Animal Reproduction

Asexual reproduction

Based on mitosis and results in offspring that are genetically identical to one another and to their parent

Sexual reproduction

based on meiosis and fusion of gametes

Three mechanisms of asexual reproduction

1. Budding- the offspring forms in or on the parent (hydra)

2. Fission- an individual splits into two organisms (anemones)

3. Parthenogenesis- the female produces an offspring without fertilization from a male (lizards)

Gametogenesis

the process in which cells undergo meiosis to form gametes

Spermatogenesis

formation of sperm

Oogenesis

the formation of eggs

In the majority of animals, gametogenesis occurs where?

the sex organ called the gonad

What are male and female gonads called?

testes, ovaries

What happens in the male gonad

diploid cells called spermatogonia divide by mitosis to generate the cells that undergo meiosis

In humans, the spermatogonia divide by mitosis to produce what?

primary spermatocytes, which undergo meiosis I and produce two secondary spermatocytes

What is the result of the spermatogenesis in Mammals?

four haploid cells called spermatids, each of which matures into a sperm

In the female gonad diploid cells called ___ divide by mitosis to form ___

oogonia, primary oocytes

When oogonia and primary oocytes undergo meiosis ____

only one of the four haploid products (ovum) matures into the egg (other cells that do not mature into eggs are called polar bodies)

What are the four components of the mammalian sperm?

1. The head- contains the nucleus and an enzyme acrosome (penetrates the egg)

2. The neck- contains one centriole, which will combine with the centriole contributed by the egg

3. A midpiece- contains mitochondria, which supply the ATP that powers the sperm to swim to the egg

4. A tail- with flagellum for swimming

The structure of the Mammalian egg

1. Yolk- nutrient source loaded with protein and fats

2. Vitelline envelope- outside the cell membrane (zona pellucida)

Animals that rely on external fertilization …

-live in aquatic environments

-produce large number of gametes

-gametogenesis occurs in response to environmental cues

-gametes are released based on specific cures from the same species

pheromones

chemical messengers involved in the coordination of the release of gametes

What are the two ways internal fertilization can occur

1. Copulation - male deposits sperm directly into the female reproductive tract with the aid of a copulatory organ called the penis

2. males may package them sperm into a spermatophore, which is then placed into the female’s reproductive tract

Femmes fatales

arthropod females cannibalize the male before the copulation is completed, increasing the number of fertilized eggs

Giant sperm

fruit flies produce sperm that are so large they prevent additional matings with other males

False penises

red-billed buffalo weaver has a false penis that becomes erect during copulation, stimulating the female’s reproductive tract

Infidelity

in birds, some nests include at least one offspring fathered by a male not mated to the resident female

Love darts

snails and slugs are hermaphroditic, they contain both male and female gonads. They fire love darts into the mating partner

Hypodermic insemination

hypodermic penises that function like a needle. Male force the organ through the female’s wall and deposit sperm (bed bugs)

In humans, the male reproductive system consists of…

the scrotum - holds the testes
penis - organ of copulation

Anatomy of Human Male reproductive organs (1)

spermatogenesis and sperm storage- sperm are produced in the testes and stored in the nearby epididymis

Anatomy of Human Male reproductive organs (2)

Production of additional fluids- fluids are formed in the seminal vesicles, prostate gland, and bulbourethral gland (added to the sperm before ejaculation)

Anatomy of Human Male reproductive organs (3)

Transport and delivery- the vas deferens are tubes that transport sperm from the epididymis to the ejaculatory duct. The semen then enters the urethra, a long tube that passes through the penis

Humans are viviparous vertebrates. What does that mean?

the female retains the embryo and provides the nourishment

What does the external anatomy of the human female reproductive system consist of?

-Labia minor & labia major - folds of skin that cover the vaginal openings

-The clitoris - sensitive organ that develops from the same embryonic cells that form the penis

-The vagina - chamber where semen is deposited

Anatomy of Human Female reproductive organs (1)

Production and transport of eggs:
- eggs are produced in the paired ovaries
- during ovulation, an egg is expelled from the ovary and enters the oviduct
- fertilized eggs are then transported to the uterus

Anatomy of Human Female reproductive organs (2)

Development of offspring:
-embryo develops in the uterus
-fetus passes through the cervix and into the vagina

Male & Female sex hormones

testosterone, estradiol, belong to hormones called estrogens

Where are estrogens produced

in the ovaries by cells that form the follicle

3 roles of sex hormones

1. development of the reproductive tract in embryos

2. maturation of the reproductive tract during the transition from childhood to adulthood

3. regulation of spermatogenesis and oogenesis in adults

Female mammals that do not mensturate

estrous cycle

First phase of the menstural cycle

The follicular phase- 14 days the follicle matures and ovulation occurs

Second phase of the menstrual cycle

luteal phase- corpus luteum forms the ruptured follicle

Humans are an example of eutherian reproduction because..

-many events occur before and during pregnancy
-an egg released from the ovary is viable for less than 24 hours
-sperm remain capable of fertilizing an egg for up to 5 days

By the time the embryo reaches the uterus, it undergoes _____

Implantation in the wall of the uterus

The first trimester

gestation is divided into 3 trimesters
three embryonic tissues form
8 weeks the tissues have become different organs and systems (fetus)

What hormone does the embryo secrete?

human chorionic gonadotropin

What happens when hCG is present

the corpus luteum does not disintegrate, the ovary continues to secrete progesterone, and the menstrual cycle stops