Results of Abnormal Meiosis

1. Results of Abnormal Meiosis Biology 30 TMSS Mrs. S. Pipke-Painchaud

2. Definitions • Karyotype: • a method used to organize the chromosomes of a cell in relation to number, size and type. • Human Karyotype: http://www.people.virginia.edu/~rjh9u/karyotyp.html • The Biology Project - Karyotyping activity: http://www.biology.arizona.edu/human_bio/activities/karyotyping/karyotyping.html • Google Image Search: http://images.google.ca/images?q=karyotype&hl=en

3. Chromosomal Mutations • “changes in genetic material that involve entire chromosomes or pieces of them” (Addison Wesley 157) • Types of Mutations: (structural) • DELETION: one or more genes is lost from the chromosome • ABCDE --> ABDE

4. DUPLICATION: during meiosis an unequal crossover occurs and it receives an extra copy from its partner chromosome. • ABCDE --> ABBCDE • TRANSLOCATION: a whole or an entire piece of a chromosome attaches to a different pair. • ABCDE --> ABCXYZDE

5. INVERSION: a piece of a chromosome breaks free, turns around and reattaches itself. • ABCDEFGHI--> ABCDIHGFE

6. Changing Chromosome Number • Nondisjunction: “failure of chromatids or chromosomes to separate during cell division” (Addison Wesley 158). • Nondisjunction: “failure of chromatids or chromosomes to separate during cell division” (Addison Wesley 158). • What happens when this occurs in Mitosis? Or Meiosis? Mitosis: cell dies, but the organism is not harmed Meiosis: production of an abnormal gamete; you are dealing with the production of sex cells and the possible creation of a new individual.

7. Abnormal Meiosis • Nondisjunction - mistakes sometimes occur during meiosis. This occurs when 2 homologous chromosomes move to the same pole during anaphase I. The resulting daughter cells either have one too many chromosomes or one less chromosome. Resulting Human Gametes: have 22 or 24 chromosomes. If fertilized by a normal cell they have 45 and 47 chromosomes.

8. When an abnormal gamete joins with a normal gamete . . . • Monosomy: “zygote receives only one of a particular type of chromosome instead of two, as a normal gamete would” (Addision Wesley 158). • The zygote has 45 chromosomes. • One less. (one homologous chromosome is missing its partner)

9. Trisomy: “the zygote receives three chromosomes of a particular type instead of two” (Addision Wesley 158). • Zygote has 47 chromosomes • One extra • Once these cells undergo mitosis, every cell there after will have an abnormal number of chromosomes.

10. In Humans: • Monosomies and trisomies that occur in embryos are lethal. • Down Syndrome (47, 21+) is an exception • autosomal trisomy (trisomy 21) • mild to severely disabled • almond shaped eyes • enlarged tongues • short stocky bodies • poor muscle development and coordination • possible heart defects • can lead active, productive lives. (A.W. 208)

11. Down Syndrome • Frequency of Down Syndrome births increase dramatically with the age of the mother. • Age 30 = 1/1000 • Age 40 = 1/100 • Why? • History of Down Syndrome: Trisomy 21 - the story of Down Syndrome • http://www.ds-health.com/trisomy.htm

12. Info from: National Institute of Child Health and Human Development http://www.nichd.nih.gov/publications/pubs/downsyndrome/down.htm

13. Cause: Random error at the 21st chromosome. • Cannot be inheritied • Familial Down Syndrome - 1 arm of the 21st chromosome is copied to one of the 21st pairs of chromosomes (translocation). This type can be inheritied.

14. Other Autosomal Trisomies • Patau Syndrome (47, 13+): • 1-2 per 10 000 • extra copy of the 13th chromosome • average survival 2.5 days • brain malformations, mentally challenged and heart problems • The fetus.net http://www.thefetus.net/page.php?id=1473

15. Edwards Syndrome (47, 18+): • 1 in every 6000-8000 live births • severely affects internal organs • less than 5% survive >1year • found more often in females • e-medicine: http://www.emedicine.com/ped/topic652.htm

16. Polyploidy • “nondisjunction occurs in all the pairs of chromosomes at once. A polyploidy organism has three or more entire sets of chromosomes.” (Addison Wesley 159). • In animals, it is lethal. • In plants, it can produce a stronger and more useful plant with larger flowers and fruit.

