Animal Reproduction

Animal Reproduction • HW 3 & midterm2 (Harry Potter Punnet square questions) • 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 • 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 in 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 till puberty. • Each oogonium produces only one egg in meiosis. Review Oogenesis.

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

Sexual Reproduction • 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 terrestrial species. • Terrestrial species have to keep the gametes and developing egg from drying out, so they to use internal fertilization usually involving copulation. • Copulation -males deliver semen into the female reproductive tract.

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 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 CourseContent

The foreskin or prepuceis absent after circumcision

Spermatogenesis • 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 • 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

Figure 42.13 – Part 1

Fertilization Ovum • Follicle cells and coating • Much larger than sperm 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, review Table 42.1

table 42-01.jpg Table 42.1 Table 42.1

Animal Reproduction