Exercise 13:Reproduction Meiosis Spermatogenesis Oogenesis Ovarian cycle Uterine cycle Fertilization...
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Transcript of Exercise 13:Reproduction Meiosis Spermatogenesis Oogenesis Ovarian cycle Uterine cycle Fertilization...
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
Stages of Meiosis I
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– 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– 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