Genetic Disorders - Principles Of Genetic Inheritance Patterns, Types Of Genetic Inheritance, Dominant And Recessive, Genetic Analysis
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Genetic disorders refer to medical conditions that develop as the result of abnormalities in an individuals genetic material, usually that is inherited. Inheriting or developing a genetic disorder leads to a collection of clinical manifestations known as a syndrome. These clinical manifestations can vary from person to person with the same genetic defect or have similar presentations.
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Genetic information is packaged into chromosomes that are found in thecells nucleus, or DNA containing organelle. Virtually every human cell has 46 chromosomes, except for the sperm and egg (reproductive cells) which each have 23 chromosomes. Fertilization of the egg by the sperm results in a newly formed cell called the zygote. Each zygote receives 23 chromosomes from the egg and 23 chromosomes f…
There are many types of genetic disorders. Mendelian disorders are a group of disorders that are inherited either as an autosomal (through one of the 44 chromosomes, excluding the X or Y chromosome) or X-linked (through the X chromosome) defect in a dominant or recessive pattern. Although most of them are commonly associated with inherited defects, many of them can involve spontaneous or de novo a…
A dominant gene means that a single allele can control whether the disease develops. If only one parents (usually affected) passes on an autosomal, defective gene which results in the child having a genetic disorder, then the disorder is called autosomal dominant. A recessive gene means that there is enough normal protein product to function properly from the normal gene and, therefore, two copies…
Chromosomal analysis can be performed on cell samples from an individual, a technique called karyotyping. A karyotype involves visualizing the chromosomes using a specific dye and a high-resolution microscope. The chromosomes can be distinguished from one another in size and staining pattern. Corresponding chromosomes 1 through 22 and the sex chromosomes can be lined up and visually inspected for …
If one parent has an autosomal dominant disease, then offspring have a 50% chance of inheriting that disease. There are roughly 2000 autosomal dominant disorders (ADDs) with effects that range from mild clinical manifestations to death. These diseases may develop early or late in life. ADDs include Huntington disease, Marfan syndrome (extra long limbs), achondroplasia (a type of dwarfism), some fo…
Recessive genetic disorders (RGD) result from inheriting two defective recessive alleles of a gene, one from each parent. RGD often require careful molecular or biochemical genetic analyses to determine carrier status. Hence, the birth of a child with a recessive disorder may surprise unknowing parents. The probability of two carrier or heterozygous parents having an affected child is 25% each tim…
X-Linked genetic disorders (XLGDs) can be either dominant or recessive. Dominant XLGDs affect females and males. Dominant XLGD's include: Albright's hereditary osteodystrophy (seizures, mental retardation, stunted growth), Goltz's syndrome (mental retardation), cylindromatosis (deafness and upper body tumors), oralfacial-digital syndrome (no teeth, cleft tongue, some mental re…
Statistics and twin studies are often used to determine the genetic basis for multi-factorial genetic disorders (MFGDs). Because environment can play an important role in the development of these diseases, identical and fraternal twins who have been raised in different homes are ideally studied. MFGD include some disorders associated with diet and metabolism, such as obesity, diabetes, alcoholism,…
The two most common aneuploidies, trisomies and extra sex chromosomes, can be due to maternal or paternal factors including advanced age. A number of aneuploidies can be attributed to dispermy, or when two sperm fertilizes one egg. The resulting genetic disorders can result in a spontaneous mutation. Live-born children with autosomal aneuploidies can have trisomy 13, 18, or 21, and all have some f…
Genetic tests are available and can reveal varying degrees of genetic information depending on the test. Most of these tests are performed by isolating chromosomes or by measuring a protein product that is excreted in the urine to test for biochemical defects. These tests can be used prior to conception to determine a couple's risk for having an affected child, during pregnancy, at birth or…
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