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Karyotypes

Karyotypes. A karyotype is an organized profile of a person's chromosomes. In a karyotype , chromosomes are arranged and numbered by size, from largest to smallest This arrangement helps scientists quickly identify chromosomal alterations that may result in a genetic disorder.

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Karyotypes

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  1. Karyotypes

  2. A karyotype is an organized profile of a person's chromosomes. • In a karyotype, chromosomes are arranged and numbered by size, from largest to smallest • This arrangement helps scientists quickly identify chromosomal alterations that may result in a genetic disorder

  3. To make a karyotype, scientists take a picture of someone's chromosomes, cut them out and match them up using size, banding pattern and centromere position as guides

  4. Homologous pairs are arranged by size in descending order (largest to smallest) with the sex chromosomes (XX for female or XY for male) as the last or 23 pair. Homologous chromosomes have genes for the same trait at the same location • Since humans have 46 chromosomes in their somatic or body cells, they have 23 pairs of chromosomes in their karyotype

  5. If chromosomes fail to separate in meiosis, a condition called nondisjunction, a person may have more or less than the normal 46 chromosomes on their karyotype.

  6. Chromosomal mutations can include changes in chromosome number • Nondisjunction occurs when the homologous chromosomes don’t separate properly during meiosis which creates offspring with more or less the 46 chromosomes

  7. Monosomyoccurs when an individual has only one of a particular type of chromosome • Turner syndrome(X0) is an example of monosomy

  8. Trisomyoccurs when an individual has three of a particular type of chromosome • Down Syndromeor Trisomy 21 where the individual has three 21st chromosomes; an example of trisomy

  9. Both monosomy & trisomy result when chromosomes fail to separate during meiosis; called nondisjunction • Monosomy and trisomy (aneuploidy) occur in plants and animals and may be lethal (deadly) • Polyploidy where the offspring have more than two sets of chromosomes occurs often in plants (3n, 4n ...)

  10. Cri du chat syndrome(results in retardation & a cat-like cry) is due to a deletion of a portion of chromosome 5

  11. Klinefelter's syndrome, 47XXY or XXY syndrome is a condition caused by a chromosomal nondisjunctionin males, and affected males are almost always sterile; an example of a trisomy

  12. Other Genetic Disorders • Fragile X Syndromecaused by an abnormal number of repeats (CCG) results in retardation & long, narrow face becomes more pronounced with age • Tay-Sachs (a disorder where the nervous system deteriorates) is a fatal gene mutation in Jewish people of Central European Descent

  13. Sickle cell anemia (red blood cells are C-shaped so can't carry as much oxygen) is an example of a gene mutation in African Americans; carrying the gene gives you an immunity (resistance) to malaria • Phenylketonuria or PKU occurs from the inability of a gene to synthesize a single enzyme necessary for the normal metabolism of phenylalanine and results in death

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