28.3 Reproduction
How do asexual and sexual reproduction in animals compare?- How do internal and external fertilization differ?
- Where do embryos develop?
- How are terrestrial vertebrates adapted to reproduction on land?
oviparous • ovoviviparous • viviparous • placenta • metamorphosis • nymph • pupa • amniotic egg • mammary gland
Outline Before you read, use the headings and key concepts in this lesson to make an outline about animal reproduction. As you read, add details to your outline.
THINK ABOUT IT Sexual reproduction can be dangerous. Just ask a male praying mantis—who may be devoured by his mate. Or a male peacock, whose success in courting a female depends on his growing and lugging around a huge tail that makes it harder for him to escape predators. Or a male emperor penguin, who incubates an egg for months on antarctic ice in temperatures far below zero. Or a female deer, who carries around the ever-increasing weight of her developing young for seven months, while she runs from predators such as coyotes and seeks food for herself and the young she carries. Yet, most animal species engage in sexual reproduction during at least part of their life cycles. Why?
Asexual and Sexual Reproduction
How do asexual and sexual reproduction in animals compare?
Many invertebrates and a few chordates can reproduce asexually.
Asexual Reproduction Animals reproduce asexually in many ways. Some cnidarians divide in two. Some animals reproduce through budding, which produces new individuals as outgrowths of the body wall. Females of some species, such as the whiptail lizard in Figure 28–14, can reproduce asexually by producing eggs that develop without being fertilized. This process is called parthenogenesis (pahr thuh noh JEN uh sis). Parthenogenesis produces offspring that carry DNA inherited only from their mothers. This means of reproduction occurs in some crustaceans and insects but very rarely in vertebrates.
Asexual reproduction requires only one parent, so individuals in favorable environmental conditions can reproduce rapidly. But since offspring produced asexually carry only a single parent's DNA, they have less genetic diversity than do offspring produced sexually. Lack of genetic diversity can be a disadvantage to a population if its environment changes.
FIGURE 28–14 Parthenogenesis Some whiptail lizard species reproduce exclusively by parthenogenesis. Infer Describe the degree of genetic diversity in these whiptail lizard species.
Table of Contents
- Formulas and Equations
- Applying Formulas and Equations
- Mean, Median, and Mode
- Estimation
- Using Measurements in Calculations
- Effects of Measurement Errors
- Accuracy
- Precision
- Comparing Accuracy and Precision
- Significant Figures
- Calculating With Significant Figures
- Scientific Notation
- Calculating With Scientific Notation
- Dimensional Analysis
- Applying Dimensional Analysis