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Animal Reproduction Terms

Get down with the lingo


A little sac at the head of a sperm. It is filled with enzymes that help the sperm get into an egg, like its own personal safe-cracking kit.


Different flavors of a gene, like brown eyes or blue eyes.


Special embryonic membrane in amniotic egg. Important for gas exchange.


Special embryonic membrane in an amniotic egg that directly surrounds the embryo/fetus. Filled with amniotic fluid. Makes the womb like a big water balloon.


Birds, reptiles, and mammals. Their eggs require special membranes because they develop on land.


Fish and amphibians. Their eggs develop in the water with only a simple embryonic membrane.

Asexual Reproduction

One parent required to reproduce. Nothing sexy about it.

Biological Imperative

The driving force to reproduce. It is almost like every animal is under a witch's spell to make more animals.

Blocks To Polyspermy

Things that happen to prevent an egg from being fertilized by more than one sperm. The egg doesn't have a bouncer at the door, so it uses other methods to get rid of extra sperm.

Blastocyst (or Blastula)

Stage of embryo development where cells form a hollow ball. Almost like somebody blasted out the middle.


Type of asexual reproduction where new animals grow like a blob on a parent and then split off


Special embryonic membrane in amniotes. Surrounds amniotic sac, allantois, and yolk sac. Lies just beneath the egg shell.


Long segment of condensed DNA consisting of many genes


An opening used for both reproduction and waste removal. Found in birds, reptiles, amphibians, and monotremes. You never know what is going to come out of this hole.


The act of physically bringing together the sex organs (for example, penis, cloaca, or vagina) for gamete release. The cops can't stop these gametes from getting together.


Same as copulation.


Finding and wooing a mate.

Courtship Ritual

Special behavior to communicate interest to a potential mate. Special dance moves, tail waggles, sniffing urine, etc.


A cell with two versions of every chromosome. This usually means one from the mother and one from the father.


One of the germ layers formed in gastrulation. It will form outer things like skin, hair, and teeth. It also forms the nervous system.


One of the germ layers formed in gastrulation. It will form most of the organs.


The female gamete, also called an oocyte. It can also mean the full structure that the oviparous embryo develops in, like a hard bird or reptile egg.

Egg Tooth

A tiny nub of hard deposit usually found on a baby bird's beak. It is used to break out of the egg. It usually falls off after hatching.


The act of a male releasing his sperm.

Estrous Cycle

The hormone cycle that controls a female's gamete production. Some mammals have a menstrual cycle instead.

External Fertilization

Union of sperm and egg that occurs outside the body in the environment. Some fish could probably sell tickets to this event.


Union of sperm and egg. That glorious moment when the gametes first meet.


Type of asexual reproduction where the animal splits in half (or sometimes more parts).


The whip-like tail that a sperm has. This powerful engine propels the sperm over huge distances.


Located in the ovary. Each follicle contains a single primary oocyte.


The happy haploid cells produced for sexual reproduction. Sperm and Eggs.


A stage of embryo development where the blastocyst differentiates and the cells are not identical anymore.


The process of differentiation where cells change into three different types of germ layers: ectoderm, endoderm, mesoderm. Each layer will develop into different types of tissue (and we don't mean Kleenex or Puffs).


Section of DNA that codes for a particular protein. For example, a gene for eye pigment determines your eye color. In reality, eye color is controlled by more than one gene, but let's keep it simple.


The collection of all your genes. It is a priceless one of a kind collection, unless you have an identical twin.

Germ Cells

The pre-gamete cells. Before they were sperm and eggs they were spermatogonia and oogonia.

Germ Layers

The first cells in an embryo that have a destiny. The three layers: ectoderm, endoderm, and mesoderm each have a different future.


A cell with only one version of every chromosome. Gametes are haploid.


A group of females controlled by one male, who has exclusive mating rights among those females.


An animal that can make both the male and female gametes. A Jack/Jill of all trades.

Internal Fertilization

Union of the sperm and eggs that takes place inside the mother. How hospitable.

Intersexual Selection

Mate selection where males and females are involved in selection. Usually one sex is choosy, and the other sex shows off.

Intrasexual Selection

Mate selection where males compete with males (or females compete with females). The other sex is usually just a super awesome amazing prize.


