ch-36-PPTaccessible

Chapter 36: Reproduction and Development

Introduction

• Textbook: Campbell Biology in Focus, Fourth Edition

• Authors: Kathleen Fitzpatrick, Simon Fraser University; Nicole Tunbridge, Kwantlen Polytechnic University

• Copyright: 2016, 2020, 2025 Pearson Education, Inc.

Modes of Reproduction

Asexual vs. Sexual Reproduction

• Sexual Reproduction: Fusion of male gamete (sperm) and female gamete (egg) to form a zygote.

• Asexual Reproduction: Offspring are produced without the fusion of egg and sperm.

Mechanisms of Asexual Reproduction

Common Methods (Invertebrates)

• Budding: New individuals arise from outgrowths of existing ones.

• Fission: Parent organism separates into two roughly equal-sized individuals.

Additional Mechanisms

• Fragmentation: Breaking of the body into pieces that develop into adults; requires regeneration.

• Parthenogenesis: Development of a new individual from an unfertilized egg; occurs in some vertebrates under low population conditions.

Sexual Reproduction: Costs and Benefits

• Twofold Cost of Sexual Reproduction: Sexual females produce half as many daughters compared to asexual females.

• Sexual reproduction increases genetic variation, which may enhance survival in changing environments.

• Asexual reproduction may thrive in stable, favorable environments.

Reproductive Cycles

Overview

• Many animals exhibit reproductive cycles related to seasonal changes, influenced by hormones and environmental cues.

• Climate change can impact reproductive success by altering these cues.

Whiptail Lizards Example

• Breeding pairs where females alternate roles, mimic male behavior, and undergo ovulation without males.

Variation in Sexual Reproduction

Hermaphroditism

• Individuals possess both male and female reproductive systems, allowing any two hermaphrodites to mate.

Sex Reversal

• Examples include bluehead wrasse where largest female transforms into a male if the male dies.

Fertilization Types

External Fertilization

• Occurs when eggs are shed and fertilized in the environment; requires moisture to prevent gamete desiccation.

Internal Fertilization

• Sperm deposited in or near the female reproductive tract; more efficient in dry environments.

Ensuring Offspring Survival

• Internal fertilization usually results in fewer gametes but a higher survival rate for zygotes.

• Protection mechanisms for embryos include egg shells or retaining embryos within the female.

Reproductive Organs and Gametes

• Gonads produce gametes; additional structures assist in transport and protection of gametes.

Male Reproductive Anatomy

External Structures

• Scrotum and penis.

Internal Structures

• Gonads (testes) produce sperm and hormones, accessory glands, and ducts for sperm transport.

Female Reproductive Anatomy

External Structures

• Clitoris and labia.

Internal Structures

• Ovaries, oviducts, uterus, and vagina.

Gametogenesis: Production of Gametes

Types

• Spermatogenesis: Continuous sperm production in males; each sperm takes about 7 weeks to develop.

• Oogenesis: Egg development; immature eggs can take years to mature; one mature egg is produced from meiosis.

Hormonal Control of Reproduction

Mammalian Reproductive Hormones

• Hormone regulation involves hypothalamus, anterior pituitary, and gonads.

Male Hormonal Regulation

• FSH and LH direct spermatogenesis; testosterone regulates GNRH, FSH, and LH productions through feedback mechanisms.

Female Hormonal Regulation

• Two reproductive cycles: ovarian cycle (egg release) and menstrual cycle (uterine preparation).

Human Sexual Response Phases

• Phases include excitement, plateau, orgasm, and resolution.

• Physiological changes involve muscle tension and blood flow in genital areas.

Embryonic Development Stages

Fertilization

• Involves egg activation and successful entry of sperm.

Cleavage and Gastrulation

• Cleavage: rapid cell division post-fertilization; blasts produced.

• Gastrulation: germ layers formed and digestive structures developed.

Organogenesis

• Development of organs from embryonic germ layers.

Gestation

• Average human pregnancy lasts around 38 weeks; organ formations during the first trimester.

Fetal Development and Birth

• Childbirth involves uterine contractions; milk production stimulated by infant suckling through hormonal responses.

Contraception

Overview

• Methods to prevent pregnancy include hormonal, barrier methods, and withdrawal techniques; effectiveness varies.

Infertility and IVF

• Infertility affects a significant percentage of males and females; in vitro fertilization offers treatment options.