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Understanding Karyotypes and Nondisjunction in Genetics

Learn about karyotypes, which are pictures of chromosomes, and nondisjunction, a mutation leading to abnormal chromosome numbers. Discover how karyotyping helps determine genetic disorders like Down Syndrome and understand the impact of chromosomal abnormalities.

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Understanding Karyotypes and Nondisjunction in Genetics

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  1. Karyotypes and Nondisjunction

  2. KARYOTYPE: Definition • Picture of chromosomes taken during metaphase (mitosis) when chromosomes are fully condensed • Chromosomes are arranged large to small by homologous pairs • sex chromosomes shown last • Normal human karyotypes show 46 chromosomes • 44 autosomes (22 pairs of homologous chromosomes) • 2 sex chromosomes

  3. KARYOTYPE: Human Chromosomes

  4. KARYOTYPE: How it is useful • In order to study differences in size, shape, and chromosome number (too few or too many) • Determines the sex of the child • Usually done for humans when a known chromosomal disorder runs in family • (i.e. Down Syndrome) • Can be done for any organism

  5. NONDISJUNCTION:Definition and Results • Form of chromosomal mutation during meiosis when homologous chromosomes fail to separate • Results in abnormal number of chromosomes in gametes, which can possibly lead to a disorder in the offspring

  6. NONDISJUNCTION:Examples of Disorders • Down Syndrome – (autosome) - three copies of chromosome 21 • Karyotype shows 47 chromosomes (Trisomy 21) • Results in various degrees of mental disabilities, causes decrease immunities to diseases/organ defects, distinguished facial features • Edward’s Syndrome – (autosome) three copies of chromosome 18 • Karyotype shows 47 chromosomes (Trisomy 18) • Results in failure of all organ systems, death after a few months

  7. NONDISJUNCTION:Examples of Disorders • Turner’s Syndrome – (sex chromosome) – only one X chromosome is inherited • Karyotype 45, X • Results in sterile female, short in stature, heart and kidney defects • “Superfemale” – (sex chromosome) – extra X chromosome is inherited • Karyotype 47, XXX (Trisomy X) • Results in healthy, fertile female

  8. NONDISJUNCTION:Examples of Disorders • Klinefelter’s Syndrome – (sex chromosome) –extra X chromosome(s) is/are inherited • Karyotype 47, XXY (or even 48, XXXY; 49, XXXXY) • Usually results in sterile male • “Supermale” – (sex chromosome) – extra Y chromosome is inherited • Karyotype 47, XYY • Usually results in sterile, more violent, decreased intelligence, taller male

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