Animal ReproductionBy: Madison Allen

Asexual vs. Sexual Reproduction

In sexual reproduction, the fusion of haploid gametes forms a diploid cell, the zygote. The animal that develops from a zygote can in turn give rise to gametes by meiosis. The female gamete, the egg, is a large, nonmotile cell. The male gamete, the sperm, is generally a much smaller, motile cell.

Asexual reproduction is the generation of new individuals without the fusion of egg and sperm. In most asexual animals, reproduction relies entirely on mitotic cell division.

Asexual Reproduction

Many invertebrates can reproduce asexually by fission, the separation of a parent organism into two individuals of approximately equal size.

Also common among invertebrates is budding, in which new individuals arise from outgrowths of existing ones. ◦Ex. In certain species of coral and hydra, new

individuals grow out from the parents body.Parthenogenesis is a form of asexual

reproduction in which an egg develops without being fertilized.

Asexual Reproduction

Sexual Reproduction

The vast majority of eukaryotic species reproduce sexually.

Most animals exhibit cycles in reproductive activity, often related to changing seasons. In this way, animals conserve resources, reproducing only when sufficient energy sources are available and when environmental conditions favor the survival of offspring. ◦ For example, ewes (female sheep) have a reproductive

cycle lasting 15-17 days. Ovulation is the release of mature eggs and occurs

at the midpoint of each cycle. Reproductive cycles are controlled by hormones,

which in turn are regulated by environmental cues. ◦ Common environmental cues are changes in day length,

seasonal temperature, rainfall, and lunar cycles.

Sexual Reproduction

Sexual Reproduction Continued

Hermaphrodism is when each individual has both male and female reproductive systems. Because each hermaphrodite produces as both male and female, any two individuals can mate. ◦This is present in stationary animals, such as

barnacles, burrowing animals, such as clams, and some parasites, such as tapeworms.

External vs. Internal Fertilization

Fertilization is the union of sperm and egg, which can be either external or internal.

External fertilization – the female releases eggs into the environment, where the male fertilizes them

Internal fertilization – sperm are deposited in or near the female reproductive tract, and fertilization occurs within the tract

External

Internal

Reproductive Organs

In many insect species, the female reproductive system includes a spermatheca, a sac in which sperm may be stored for extended periods, a year or more in some species.

In many nonmammalian vertebrates, the digestive, excretory, and reproductive systems have a common opening to the outside, the cloaca.

Female Reproductive Organs

Ovaries – the female gonads are a pair of ovaries that border the uterus and are held in place in the abdominal cavity by ligaments (ovaries produce eggs and reproductive hormones)

Uterus – where eggs are fertilized and development of the young occurs

Female Reproductive Organs

Male Reproductive Organs

Testes – consists of many highly coiled tubes surrounded by several layers of connective tissue, this is where the sperm is formed

Male Reproductive Organs

Spermatogenesis

Spermatogenesis – the formation and development of sperm, is continuous and prolific in adult males

Oogenesis

Oogenesis – the development of mature eggs, is a prolonged process in the human female

Conception and Birth

Human gestation is divided into three trimesters of about three months each. ◦First, Second, and Third Trimester

Placenta – a structure in the pregnant uterus for nourishing a viviparous fetus with mother’s blood supply; formed from the uterine lining and embryonic membranes

Labor – the process by which childbirth occurs; a series of strong, rhythmic uterine contractions

Of course, protection is always an option ;)