Hemophilia A & B are defected in:
a- X- linked dominant
b- X-linked recessive***
c- Y linked dominant
d- Y linked recessive.
---------------------------
Recessive gene linked to sex:
Sex-related diseases are transmitted from parents to children through one of the X or Y chromosomes. These are sex chromosomes.
Dominant inheritance occurs when an abnormal gene from one of the parents causes the disease, even if the compatible gene from the other parent is normal. The abnormal gene dominates.
However, in recessive inheritance, both compatible genes must be abnormal to produce the disease. If only one gene in the pair is abnormal, the disease does not occur or is mild. Someone who has an abnormal gene, but not the symptoms, is called a carrier. Carriers can transmit abnormal genes to their children.
Frequently, the term "sex-linked recessive" refers to X-linked recessive.
Information:
Recessive diseases linked to the X chromosome often occur in men. These have only one X chromosome, so a single recessive gene on that X chromosome will cause the disease.
The Y chromosome is the other half of the pair of XY genes in man. However, the Y chromosome does not contain most of the X chromosome genes. Because of this, it does not protect man. Diseases such as hemophilia and Duchenne muscular dystrophy occur as a result of a recessive gene on the X chromosome.
TYPICAL SCENARIOS:
In each pregnancy, if the mother is a carrier of a certain disease (she has only one abnormal X chromosome) and the father is not a carrier of the disease, the expected result is:
- 25% chance of a healthy male.
- 25% chance of a male with the disease.
- 25% chance of a healthy girl.
- 25% probability of a carrier girl without the disease.
If the father has the disease and the mother is not a carrier, the expected results are:
- 100% probability of a healthy male.
- 100% probability of a carrier girl without the disease.
RECESSIVE DISORDERS LINKED TO CHROMOSOME X IN WOMEN:
Women can acquire a recessive disorder linked to the X chromosome, but this is very rare. An abnormal gene on the X chromosome of each parent would be required, since a woman has two X chromosomes. This could occur in the following two scenarios:
In each pregnancy, if the mother is a carrier of the gene and the father has the disease, the expected results are:
- 25% chance of a healthy male.
- 25% chance of a male with the disease.
- 25% chance of a carrier girl.
- 25% chance of a girl with the disease.
If both the father and the mother have the disease, the expected results are:
- 100% probability that the child has the disease, whether boy or girl.
The probabilities of either of these two scenarios are so low that, sometimes, recessive diseases linked to the X chromosome are called "only male" diseases. However, this is not technically correct.
Female carriers may have a normal X chromosome that is abnormally inactivated. This is called "skewed X chromosome inactivation." These women may have symptoms similar to those of men or may have only mild symptoms.
a- X- linked dominant
b- X-linked recessive***
c- Y linked dominant
d- Y linked recessive.
---------------------------
Recessive gene linked to sex:
Sex-related diseases are transmitted from parents to children through one of the X or Y chromosomes. These are sex chromosomes.
Dominant inheritance occurs when an abnormal gene from one of the parents causes the disease, even if the compatible gene from the other parent is normal. The abnormal gene dominates.
However, in recessive inheritance, both compatible genes must be abnormal to produce the disease. If only one gene in the pair is abnormal, the disease does not occur or is mild. Someone who has an abnormal gene, but not the symptoms, is called a carrier. Carriers can transmit abnormal genes to their children.
Frequently, the term "sex-linked recessive" refers to X-linked recessive.
Information:
Recessive diseases linked to the X chromosome often occur in men. These have only one X chromosome, so a single recessive gene on that X chromosome will cause the disease.
The Y chromosome is the other half of the pair of XY genes in man. However, the Y chromosome does not contain most of the X chromosome genes. Because of this, it does not protect man. Diseases such as hemophilia and Duchenne muscular dystrophy occur as a result of a recessive gene on the X chromosome.
TYPICAL SCENARIOS:
In each pregnancy, if the mother is a carrier of a certain disease (she has only one abnormal X chromosome) and the father is not a carrier of the disease, the expected result is:
- 25% chance of a healthy male.
- 25% chance of a male with the disease.
- 25% chance of a healthy girl.
- 25% probability of a carrier girl without the disease.
If the father has the disease and the mother is not a carrier, the expected results are:
- 100% probability of a healthy male.
- 100% probability of a carrier girl without the disease.
RECESSIVE DISORDERS LINKED TO CHROMOSOME X IN WOMEN:
Women can acquire a recessive disorder linked to the X chromosome, but this is very rare. An abnormal gene on the X chromosome of each parent would be required, since a woman has two X chromosomes. This could occur in the following two scenarios:
In each pregnancy, if the mother is a carrier of the gene and the father has the disease, the expected results are:
- 25% chance of a healthy male.
- 25% chance of a male with the disease.
- 25% chance of a carrier girl.
- 25% chance of a girl with the disease.
If both the father and the mother have the disease, the expected results are:
- 100% probability that the child has the disease, whether boy or girl.
The probabilities of either of these two scenarios are so low that, sometimes, recessive diseases linked to the X chromosome are called "only male" diseases. However, this is not technically correct.
Female carriers may have a normal X chromosome that is abnormally inactivated. This is called "skewed X chromosome inactivation." These women may have symptoms similar to those of men or may have only mild symptoms.
Labels
Nursing questions