Mistakes in Meiosis

1. SBI 3U0 09/03/2011 Mistakes in Meiosis Karyotype Non-disjunction disorders (examples) Mutations (examples)

2. Karyotyping • a picture showing the number and type chromosomes in a cell • Chromosomes are arranged in order from largest to smallest • Shows major chromosomal abnormalities • i.e. pieces of chromosomes are missing of extra copies (will not show defective gene)

4. Preparation of a karyotype Fixative Packed red And white blood cells Hypotonic solution Blood culture Stain White Bloodcells Centrifuge 3 2 1 Fluid Centromere Sisterchromatids Pair of homologouschromosomes 4 5

5. Alternations of Chromosome Number • Non-disjunction (p. 116-118*) • Monosomy (i.e. Williams Syndrome) • Trisomy (i.e. Down`s Syndrome) • Abnormal Number of Sex Chromosomes (p. 363-364) (i.e. Turner Syndrome) • Mutations (p. 408-409) (i.e. Huntington`s Disease; Cystic Fibrosis; Leukemia)

6. Nondisjunctionin meiosis I Normalmeiosis II Gametes n + 1 n + 1 n – 1 n – 1 Number of chromosomes Non-Disjunction Alterations of Chromosome Number 1. Homologous chromosomes fail to move apart properly during meiosis 1

7. Alterations of Chromosome Number 2. Sister chromatids don't separate during meiosis II Normalmeiosis I Nondisjunctionin meiosis II Gametes n + 1 n – 1 n n Number of chromosomes

9. Alterations of Chromosome Number Monosomy – fertilized cell is missing a chromosome Trisomy – fertilized cell has an extra copy of a chromosome Ex. Down's Sydrome: 3 copies of chromosome # 21 (trisomy 21)

10. Alterations of Chromosome Number • Fertilization after nondisjunction in the mother results in a zygote with an incorrect number of chromosomes Eggcell n + 1 Zygote2n + 1 Spermcell n (normal)

11. Alterations of Chromosome Number – Example: Down syndrome is caused by an extra copy of chromosome 21 This karyotype shows three number 21 chromosomes

12. The chance of having a Down syndrome child goes up with maternal age • Down Syndrome occurs in about 1/700 live births.

13. Alterations of Chromosome Number • It is possible to have trisomy of chromosomes 13, 15, 18, 21 & 22 • This happens infrequently • Is it usually fatal if the embryo has trisomy of any of the other autosomal chromosomes • = spontaneous abortion

14. Abnormal Number of Sex Chromosomes

15. Poor beardgrowth Breastdevelopment Under-developedtestes • A man with Klinefelter syndrome has an extra X chromosome, genotype XXY

17. A woman with Turner syndrome lacks an X chromosome, genotype X0, or X. Characteristicfacialfeatures Web ofskin Constrictionof aorta Poorbreastdevelopment Under-developed ovaries

18. Mutations

19. Sickle Cell Anemia • Autosomal recessive blood disorder (ss) • Red blood cells have an abnormal “sickle” shape cause by an abnormal type of hemoglobin • Cells can clog up blood vessels • Caused by just one amino acid that is different from what it is supposed to be!

20. Cystic Fibrosis • Autosomal recessive mutation (cc) • Effects lungs - excessive mucus production • Breathing is very difficult

21. Huntington’s Disease • Autosomal dominant mutation (HH, Hh) – child of an affected parent has 50-100% chance of inheritance • Causes certain nerve cells in the brain to waste away or degenerate • Chromosome # 4 - causes a part of DNA to have a CAG repeat • Noticeable between age 30 – 40 years old

22. Homework Read pp. 358-362