Exercise 13:Reproduction Meiosis Spermatogenesis Oogenesis Ovarian cycle Uterine cycle Fertilization Embryonic and fetal development

Meiosis the process of nuclear division within a cell that involves in a reduction of chromosome number from diploid to haploid, resulting in gamete formation Human somatic (body) cells have 46 chromosomes 22 pairs of autosomes and 2 sex chromosomes XX in females, XY in males Human gametes (sex cells – eggs and sperm) have 23 chromosomes Sperm cells carry either an X or a Y

Meiosis Of the 46 chromosomes, there are 23 kinds - 2 copies of each kind One copy from mother, one from father, coming together when a sperm fertilizes an egg The 2 copies are called homologous chromosomes – they carry the same genes (although they might vary in the version – different alleles) Exception: X and Y, although paired in males, are not considered homologous

Meiosis First: review of mitosis Prior to mitosis Replication of DNA 46 chromosomes all copied Each copy = chromatid ‘sister’ chromatids held together at centromere

Replicated chromosome

Review of Mitosis Stages of mitosis Prophase: chromosomes condense and nuclear membrane breaks down; mitotic spindle forms Metaphase: chromosomes align at equator Anaphase: chromosomes divide Telophase: chromosomes unpack; nuclear membranes reassemble

Review of Mitosis

Stages of Meiosis Prior to meiosis: DNA replication, resulting in 46 chromosomes each with 2 sister chromatids held together at centromeres Meiosis occurs in 2 phases: Meiosis I: Reduction division Separation of homologous chromosomes Chromosome number now 23 Each chromosome still has 2 sister chromatids Meiosis II: Mitotic division Separation of sister chromatids

Meiosis I In Prophase I, the homologous chromosomes pair up This ensures that each daughter cell winds up with exactly one copy of each of the 23 kinds The sister chromatids of the 2 chromosomes make 4 total copies of each DNA strand – a tetrad While paired up, they entwine (synapsis) and can break and reform, swapping parts (chiasmata and crossing over)

Stages of Meiosis I synapsis chiasma www.bioethics.gov/.../stemcell/appendix_a.html chiasma

Stages of Meiosis I www.bioethics.gov/.../stemcell/appendix_a.html

Stages of Meiosis II

Products of Meiosis Four daughter cells Haploid (23 chromosomes) Each has one copy of each kind of chromosome Identical, except for 2 things: In males, half X, half Y sex chromosomes Crossing over results in different combinations of alleles

Spermatogenesis

Testis: Low Power Seminiferous tubules: spermatogenesis Interstitial cells: produce testosterone

Spermatogenesis

Spermatogenesis

Spermatogenesis

Oogenesis

Ovary Ovarian cycle Follicles secrete estrogens and house egg Follicular stage Luteal stage Follicles secrete estrogens and house egg Primordial Primary Secondary Mature

Ovarian Cycle

Ovary: Low Power

Ovary: Early stages

Ovary: Mature Follicle

Ovary: Mature Follicle structures

Ovary: Corpus Luteum

Ovary: Corpus Luteum

Uterine cycle Corresponds with Ovarian Cycle Menstrual phase Synchronized by ovarian hormones Menstrual phase Proliferativie phase Corresponds to ‘diestrous’ in other mammals Secretory phase Corresponds to ‘estrous’ in other mammals

Uterus: Diestrous

Uterus: Diestrous

Uterus: Estrous

Uterus: Estrous

Embryonic and fetal development EmbryologyReproduction.ppt