Animal Reproduction

Asexual Reproduction Produced genetically identical individuals Examples: hydra, sponges

Sexual Reproduction Fusion of two haploid cells to form a diploid Meiosis produces haploid cells Mechanism to bring haploid cells together must be present Mechanism to create genetic diversity

Fertilization Haploid sperm and egg unite to form a diploid zygote

External Fertilization Sperm spread over egg cells Requires water Most aquatic animals Examples: most fish, corals, starfish Inefficient Spermatophore – sperm packaged into capsule Some terrestrial animals Examples: salamanders, scorpions, octopus

Internal Fertilization Requires copulation Most common method for terrestrial animals Less sperm and eggs needed

Human Reproduction

Male Reproductive Organs

Male Reproductive Organs Testes Sperm and testosterone Seminal vesicle Fructose and prostaglandin Prostate Basic fluid and sperm motility factors Bulbourethral gland Mucus

Testes Produce sperm and testosterone Spermatogenesis Spermatogonium – divides by mitosis Meiosis I Primary spermatocyte (2n)  secondary spermatocyte (1n) Meiosis II Secondary spermatocyte (1n)  spermatids (1n) Differentiation Spermatids (1n)  sperm (1n)

Testes

Spermatogenesis

Androgens – Male Sex Hormones Main androgen is testosterone Made by the Leydig cells of testes Purpose Maintain primary and secondary sex characteristics Promote sexual behavior and sex drive Promote spermatogenesis

Sperm Structure Acrosome Middle Piece Flagellum Digests egg protective barrier to allow nucleus to enter egg Middle Piece Mitochondria Flagellum Microtubules Controlled by centrioles

Female Reproductive Organs

Female Reproductive Organs Ovary Produce oocytes Meiosis I Produces hormones (estrogen and progesterone) Oviduct (fallopian tube) Transmits oocyte to uterus Site of fertilization Meiosis II Uterus Zygote implantation Placental development

Ovary and Oogenesis Meiosis I Meiosis II Inside ovary Primary oocyte (2n)  Secondary oocyte (1n) Meiosis II Inside oviduct after fertilization Secondary oocyte (1n)  Ovum (1n) Only one egg forms, other products of meiosis form polar bodies

Ovary and Oviduct

Ovary and Oogenesis

Female Reproductive Cycle Cyclic pattern (average 28 days) Menstrual and ovarian cycles Controlled by hormones Gonadotropin LH – luteinizing hormone FSH – follicle-stimulating hormone Ovarian hormones Estrogen Progesterone

Menstrual Cycle Three phases Menstrual flow phase (few days) Endometrial surface lost Proliferative phase (1-2 weeks) Endometrium regenerates Secretory phase (2 weeks) Endometrium thickens Glands develop and secreted glycogen No embryo implantation

Ovarian Cycle Two phases Follicular phase Luteal phase Primary follicle grows into a mature follicle (Graafian follicle) Ovulation occurs at the end of this phase Luteal phase Follicle cells become endocrine tissue and secrete hormones

Menstrual and ovarian cycles Menstrual and ovarian cycles run in parallel

Ovulation, Fertilization and Implantation

Fertilization Acrosome discharges enzymes to digest zona pellucida Once single sperm enters egg Egg releases enzymes that harden zona pellucida preventing other sperm from entering Sperm nucleus enters egg and fuses with egg nucleus

Placenta