Animal Reproduction and Development

By: Xander Posner

Methods of asexual reproduction. Pheromones in mating attraction. Different sexual reproductive methods. Components of reproductive system. Methods of fertilization. Process of Cleavage Cell stages, gastrulation, etc. Extraembryonic membranes

Overview

Asexual (meaning without sex) reproduction - Creation of new individuals from which all of the gametes come from one parent, without meeting of gametes. Does NOT increase genetic diversity.

Sexual Reproduction – Creation of offspring by the fusion of haploid gametes to form a zygote (fertilized egg) which is diploid. Increases genetic diversity

Sperm – Small, motile, male sex cell. Ovum (Egg) – Larger, not motile, female sex cell

Key Terms

There are four types.

Fission Budding Fragmentation &

Regeneration Parthenogenesis

Types of Asexual Reproduction

Fission in Amoeba

Parthenogenesis is a process in which an egg develops without fertilization.

Occurs in crustaceans, bees, wasps, ants, reptiles and others.

The switching from asexual to sexual reproduction is usually induced by season or other environmental stress.

Plays large role in ant and bee colonies where fertile females become queens and the sterile individuals in which meiosis never occurred become worker ants or bees.

http://www.hippocampus.org/homework-help/Biology/The%20Reproduction%20of%20Cells_Sexual%20Life%20Cycle%20&%20Meiosis-%20Summary.html

Parthenogenesis

Chemical signals released by animals that play large role in mate attraction

Released into air, can be sensed by animals such as bees over a Km away.

Occur in minute amounts, like hormones.

Pheromones

Reproductive Systems

Vagina

Uterus

Cervix

OvariesOviduct

Uterine wall

Endometrium

Follicles

Corpus luteum

Seminal vesicle

(Rectum)

Vas deferens

Ejaculatory duct

Prostate gland

Bulbourethral gland

(Urinarybladder)

(Pubic bone)

Erectiletissue of

penis

Urethra

Glans penis

Prepuce

Vas deferensEpididymis

Testis

Scrotum

Menstrual cycle occurs due to changes in the uterus. Also called uterine cycle.

Caused by cyclic events in the ovaries, or by the ovarian cycle.

Female Cycles

Figure 46.13

Sexual reproduction involves meiosis (to create gametes)

But how do these gametes come about you may ask?

Oogenesis – Creation of female ova. Figure 46.11

Spermatogenesis – Creation of male sperm cells. Figure 46.12

Creation of Gametes

Begins with fertilization – meeting of gametes. Once egg is fertilized, activation of the egg occurs and

rapid changes result. Some changes are: Increase in cytoplasmic Calcium (Ca2+), which hardens

the egg lining, preventing additional sperm from entering.

This increase in Ca2+ also increases rates of cellular respiration and protein synthesis by the egg cell.

The sperm nucleus within the egg cell begins to swell. After about 20 minutes, the nucleus of the sperm and egg fuse, forming the diploid zygote and BAM, the beginning of new life.

Development

Fertilization Sea Urchins Gametes meet externally when

they are released into surrounding water.

Acrosomal reaction, when urchin sperm release hydrolytic enzymes to break down the jelly coat of an egg cell and enter it.

Once a sperm penetrates, the gametes plasma membranes fuse, rapidly preventing polyspermy.

Cortial Reaction – Sperm binding induces signal transduction pathway that induces a long-term prevention of polyspermy.

Mammals Gametes meet internally after

sperm swim up the fallopian tubes.

Sperm binds to membrane of egg.

Virtually same acrosomal reaction occurs. Once sperm breaks down the outer coating of the egg cell, membrane proteins of the sperm bind to receptors in the egg and the plasma membranes fuse.

Sperm nucleus and other components enter egg cell.

Enzymes are released during the cortical reaction that block polyspermy.

After fertilization, rapid cell divisions occur. This process is called cleavage. Cells undergo the S (DNA synthesis) and M (Mitosis) stages

but skip the G phases so virtually no protein synthesis occurs. Each new cell has its own nucleus. Cell divides into about 128 cells until the blastula is created. Blastula is a hollow ball of cells.

Cleavage… The Cell Type

Gastrulation is the infolding of the blastula forming 3 cell “germ” layers and the cell’s primitive gut. Process of infolding is called invagination

Allows new interactions of cells 3 Layers created are: Ectoderm (Outer layer) Endoderm (lines the embryonic digestive tract) Mesoderm (Which partly fills space between the ectoderm

and endoderm)

Gastrulation

VIDEO TIME

Membranes associated with animals that aid in their embryonic development.

Adaptations that allow live or shelled egg birth on land. Found in reptiles (and birds), and mammals. 4 extraembryonic membranes of birds and reptiles are: The amnion (Prevents dehydration and cushions) The allantois (Disposal sac for metabolic waste, and as

respiratory organ) The Chorion (exchange gases between embryo and

surrounding air) The Yolk sac (Stockpile of nutrients for embryo) All arise from 3 germ layers.

Extraembryonic Membranes

Blastocyst is hollow ball of cells; mammalian version of blastula. Cluster of cells within blastocyst called inner mass cells will contribute most

of the extraembryonic membranes. Trophoblast is part of the blastocyst that secretes hydrolytic enzymes that

allow the blastocyst to enter the lining of the uterus. Gastrulation occurs once the blastocyst is implanted in the uterine lining.

The 3 germ layers formed by the end of gastrulation form the extraembryonic membranes. The membranes created are:

The chorion (gas exchange) The amnion (encloses embryo in protective fluid, this fluid exits the vagina

when a woman’s “water breaks,” before childbirth) The yolk sac (encloses fluid filled cavity, site of early formation of blood

cells.) The allantois (incorporated into the umbilical cord, forms blood vessels that

transport oxygen and nutrients from the placenta to the embryo and also function in removal of waste.

By the end of the first trimester of pregnancy, rudiments of all the major organs have developed from the 3 germ layers.

Mammalian Development

THE END