Cell Differentiation All cells in an embryo descend from the same zygote and have the same genes ________________________: Certain groups of genes are activated in some cells but not in others Genes are not lost, just inactivated Different cell lineages become specialized in composition, structure, and function Body has ______ differentiated cell types

Cell Communication in Development __________________: signaling molecules produced by master genes – Secreted by cells – Effect on target cell is proportional to its concentration Embryonic induction occurs when embryonic cells produce signals that alter the behavior of neighboring cells Example: cells at dorsal lip

Morphogenesis Orderly changes result in specialized tissues and early organs Cells ____________ Whole sheets of cells expand and fold Programmed cell death (_____________) sculpts body parts Cell migration

Morphogenesis: Neural tube formation neural groove neural tube ectoderm at gastrula stage ectoderm

7. Organ Formation Newly forming cells increasing specialized in structure and function Tissues and organs mature in size, shape and formation

__________ Development fate of embryonic cell lineages changes upon exposure to gene products from adjacent tissues Cells behave as if they have positional memory Demonstrated experimentally by transplanting embryonic cells

Cell Memory: _____________________ Transplant organized formation of second set of structures

Cell Memory: Chick Wing Development mesoderm of developing forelimb in a chick embryo wing AER removed leg forms graft of meso- derm from leg A. Remove a wing bud’s AER, and wing development stops. B. Graft a bit of leg mesoderm beneath the AER and part of a leg—even some toes—develops.

Morphogens Substance governing the pattern of tissue development Spreads from a localized source and forms a concentration gradient across a developing tissue Gradient helps a cell chemically assess its position in the embryo and how it should differentiate Influences which genes are turned on or off

________ ___________ Process through which certain body parts form in a specific place Starts with ________________________ (where cells are located relative to the original maternal cytoplasm) Classes of master genes activated in sequence Interactions among master genes are guided by regulatory proteins Gene products are spatially organized in the embryo

Similar Master Genes Diverse animals use similar or the same master genes to govern development May help explain why ____________________________________ The relatively small number of master genes constrains variation

The Reproductive System Gonads – _________________________ – Testes in males – Ovaries in females Gonads produce ____________ (sex cells) and secrete _____________ – Sperm – male gametes – Ova (eggs) – female gametes

Male Reproductive System Testes Duct system – Epididymis – Vas deferens – Urethra Figure 16.2b

Male Reproductive System Accessory organs – Seminal vesicle – Prostate gland – Bulbourethral gland External genitalia – Penis – Scrotum

Testes Males have 2 gonads called testes __________________ Few degrees cooler than body temperature for sperm development Seminiferous tubules – Tightly coiled structures – Function as sperm-forming factories Produce _____________ Figure 16.1

Epididymis Comma-shaped, tightly coiled tube Sperm travels from testes to epididymis Function: to mature and store sperm cells – At least ____________________ Expels sperm with the contraction of muscles in the epididymis walls to the vas deferens

Vas Deferens Carries sperm from epididymis to the ejaculatory duct _________________ – cutting of the vas deferens at the level of the testes to prevent transportation of sperm

Urethra Extends from the base of the urinary bladder to the tip of the penis Carries ______________________ Sperm enters from the ejaculatory duct

Semen = _________ + ________ Secretions from epididymis aid sperm maturation Other secretions come from: – Seminal vesicle – Prostate gland – Bulbourethral gland

Seminal Vesicles Located at the base of the bladder Produces a thick, yellowish secretion (60% of semen) – Fructose (sugar), Why? – Vitamin C – Prostaglandins – Other substances that nourish and activate sperm

Prostate Gland Encircles the upper part of the urethra Secretes a milky fluid – Helps to activate sperm – Enters the urethra through several small ducts Functions to ___________________________

Bulbourethral Glands Pea-sized gland Produces a thick, clear mucus – Cleanses the urethra of acidic urine – Lubricates urethra so sperm can get through

Semen Mixture of sperm and accessory gland secretions Advantages of accessory gland secretions – Fructose provides energy for sperm cells – Alkalinity of semen helps neutralize the acidic environment of vagina – Semen inhibits bacterial multiplication – Elements of semen enhance sperm motility

External Genitalia Scrotum – Divided sac of skin outside the abdomen – Maintains testes at 3°C lower than normal body temperature to protect sperm viability Penis – Delivers sperm into the female reproductive tract – Internally, three areas of spongy erectile tissue around the urethra

Sperm Formation: Seminiferous Tubules

Spermatogenesis Production of sperm cells Begins at puberty and continues throughout life In the seminiferous tubules (inside testes) Spermatogonium (2n) divides by mitosis to form primary spermatocyte (2n) Meiosis produces haploid spermatids Spermatids mature to become sperm Spermatogenesis takes 64 to 72 days

Anatomy of Mature Sperm The only human flagellated cell DNA is found in the head Little cytoplasm hour lifespan (up to 5 days) Figure 16.5b

Testosterone Production Produced in Testes by ______________ Functions of testosterone – Stimulates reproductive organ development – Underlies sex drive – Helps develop and maintain sexual behavior – Causes _____________________________ Deepening of voice Increased hair growth Enlargement of skeletal muscles Thickening of bones

Regulation of Male Androgens (Sex Hormones) Figure 16.6

Hormone Controls Gonadotropin-releasing hormone (_______) from the hypothalamus stimulates the secretion of LH and FSH Luteinizing hormone (____) is released by the anterior pituitary and stimulates testosterone produced Follicle-stimulating hormone (_____) stimulates the production of sperm beginning at ____________