Animal Reproduction Reproduction Sexual Reproduction Today, will tie many concepts together & build upon them in reproduction. We will cover: Reproduction Sexual Reproduction The Human Reproductive System

Reproduction The purpose of reproduction -to create new life (offspring) to pass DNA from P to F1. From the simplest bacteria to humans, is how living things create their offspring. How the DNA from P is passed to the F1. Does anyone have a dead parent or grand? If so, a part is still alive. Their genes, their DNA is alive within their descendents.

How does this whiptail lizard reproduce (it’s found in the American SW)? Other lizards.

Asexual Reproduction Some animals can reproduce asexually, producing offspring genetically identical to their parent (clones). Disadvantage -no genetic diversity is produced. Advantage –if the genotype is well adapted to the environment, this keeps the genotype.

Asexual Reproduction budding (yeast, some plants) regeneration, Methods of asexual reproduction: budding (yeast, some plants) regeneration, and parthenogenesis. (whiptail lizards)

Sexual Reproduction Sexual reproduction consists of: gametogenesis (gamete formation), mating, and fertilization. Gametogenesis and fertilization are similar in all animals. Mating has a great variety of anatomical, physiological, and behavioral adaptations.

Sexual Reproduction Advantage -genetic diversity is created by: recombination of genes during gametogenesis (crossing over) independent assortment of chromosomes. mating and fertilization in that two genomes are used.

Sexual Reproduction Disadvantages: If the genotype is well adapted to the environment, it is broken by sexual reproduction. It may be hard to find a mate. Only half your genome is passed to the offspring (asexual passes all of it).

Sexual Reproduction Gametogenesis occurs in testes and ovaries. In spermatogenesis and oogenesis, the primary germ cells proliferate mitotically, undergo meiosis, and mature into gametes. Review next two Figures

figure 42-04a.jpg Figure 42.4 – Part 1 Spermatogenesis

figure 42-04b.jpg Figure 42.4 – Part 2 Oogenesis

Sexual Reproduction Spermatogonia continue to proliferate by mitosis throughout the male’s lifespan. Each primary spermatocyte can produce four haploid sperm through two divisions of meiosis. Millions of sperm produced daily. Review Spermatogenesis.

Sexual Reproduction Primary oocytes immediately enter prophase of the first meiotic division, and in many species (humans), their development is arrested at this point. Each oogonium produces only one egg through meiosis. Review Oogenesis.

Overview Testes Sperm produced 300 million released Ovaries Male Testes Sperm produced 300 million released Female Ovaries One egg produced About every 28 days Oviduct Sperm encounter egg Fertilization

Sexual Reproduction sequential or simultaneous Hermaphroditic species have both male and female reproductive systems in the same individual. Hermaphrodites may be: sequential switch between male & female, some fish or simultaneous male & female at the same time earthworms.

Fertilization can occur externally: common in aquatic species. protects gametes from desiccation and heat. mating behaviors assure sperm and egg unite.

Fertilization can occur: internally Necessary in many terrestrial species. Terrestrial species have to keep the gametes and developing egg from drying out, so they to use internal fertilization usually involving copulation.

Sexual Reproduction Copulation brings the sperm and egg into close proximity. The shelled egg -an important adaptation to the terrestrial environment (desiccation). Yet, the egg must be fertilized before shell formation. All mammals except monotremes do not produce shelled eggs, retain the embryo internally.

Mammalian and Human Reproduction Copulation -males produce and deliver semen into the female reproductive tract. Semen consists of sperm suspended in a fluid that nourishes them and facilitates fertilization.

figure 42-08.jpg Figure 42.8 Figure 42.8

Spermatogenesis Primary spermatocytes Mitosis produces constant supply Tubules in testes Primary spermatocytes Mitosis produces constant supply Secondary spermatocytes After first stage of meiosis Two haploid cells Sperm After second stage of meiosis Four haploid cells Millions produced daily

figure 42-09b.jpg Figure 42.9 – Part 2 Figure 42.9 – Part 2

Oogenesis Ovaries Primary oocytes—by mitosis Prior to birth Primary oocytes—by mitosis Begin first meiotic division After puberty (about one/month) Completion of first meiotic division Secondary oocyte and polar body Secondary meiotic division begins Released into oviduct during ovulation Completes meiotic division after fertilization by sperm

The Human Reproductive System Eggs mature in the female’s ovaries are released into the oviducts, which deliver the eggs to the uterus. Sperm deposited in the vagina move through the cervix into the uterus, some continuing up through the oviducts. Egg secondary meiotic division completed after fertilization by sperm

figure 42-11.jpg Figure 42.11 Figure 42.11

figure 42-12.jpg Figure 42.12 Figure 42.12

Fertilization Ovum Follicle cells and coating Much larger than sperm Millions released Only hundreds reach ovum Acrosome Front tip of sperm—contains enzymes Digest outer covering Fertilization Two nuclei fuse

Mate Selection Important for successful reproduction Providing parental care and sustenance

Mate Selection Important for successful reproduction Ensures quality of genes Investment of female vs. male in reproduction Many animals—females choose more carefully, invest a lot more than male Some animals mate for life

Human Sexual Behavior Human sexual responses consist of: excitement, plateau, orgasm, and resolution. Males have a refractory period during which renewed excitement is not possible.

Human Sexual Behavior Methods to prevent pregnancy include abstention from copulation or use of technologies that decrease the probability of fertilization. Review Table 42.1

table 42-01.jpg Table 42.1 Table 42.1