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chromosomal abnormalities in humans PPT .pptx
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- 2. • These arethread like structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes. • Humans have 23 pairs of chromosomes, with one chromosome from each parent. The chromosomes are coiled up DNA. • Twenty-two of the pairs are autosomes, and one pair, number 23, is the sex chromosomes. Any variation from this pattern causes abnormalities. What are chromosomes?
- 12. • Under normalconditions all of the chromosomes are inherited intact. This is a normal karyotype of human chromosomes. • The karyotype can help identify abnormalities in the structure or the number of chromosomes. • A karyotype is an individual’s complete set of chromosomes. • A karyotype may be used to look for abnormalities in chromosome number or structure. • These newer methods compare the patient's DNA to a normal DNA sample. The comparison can be used to find chromosomal abnormalities where the two samples differ.
- 15. • Syndrome characterizedby malformations or malfunctions in any of the body’s systems, and caused by abnormal chromosome number or constitution are called chromosomal disorders. • A chromosome from any of the pairs may be duplicated (trisomy) or absent (monosomy); • an entire set of 23 chromosome pairs can be duplicated three (triploidy) or more (polyploidy) times; • or one arm or part of one arm of a single chromosome may be missing (deletion). • Part of one chromosome may be transferred to another (translocation), which has no effect on the person in which it occurs but generally causes a deletion or duplication syndrome in his or her children. • Changes in chromosome number occur during sperm or egg formation or in the early development of the embryo. • In the latter case, a mixture of cells, some normal (euploid) and some containing abnormal chromosome complements, may occur, a condition known as mosaicism. Chromosomal disorder
- 16. • Sometimes chromosomalabnormalities arise in the early stages of an embryo, sperm, or infant. A mother's age is one of the many environmental factors that might lead to genetic abnormalities. • Some diseases require a gene change to be inherited from both parents for the disease to occur. This type of testing usually is offered to people who have a family history of a specific inherited disease or who belong to certain ethnic groups that have a higher risk of specific inherited diseases.
- 17. Chromosomal abnormalities reasons: •when there is an error 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. One cell with 46 chromosomes divides and becomes two cells with 46 chromosomes each. This kind of cell division occurs throughout the body, except in the reproductive organs. This is the way most of the cells that make up our body are made and replaced. • Meiosis results in cells with half the number of chromosomes, 23, instead of the normal 46. This is the type of cell division that occurs in the reproductive organs, resulting in the eggs and sperm.
- 19. • In bothprocesses, the correct number of chromosomes is supposed to end up in the resulting cells. However, errors in cell division can result in cells with too few or too many copies of a chromosome. Errors can also occur when the chromosomes are being duplicated. • Other factors that can increase the risk of chromosome abnormalities are: • Maternal Age: Women are born with all the eggs they will ever have. Some researchers believe that errors can crop up in the eggs' genetic material as they age. • Older women are at higher risk of giving birth to babies with chromosome abnormalities than younger women. Because men produce new sperm throughout their lives, paternal age does not increase risk of chromosome abnormalities.
- 20. • Environment: Althoughthere is no conclusive evidence that specific environmental factors cause chromosome abnormalities, it is still possible that the environment may play a role in the occurrence of genetic errors.
- 22. Autosomal Numerical abnormality •An abnormal number of chromosomes is known as aneuploidy , and occurs when an individual is either missing a chromosome from a pair (resulting in monosomy) or has more than two chromosomes of a pair (trisomy, tetrasomy, etc.). • Aneuploidy can be full, involving a whole chromosome missing or added, or partial, where only part of a chromosome is missing or added. Aneuploidy can occur with sex chromosomes or autosomes.
- 23. • An exampleof monosomy in humans is Turner syndrome, where the individual is born with only one sex chromosome, an X. • Rather than having monosomy, or only one copy, the majority of aneuploid people have trisomy, or three copies of one chromosome. An example of trisomy in humans is Down syndrome, which is a developmental disorder caused by an extra copy of chromosome 21; the disorder is therefore also called trisomy 21.
- 33. Sperm aneuploidy • Exposureof males to certain lifestyle, environmental and/or occupational hazards may increase the risk of aneuploid spermatozoa. In particular, risk of aneuploidy is increased by tobacco smoking, and occupational exposure to benzene, insecticides , and perfluorinated compounds. Increased aneuploidy is often associated with increased DNA damage in spermatozoa.
- 34. Structural autosomal abnormalities •When the chromosome's structure is altered, this can take several forms: • Deletions: A portion of the chromosome is missing or has been deleted. Known disorders in humans include Wolf–Hirschhorn syndrome, which is caused by partial deletion of the short arm of chromosome 4; and Jacobsen syndrome, also called the terminal 11q deletion disorder. • Duplications: A portion of the chromosome has been duplicated, resulting in extra genetic material. Known human disorders include Charcot–Marie–Tooth disease type 1A, which may be caused by duplication of the gene encoding peripheral myelin protein 22 (PMP22) on chromosome 17. • Inversions: A portion of the chromosome has broken off, turned upside down, and reattached, therefore the genetic material is inverted. • Insertions: A portion of one chromosome has been deleted from its normal place and inserted into another chromosome.
- 35. • substitution mutation:A substitution mutation is a type of replication error during DNA replication which places the wrong nucleotide or sequence of nucleotides in the wrong position. A type of substitution mutation, a point mutation, occurs which a single nucleotide is substituted. This can be seen in the image below. • Ex Sickle-Cell Anemia, Color Blindness
- 39. Translocations: A portionof one chromosome has been transferred to another chromosome. There are two main types of translocations: Reciprocal translocation: Segments from two different chromosomes have been exchanged. Robertsonian translocation: An entire chromosome has attached to another at the centromere - in humans, these only occur with chromosomes 13, 14, 15, 21, and 22.
- 41. • Rings: Aportion of a chromosome has broken off and formed a circle or ring. This happens with or without the loss of genetic material. • Isochromosome: Formed by the mirror image copy of a chromosome segment including the centromere.
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