When an animal can reproduce more than once in its lifetime. They are doing "it" a lot.


The process of giving birth in viviparous animals like mammals.

Law Of Independent Assortment

Says that during meiosis each chromosome gets sorted into the 4 haploid gametes independently of the other chromosomes. So, a single gamete could have the maternal OR paternal version of chromosome 1 and the maternal OR paternal version of chromosome 2. The manager of giving out versions of chromosome 1 does not consult the manager of chromosome 2.

Law Of Independent Segregation

Says that each gamete only gets one version of each chromosome, either the maternal or the paternal version. This is obvious if you remember that gametes are haploid (and remember what haploid is).

Leydig Cells

Cells in the testes which secrete hormones during sperm production. Ooh ley ley.


A special type of mammal that delivers undeveloped young and then carries them in a pouch for further development. Kangaroos and Koala bears are marsupials.


A partner for sexual reproduction.


The process of sharing gametes in sexual reproduction. The conversation probably goes like this: "So, I'll provide the 30 million sperm, and you provide the one egg."


When children eat their (hopefully delicious and nutritious) mother. This has been well-studied in spiders.


The process of making 1 diploid cell into 4 haploid gametes. A genome replication followed by two splits.

Menstrual Cycle

The cycle of hormones which controls the build-up of the uterine lining. If an egg is not implanted, the endometrium is too sad to continue. It is then excreted from the body.


One of the germ layers. These cells will turn into muscle, blood vessels, and connective tissue.


Only having one mate. The old ball and chain could be around for one mating season or for their entire life.


Special type of mammals that lay eggs, like the platypus.


Stage of embryo development where the solid ball of cells look like a raspberry. This is right before they become a hollow blastocyst.


The female gamete. Also called an egg.


The process of producing the female gametes.


The female organ where oogenesis takes place.


An animal that develops in an egg (and gets nutrition only from the egg), but the egg is inside one of the parents and not in the environment.


An animal that develops in an egg that is out in the environment. Birds, reptiles, most fish, amphibians, and monotremes are oviparous.


When a female shoots an egg out of her ovary.


A virgin birth where the reproduction occurs even though the female egg has not been fertilized.


The process of giving birth. We bet many moms wish they just had an ejector seat button.


The male accessory sex organ used to deposit sperm inside a female for internal fertilization.


Chemicals that are released by some animals, often as a part of a courtship ritual. Mmm, smells like someone is available.


The connection between mother and fetus in mammals through which the fetus gets nutrition and gas and waste exchange.

Polar Body

The smaller cell formed in both the meiotic divisions of oogenesis. Only 1 of the 4 haploid cells created will become an oocyte. The others are polar bodies and will deteriorate.


Having more than one mate.

Primary Oocyte

The oocyte in arrest from birth until puberty. It will eventually undergo the first division of meiosis. Are they lazy or just very patient?

Primitive Streak

A section of cells formed early in gastrulation which makes the egg asymmetrical and provides the first bit or organization during gastrulation.


The process during meiosis where of bits of maternal and paternal chromosomes swap chunks of DNA.


A type of asexual reproduction where an animal can re-grow after part of it is removed. Perhaps vampires heal in a similar way.

Secondary Oocyte

The large cell after the first meiotic division of oogenesis that can be fertilized.


When an animal only reproduces one time in its life. Big-bang reproduction.

Seminiferous Tubules

The part of the testes where spermatogenesis party takes place.

Sexual Dimorphism

A difference between males and females. Size, color, strength, etc.

Sexual Reproduction

Reproduction requiring the union of sperm and egg.


Process of fish and amphibians releasing their gametes into the water for external fertilization. Have you ever seen a fish yawning while spawning?


The pre-sperm germ cells. They will become sperm at the end of spermatogenesis.

Spermatozoa (Sperm)

The male gamete.


The process of making sperm. There is a blue ribbon recipe in the Testicular Cookbook.

Testicles (Testes)

The male sex organ where sperm are produced.

Umbilical Cord

The cord that plugs the fetus into the placenta. Have you ever heard of cutting the cord? Yep, this is the one.


A female orifice only used for reproduction.


When animals give live birth. Mammals are viviparous.


A source of nutrition inside an egg. The yellow part inside a chicken egg is the yolk.


A fertilized egg.

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