DAT Biology Chapter 12 Reproduction and Developmental Biology

Binary Fission

Done by unicellular organisms.

DNA is replicated, migrates to opposite ends of the cell.

Septum in middle form dividing wall and splits into two

Septum

Appears in middle of cell during binary fission and splits into two to create two separate cells.

Budding

Bud (outgrowth) forms on the organism.

DNA is replicated and deposited into bud, which buds off, yeast.

Ex. Hydra and Yeast

Regeneration or Fragmentation

Piece of organism breaks off.

Can regenerate broken pieces or sometimes a new organism can grow from a fragment.

Ex. Hydra and Planaria

Parthenogenesis

Unfertilized egg develops to a viable organism.

Usually can do sexual or asexual

Sexual when not ideal conditions

Haplodiploidy

Sex determination based on whether haploid or diploid

Honeybee’s Haplodiploidy

Unfertilized form haploid male

Fertilized form diploid female

Sexual Reproduction

Joining of two distinct gametes to create offspring.

Germ Cells

Produce gametes via meiosis

Only cells in body that undergo mitosis and meiosis

Spermatogonia

Male Germ Cells

Oogonia

Female Germ Cells

Spermatogonia Formation

Spermatogonia replicates by mitosis in seminiferous tubules of testicles

Some undergo completion of first and second meiotic division to form spermatids

Spermatozoa

Multiple mature sperm cells

Spermatogenesis Process

Undergo two meiotic divisions to become 4 spermatids and differentiate into sperm.


1. Seminiferous tubules of testes = site of spermatogenesis (sperm production) and contain


1. Sertoli Cells: activated by follicle stimulating hormone (FSH). Surround and nourish sperm. Produce inhibin (inhibits FSH - negative feedback
2. Spermatogenic Cells: Produce spermatozoa
2. Sperm transported via peristalsis to epididymis (duct around testes) for maturation and storage
3. Sperm moves through vas deferens (group of tubules) to ejaculatory duct (where vas deferens meets seminal vesicles) which propels sperm into sperm into urethra and leads to ejaculation out of penis as semen (sperm + accessory gland secretions)

Sperm Structure

Head

Midpiece

Tail

Head of Sperm

Contains nucleus

Contains acrosome

Acrosome

Contains digestive enzymes that help sperm penetrate egg for fertilization upon contact

Midpiece of Sperm

Contains lot of mitochondria

Provide energy to move through female reproductive system

Tail

Long flagellum that moves around

Propels sperm forward and gives mobility

What is the tail of the sperm made of?

Microtubules that are made by tubulins

Testes

Male reproductive gland

Contains seminiferous tubules that produce sperm

Contains sertoli cells and spermatogenic cells

Sertoli Cells

Surrounds and nourish developing sperm cells within testes

Activated by FSH

Secrete inhibin that inhibit FSH release making a negative feedback

Epididymis

Duct that sits around testes

Sit of sperm storage before ejaculation

Sperm continue to mature here

Vas deferens

Group of tubules that helps move sperm epididymis to ejaculatory ducts

Peristalsis

Contraction of smooth muscle

Help sperm move before they mature

Ejaculatory ducts

Where vas deferens meet seminal vesicles

Propel sperm to urethra, which leads to ejaculation

SEVEn UP

Seminiferous tubules, Epididymis, Vas deferens, Ejactulatory duct, Urethra, Penis

Semen

Combination of sperm and secretions from accessory glands

Seminal Vesicles

Secretes fructose, viscous mucus and prostaglandins

Provides sperm nutrients to produce ATP for motility

Cleans and lubricate urethra

Stimulate contraction of urethra

Viscous Mucus

Secreted by Seminal Vesicles

Cleans and lubricates the urethra

Protstaglandins

Secreted by seminal vesicles

Stimulates contraction of urethra

Help sperm move through urethra

Prostate Gland

Make semen more alkaline (basic) so sperm can survive acidity of female reproductive tract

Bulbourethral Glands

Secretes Viscous mucus (cleans and lubricates urethra)

Hormones in Males

Follicle Stimulaing Hormone

Luteinizing Hormone

Testosterone

Follicle Stimulating Hormone in Males

Stimulates sperm development in seminiferous tubules

Luteinizing Hormone in Males

Stimulates Leydig cells to produce testosterone

Testosterone

Mature sperm, give rise to male secondary sex characteristics

Ovary

Produces eggs which travel through oviduct to uterus

Oviduct

Fallopian tube

Uterus

Muscular, vascular organ.

Provides an ideal environment for fertilized egg to implant and develop.

3 Layers of Uterus

Perimetrium

Myometrium

Endometrium

Perimetrium

Outer layer of uterus

Myometrium

Middle layer of uterus

Smooth muscle

Endometrium

Inner epithelial layer of uterus

Lined by mucous membranes

Cervix

Narrow opening of uterus leading to vagina

Vagina

Opens to external environment

(where sperm enters and birth occurs)

Oogonia

Primordial egg cells

Replicated by mitosis

Start with huge amount and most undergo apoptosis

Small fraction remain

Primary Oocytes

Remaining oogonia differentiate to this

Begin meiosis 1 but arrest in prophase 1 until puberty

Puberty

Every month, one of eggs will be stimulated to go through ovulation.