17. Can occur naturally or in a lab setting. • Approx. 25-50% of plant species are polyploid. (A.W. 159) • Triticum aestivum - wheat (bread) 42 chromosomes • originated 8000 years ago • a hybrid of ancient wheat (28) and wild grass (14) • Potatoes • Oats • ~ Addison Wesley 159 Other Examples

18. Back Polyploid Examples • Normal = 2n or diploid • Triploid (3n) - sterile • potatoes (larger), bananas (soft seeds - wild bananas have hard seeds), seedless water melons • Tetraploid (4n) • alfalfa, coffee, peanuts, Macintosh Apples, white potato, tobacco, cotton • Others: • Octaploid Strawberries, Oats (6n)

19. Polyploidy in animals • although most often fatal examples do exist in some insects, fish, amphibians and reptiles. • Only one mammalian examples exists: Argentinean Rat (4n = 102) • http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Polyploidy.html • some salmon, African Frogs (MadSci.nethttp://www.madsci.org/posts/archives/Apr2003/1049863034.Cb.r.html

20. Nondisjunction of the Sex Chromosomes • Turner’s Syndrome (45, X): • monosomy • born female, short, webbed neck, broad shield like chest • 1 in 3000 female births • normal in childhood, normal intelligence. • Adolescence: never reach normal height, do not develop sexually and are sterile. (A.W. 209) • Turner Syndrome Society: http://www.turner-syndrome-us.org/resource/faq.html

21. Klinefelter Syndrome (47, xxy) • Trisomy; 1 in 700 • tall, male, sterile • underdeveloped testes, can cause some feminine features (I.e. body shape, breast development) (A.W. 208) • can also karyotype 48 XXXY; 48XXYY; 49 XXXXY • y chromosome determines maleness; absence of y = female (Turner’s Syndrome) • may be some developmental delays (especially in the area of language) (National Institute of Health - http://www.nichd.nih.gov/publications/pubs/klinefelter.htm#xwhat)

22. Defective Chromosome Structure • Cri-du-chat Syndrome: • significant deletion from chr 5 • baby’s cry sounds like a cat’s meow • small heads • severely developmentally disabled • rarely live past 1 or 2 • (A.W. 209) • 1 in 20 000 to 50 000 births (Genetics Home Reference: http://ghr.nlm.nih.gov/condition=criduchatsyndrome#definition

23. Single Allele Disorders • Gene Mutations: (point mutations) • mutations of a single gene because of small errors in the sequence of or number of nucleotides which cause a change in amino acids. • GGU --> GGU • CCA --> CAA

24. Recessive Genetic Disorders • Tay Sachs Disease: • fatal; inability to break down a lipid; causes an accumulation in the brain = blindness, then seizures • death occurs within the first year of life • higher rate in Ashkenzai Jews (Central Europe) • (A.W. 210)

25. Cystic fibrosis: • mutation that causes an excessive amount of mucous to be released by the pancreas, lungs and other organs. • Leads to blocked digestive tract, congested lungs and other pnemonia like infections • No treatment = death at early age • Treatment can prolong life until adulthood

26. Dominant Allele Disorders • Are less common . . . Why? • Because individuals die before reproducing • Huntington’s Disease: • fatal disorders that results in deterioration of the brain and nervous system • symptoms appear in later 30s and early 40s • already passed gene onto children • (A.W. 211) Other Dominant Alleles

27. Codominant Disorders • Sickle Cell Disease • Hemoglobin A = Normal • Hemoglobin S = Sickle Cell • both are codominant • an attack begins with a lack of oxygen, HemS cells form long chains. The RBC become sickle shaped and tangle. The clumped cells will clog capillaries and stop blood flow. Sickling crisis is very painful and may cause death. • High incidence in Africa and the Middle East because being heterozygous offers some resistance to malaria. (A.W. 211-212)

28. Is it possible to have anXY female or an XX male? • Yes • on the Y chromosome there is an SRY Region (Sex Determining Region), which is responsible for male development. If this regions gets translocated to an X it will cause Maleness. • XY Female - SRY region is missing • XX Male - SRY region translocated to X

29. Autosomal vs Sex Chromosome Trisomies • In 1961, Mary Lyon proposed that early on in development of a normal female, one X chromosome in each body cell is inactivated. • She suggested the inactive X chromosome was the darkly staining mass, called a Barr Body that normally appears in the nuclei of female cells.

30. Thus, one reason sex chromosomes trisomies are less disruptive is because all of the extra X chromosomes are inactivated except for a few active genes. • Example: Calico and Tortoise Shell cats are always female. WHY? - Heterozygous - X inactivation is random - one X (Orange) one X (Black); where ever an orange X is inactivated the black will show. If the Black X is inactivated the orange color will show. When the cells go through mitosis and grow, the cat develops patches of black fur and patches of orange fur.

31. Examples of Dominant Alleles • Dimples • freckles • widow’s peak • farsightedness • broad lips • polydactyly (extra digits) Back

32. Why does it increase with the mother’s age? • All primary oocytes are formed by birth • once ovulation begins each succeeding oocyte has been stopped in meiosis for a progressively longer period of time • older primary oocyte means a greater chance of deterioration or exposure to other harmful elements. Back

33. Other Genetic Disorders • Color Blindness (Sex Linked) • Muscular Dystrophy • Hemophilia (Sex Linked)