Nondisjunction And Chromosomal Abnormalities

25 July 2022
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Nondisjunction
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failure of homologous chromosomes or sister chromatids to separate properly during meiosis or mitosis
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Results of nondisjunction in Meiosis I
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all gametes have an abnormal number of chromosomes (ex. n+1 or n-1)
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Result of nondisjunction in meiosis II
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Half of gametes have normal number of chromosomes, other half have abnormal number
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Aneuploidy
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Having an abnormal number of chromosomes. Chromosomal losses are more detrimental than chromosome gains.
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Trisomy
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A situation in which an otherwise diploid cell has three copies of a particular chromosome.
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Monosomy
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A situation in which an otherwise diploid cell has only one copy of a particular chromosome.
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Chromosome abnormalities
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Deviations from the normal chromosome number leading to problems.
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Causes of nondisjunction
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Older females have a higher chance of giving birth to a baby with Down syndrome bc their cell processes are not as controlled or precise as younger women.
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Down syndrome
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Trisomy of chromosome 21
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Klinefelter syndrome
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Extra X chromosome in males - XXY Symptoms: sterile
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Turner syndrome
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Monosomy of chromosome 23 in females - X Symptoms: sterile
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Metafemale
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Trisomy of chromosome 23 in females - XXX Symptoms: sterile
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Trisomy 13
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Patau syndrome - a chromosomal condition associated with severe intellectual disability and physical abnormalities in many parts of the body. Due to the presence of several life-threatening medical problems, many infants with trisomy 13 die within their first days or weeks of life. Only five percent to 10 percent of children with this condition live past their first year. Most cases of trisomy 13 result from having three copies of chromosome 13 in each cell in the body instead of the usual two copies. Trisomy 13 can also occur when part of chromosome 13 becomes attached (translocated) to another chromosome during the formation of reproductive cells (eggs and sperm) or very early in fetal development. Affected people have two normal copies of chromosome 13, plus an extra copy of chromosome 13 attached to another chromosome. Translocation of trisomy 13 can be inherited, but nondisjunction cannot.
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Deletion
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Region of a chromosome is deleted, meaning less genetic material. Symptoms: heart or kidney problems, sever facial abnormalities
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Duplication
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Extra copy of a region of a chromosome exists. Symptoms: severe intellectual disability
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Similarities between duplication and deletion and inversion
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Can occur by abnormal crossing-over
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Inversion
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Chromosome broken in 2 places and reconnected so that a region is flipped from the normal order.
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Simple translocation
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Single piece of one chromosome breaks off and is attached to another nonhomologous chromosome
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Reciprocal translocation
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Two chromosomes exchange pieces of different regions in nonhomologous chromosomes
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Similarities between translocation and inversion
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Do not change total amount of genetic material, can lead to overall deficiencies and duplications after meiosis.
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Similarities between translocations
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Occur between nonhomologous chromosomes
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