Ovulation

Egg complete meiosis 1

Large secondary oocyte and polar body produced

Secondary Oocyte

Arrest in metaphase 2

Only complete meiosis 2 when fertilized

Oocyte

Nutrients for fetus

Majority of cytoplasm and mitochondria compared to sperm

Hormones in Females

Follicle Stimulating Hormone

Luteinizing Hormone

Estrogen and Progesterone

Follicle Stimulating Hormone in Females

Stimulates follicles in the ovary to develop.

Follicle produces progesterone and estrogen

Follicle

Stimulated by FSH and produce progesterone and estrogen

Luteinizing Hormone

Surge causes ovulation of egg and formation of corpus luteum

Corpus luteum

Produces progesterone and estrogen

From remnants of follicle after ovulation

Estrogen and Progesterone

Female sex hormones

Contribute to menstrual cycle and reproduction

Contribute to breast development

Inhibit hypothalamus and pituitary gland

Birth Control Pills

Release synthetic estrogen and progesterone

Inhibiting GnRH production during menstrual cycle through negative feedback and thus preventing menstrual cycle from causing ovulation

Menstrual Cycle

Follicular Phase

Ovulation

Luteal Phase

Implantation

Day 28 of menstrual cycle

Estrogen and progesterone drops

Hypothalamus and Pituitary start producing hormone again

GnRH

Produced by hypothalamus

Causes releasing of LH and FSH from anterior pituitary gland

Anterior pituitary gland

Release LH and FSH

Tropic Hormones

Released from one endocrine gland and stimulate another endocrine gland

Ovarian Follicles

Develop when FSH bind to ovaries

Graafian Follicle

One follicle that develop the most

Where egg to be ovulated will be released from

Produce estrogen

Endometrium and Estrogen

Thicken its tissue and become engorged with blood

Prepare uterus in case of fertilization

Spike in LH

Caused by increase in estrogen

Ovulation

Due to spike in LH

Release of egg from follicle

If no Implantation

FSH and LH lowers

Estrogen and Progesterone also drops

Endometrium can no longer be maintained

Causing menstruation

Implantation

Menstruation is prevented

Outer layer of placenta begins to secrete hCG

Corpus luteum supported by hCG and produce more progesterone and estrogen

Human Chorionic Gonadotropin

Maintains the corpus luteum after implantation

Positive Feedback Loop

Stimulates pathway to increase production

Lactation

Childbirth

Lactation

Infant suckling increases prolactin production which causes lactation (milk production) and further increases infant suckling.

Oxytocin releases milk

Prolactin

Stimulate lactation

Oxytocin

Releases the milk

Increase contractions in labor

Childbirth

Oxytocin induces contractions which push the baby out of womb.

Baby pushes against a nerve in cervix that signals hypothalamus and pituitary to release more oxytocin

Negative Feedback Loops

Inhibit pathway to decrease production

Hypothalamus releases GnRH causing pituiary to release FSH and LH which increase testosterone levels. High testosterone levels inhibit the hypothalamus from releasing GnRH, lowering FSH and LH and testosterone

Fertilization

Joining of haploid sperm and haploid egg to form diploid zygote

Egg Structure

Corona Radiata

Vitelline Layer

Plasma Membrane

Corona Radiata

Outermost Layer

Composed of follicular cells

Nourishes egg

Vitelline Layer

Made of glycoproteins

Surrounds plasma membrane of egg

Also called zona pellucida or jelly coat

Plasma Membrane of Egg

Underneath zona pellucida

ZP3

Protein that binds to sperm and stimulates the acrosome reaction

Fertilization Process

1. Capacitation
2. Acrosomal Reaction
3. Polyspermy Block
4. Completeion of Meiosis 2 for secondary oocyte
5. Zygote Formation

Capacitation

Final maturation step for sperm to prior to fertilization

As it sperm moves up female reproductive tract, secretion from uterine wall triggers capacitation

Destabilize sperm’s plasma membrane

Destabilize sperm’s plasma membrane

1. Prepares tip of sperm for acrosomal reaction
2. Increases permeability to calcium

Acrosomal Reaction

Recognition process between sperm and egg

Ensure same-species fertilization

Acrosomal Enzymes

Digest through zona pellucida

Sperm can then fuse with egg’s plasma membrane

Polyspermy

More than one sperm penetrate egg

Polyploidy

More than two copies of chromosomes

Caused by polyspermy

Polyspermy Block

Prevents polyploidy by inhibiting polyspermy (multiple sperms penetrating egg)

Fast Block

Slow Block

Fast Block

Occurs immediately after sperm fuse with egg

Sodium diffuse into egg and become depolarized

Depolarization repels additional sperm

Slow Block

Calcium ions released inside egg’s plasma membrane

Egg undergo cortical reaction

Cortical Reaction

Exocytosis of cortical granules

Form a fertilization envelop to prevent polyspermy

Slow Block

Cortical Granules

Changes zona pellucida in impenetrable envelope

Stimulate proteases

Proteases

Protein cutting enzymes

sever link between zona pellucida and plasma membrane

Completion of Meiosis 2 for secondary oocyte

During meiosis 2, egg is stopped in metaphase.

After penetration, meiosis in secondary oocyte continues creating a haploid oocyte and producing a second polar body

Monozygotic Twins

Identical Twins.

One fertilization to one zygote when then split

Dizygotic Twins

Fraternal Twins.

Two separate eggs fertilized by two separate sperms. Two zygotes with different genetic material