Humans produce two types of gametes:
Sperm (male) formed by spermatogenesis
Ovum/egg (female) formed by oogenesis
Spermatogenesis (in testes)
Occurs in seminiferous tubules of testes.
Starts at puberty and continues throughout life.
Diploid cells (spermatogonia, 2n) undergo meiosis haploid sperm (n).
One spermatogonium produces 4 sperm cells.
Sperm structure: head (nucleus + acrosome), middle piece (mitochondria), tail (movement).
Oogenesis (in ovaries)
Begins before birth; primary oocytes remain arrested until puberty.
After puberty, one egg matures every menstrual cycle.
One primary oocyte forms 1 ovum + 3 polar bodies.
Ovulation releases the mature egg from ovary into fallopian tube.
2. Fertilization
Fertilization is the fusion of male and female gametes.
Occurs in the ampulla of fallopian tube.
Sperm penetrates egg using enzymes from acrosome.
Fusion of nuclei forms zygote (diploid, 2n).
Determines genetic makeup and sex of the baby (XX = female, XY = male).
3. Embryo Development
Cleavage
Zygote undergoes rapid mitotic divisions forms 2-cell, 4-cell, 8-cell stages.
Forms a solid ball called morula.
Blastocyst Formation
Morula becomes blastocyst with:
Inner cell mass (forms embryo)
Outer trophoblast (forms placenta)
Implantation
Blastocyst attaches to uterine wall (endometrium).
Placenta develops for nutrient, gas, and waste exchange between mother and fetus.
Gastrulation & Organogenesis
Three germ layers form:
Ectoderm skin, nervous system
Mesoderm muscles, bones
Endoderm internal organs
Organs begin to develop embryo becomes fetus.
4. Pregnancy (Gestation)
Lasts about 9 months (40 weeks).
Fetus grows and develops inside uterus.
Ends with parturition (childbirth).
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