SEXUAL REPRODUCTION

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

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

SPERMATOGENESIS

SPERMATOGENESIS

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

SPERMATOGENESIS

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

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

OOGENESIS

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)

MULTIPLE BIRTHS

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

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

INDEPENDENT ASSORTMENT

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

CROSSING OVER

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

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

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

ERRORS DURING MEIOSIS CHANGES IN CHROMOSOME STRUCTURE

ERRORS DURING MEIOSIS CHANGES IN CHROMOSOME STRUCTURE

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

ERRORS DURING MEIOSIS CHANGES IN CHROMOSOME NUMBER Non-disjunction

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

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

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

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

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

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

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

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

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

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

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

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

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

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