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Biology – Lecture 56

Biology – Lecture 56. Karyotypes. Karyotype. The number and appearance of chromosomes in the nucleus of a eukaryotic cell. T he complete set of chromosomes in a species. Human Karyotype. What to Look For.

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Biology – Lecture 56

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  1. Biology – Lecture 56 Karyotypes

  2. Karyotype • The number and appearance of chromosomes in the nucleus of a eukaryotic cell. • The complete set of chromosomes in a species

  3. Human Karyotype

  4. What to Look For • Karyotypes describe the number of chromosomes, and what they look like under a light microscope. • Attention is paid to their length, the position of the centromeres, banding pattern, any differences between the sex chromosomes, and any other physical characteristics.

  5. How do they Look? • The chromosomes are arranged in pairs, ordered by size and position of centromere for chromosomes of the same size. • Sex Chromosomes are always last.

  6. Difference between Sex Chromosomes • X chromosomes are significantly larger than Y chromosomes.

  7. Human karyotype • The normal human karyotypes contain 22 pairs of autosomal chromosomes and one pair of sex chromosomes.

  8. Chromosome Pairs • There are 2 chromosomes of each number – one from the mom and one from the dad.

  9. How a karyotype is made • 1. Cells are blocked during mitosis. • 2. Chromosomes are taken from those cells and stained (making dark bands). • 3. Pictures of the chromosomes are taken, cut out and matched up according to size, banding pattern and centromere position.

  10. Interpreting a karyotype • Look at: • 1. the total number of chromosomes • 2. the sex chromosomes • 3. any extra or missing autosomal chromosomes

  11. Naming a Karyotype • 1. Count the total number of Chromosomes • 2. Name the sex chromosomes • 3. If there are extra chromosomes, name the placement of them after a + sign.

  12. Examples • 47, XY, +18 indicates that the patient has 47 chromosomes, is a male, and has an extra autosomal chromosome 18. • 46, XX is a female with a normal number of chromosomes • 47, XXY is a patient with an extra sex chromosome.

  13. Normal Human Karyotype • Females contain two X chromosomes and are denoted 46,XX; • Males have both an X and a Y chromosome denoted 46,XY. • Any variation from the standard karyotype may lead to developmental abnormalities.

  14. Developmental Abnormalities • In trisomy there is an extra chromosome resulting in three copies of the same chromosome. • In monosomy, there is a missing chromosome and the zygote will have one copy of that chromosome.

  15. How can cells end up with too many or too few chromosomes? • Sometimes chromosomes are incorrectly distributed into the egg or sperm cells during meiosis. When this happens, one cell may get two copies of a particular chromosome, while another cell gets none.

  16. How Does it Cause Abnormalities? • People who are born with an abnormal number of chromosomes often have genetic disorders because their cells contain too much or too little genetic information. • Scientists can predict genetic disorders by looking for extra or missing chromosomes in a karyotype.

  17. Common Abnormalities

  18. Turner’s Syndrome

  19. Kleinfelter’s Syndrome

  20. Down’s Syndrome

  21. Edward’s Syndrome

  22. Practice an X-linked Pedigree

  23. Practice an Autosomal Pedigree

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