1. SEXUAL REPRODUCTION

2. GAMETE FORMATION
Products of meiosis in humans are haploid gametes (sperm and egg)
We call these processes:
Spermatogenesis
Oogenisis

3. SPERMATOGENESIS Meiosis: in the testes
From birth, males possess spermatogonium (2n)
During puberty, spermatogonia reproduce by mitosis
Resulting cells undergo meiosis
Forms 4 haploid cells (n)
Haploid cells undergo final development to develop into mature sperm

4. SPERMATOGENESIS

5. SPERMATOGENESIS

6. SPERMATOGENESIS
Sperm: Head region: contain nucleus and other important structures Midsection: contain many mitochondria Tail: flagellum

7. SPERMATOGENESIS

8. OOGENESIS Meiosis: in the ovaries Oogonium are produced before birth
Before birth, oogonia reproduce by mitosis and begin meiosis but stop at prophase I

9. OOGENESIS
During puberty, meiosis will continue for one cell each month
- Unequal division of cytoplasm
- Cell with most cytoplasm after first division continues through to meiosis II to form a viable egg
- Other cell is a polar body (will degenerate)
4. Following fertilization, meiosis II is completed to produce the mature egg and polar body
- haploid nucleus of egg fuses with haploid nucleus of sperm to create a diploid zygote

10. OOGENESIS

11. MULTIPLE BIRTHS FRATERNAL TWINS
When two eggs are released and both are fertilized
IDENTICAL TWINS
- Single zygote divides into two separate bodies in the first few days of development (genetically similar)

12. MULTIPLE BIRTHS

13. IMPORTANCE OF MEIOSIS Genetic Variation comes from:
Independent Assortment
Crossing Over

14. INDEPENDENT ASSORTMENT
Recall: Metaphase I aligns homologous chromosomes at the equatorial plate - Chromosomes of maternal and paternal origin are oriented toward different poles at random ** Resulting cells have a mixture of maternal and paternal cells

15. INDEPENDENT ASSORTMENT

16. CROSSING OVER
Recall: Prophase I allows non-sister chromatids of homologous chromosomes to exchange pieces of chromosome - Can occur at several points for one homologous pair ** Resulting chromosomes are now a mixture of maternal and paternal genes

17. CROSSING OVER

18. ERRORS DURING MEIOSIS
Independent assortment and crossing over provide potential for chromosomal abnormalities Many of the errors produce gametes that are not viable Some errors allow gametes to survive and fertilize - Since all body cells result from the zygote, they will all contain the error

19. ERRORS DURING MEIOSIS Chromosomal Errors:
Changes in chromosome structure
Changes in chromosome number

20. ERRORS DURING MEIOSIS CHANGES IN CHROMOSOME STRUCTURE
Deletion: piece of chromosome is deleted
Duplication: section of chromosome is repeated two or more times in a row
Inversion: section of chromosome is inverted
Translocation: segment of one chromosome becomes attached to a different chromosome

21. ERRORS DURING MEIOSIS
CHANGES IN CHROMOSOME STRUCTURE

22. ERRORS DURING MEIOSIS
CHANGES IN CHROMOSOME STRUCTURE

23. ERRORS DURING MEIOSIS CHANGES IN CHROMOSOME NUMBER
Non-disjunction: when homologous pairs or sister chromatids do not separate as they should during meiosis
- Anaphase I: homologous chromosomes do not separate so one entire pair is pulled to same pole
- Anaphase II: sister chromatids do not separate so both chromatids are pulled to the same pole

24. ERRORS DURING MEIOSIS
CHANGES IN CHROMOSOME NUMBER
Non-disjunction

25. ERRORS DURING MEIOSIS
Types of Genetic Disorders Associated with Chromosome Number
Down Syndrome: Trisomy 21
- Incidence increases with maternal age
- Intellectual diability, almond shape
eyes, flattened face, short stature

26. ERRORS DURING MEIOSIS
Types of Genetic Disorders Associated with Chromosome Number b) Edward Syndrome: Trisomy 18 - Intellectual and physical diability, facial abnormality, extreme muscle tone, early death

27. ERRORS DURING MEIOSIS
Types of Genetic Disorders Associated with Chromosome Number b) Edward Syndrome: Trisomy 18

28. ERRORS DURING MEIOSIS
Types of Genetic Disorders Associated with Chromosome Number
Patau Syndrome: Trisomy 13
- Intellecual and physical disabilities, defects in
organs, large triangular nose, early death

29. ERRORS DURING MEIOSIS
Types of Genetic Disorders Associated with Chromosome Number
Patau Syndrome: Trisomy 13

30. ERRORS DURING MEIOSIS
Types of Genetic Disorders Associated with Chromosome Number d) Turner Syndrome: XO - Type of monosomy - Short stature, webbed neck, sexually underdeveloped

31. ERRORS DURING MEIOSIS
Types of Genetic Disorders Associated with Chromosome Number d) Turner Syndrome: XO

32. ERRORS DURING MEIOSIS
Types of Genetic Disorders Associated with Chromosome Number
Triple X: XXX
- Tall, thin, menstrual irregularity

33. ERRORS DURING MEIOSIS
Types of Genetic Disorders Associated with Chromosome Number
Jacobs syndrome: XYY
- no unusual symptoms, taller than average

34. ERRORS DURING MEIOSIS
Types of Genetic Disorders Associated with Chromosome Number
Klinefelter Syndrome: XXY
- Sexual immaturity (cannot produce sperm) breast swelling

35. ERRORS DURING MEIOSIS
Types of Genetic Disorders Associated with Chromosome Number
Klinefelter Syndrome: XXY

36. PRENATAL GENETIC TESTING
Tests performed on a fetus to check for genetic based abnormalities
Commonly used for higher risk pregnancies:
Over 35 years old
Family history of genetic disorder
Other risk factors
Covered by OHIP

37. PRENATAL GENETIC TESTING
Non-Invasive Methods:
Blood Test: fetal proteins in mother’s blood are analyzed
Ultrasound: fetus is imaged and measurement of fluid at the back of the fetus’ neck

38. PRENATAL GENETIC TESTING
Invasive Methods:
Amniocentesis: collect sample of amniotic fluid which contains fetal cells
Chorionic Villus Sampling (CVS): Collect sample from part of placenta