering a child suffering from Down syndrome is relatively high.
Patau Syndrome. This syndrome is a result of trisomy in chromosome 13. It seems to affect female babies more than male, but perhaps this is due to affected male fetuses dying in the womb. The child often suffers neurological problems and physical defects such as having extra fingers or toes, facial defects (cleft lip or palate), and serious heart defects.
Klinefelter’s Syndrome. This chromosomal disorder is known as the XXY condition. The female is characterized by the XX chromosome and the male by the XY chromosome. In Klinefelter’s syndrome the male has an XXY chromosome. It is estimated that about one male in every five hundred is affected by the condition which shows as the male having body proportions which closely resemble that of the female, and having small non sperm producing testes. Males can have multiple copies of the X chromosome (XXXY) or even (XXXXY) and the female characteristics become more pronounced with every increase in the number X chromosomes.
The sex cells are referred to as gametes; the male gamete being the spermatozoa, and the female gamete being the egg or ova. Commonly there is no problem associated with chromosomal crossing over during gamete formation but occasionally things go amiss and cause an alteration in the number of chromosomes in the nucleus or the internal gene structure within the chromosome becomes changed in some way.
Sometimes an extra chromosome can be embodied in the divided cell during gamete formation in which case on of the gamete cells will have a double copy of the same chromosome, and another gamete cell will be short of that particular chromosome. This is referred to as a nondisjunction.
Some Diseases Caused by Chromosome Disorders.
Chromosomal nondisjunction is not uncommon in humans and can often develop into the fatality of the fetus, but children can be born with the following disorders.
Down Syndrome. With this type of genetic disorder the child is born with a broad head accompanied by blunted facial features. The child is often short in height and has severe difficulty in learning. It is the most common type of chromosomal disorder and occurs because the baby receives 47 chromosomes instead of the usual 46 chromosomes. This is due to the presence of an extra copy of chromosome 21. The characteristics of the disorder can often show in the forms of dementia, slow physical and mental development, and increased rates of disease associated with the thyroid gland and intestines. If conception takes place in a 35 – 40 year old female then the risk of delivering a child suffering from Down syndrome is relatively high.
Patau Syndrome. This syndrome is a result of trisomy in chromosome 13. It seems to affect female babies more than male, but perhaps this is due to affected male fetuses dying in the womb. The child often suffers neurological problems and physical defects such as having extra fingers or toes, facial defects (cleft lip or palate), and serious heart defects.
Klinefelter’s Syndrome. This chromosomal disorder is known as the XXY condition. The female is characterized by the XX chromosome and the male by the XY chromosome. In Klinefelter’s syndrome the male has an XXY chromosome. It is estimated that about one male in every five hundred is affected by the condition which shows as the male having body proportions which closely resemble that of the female, and having small non sperm producing testes. Males can have multiple copies of the X chromosome (XXXY) or even (XXXXY) and the female characteristics become more pronounced with every increase in the number X chromosomes.
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