Download
1 / 10
E N D
Reproduction • A defining feature of living things is that they can reproduce. Most animals reproduce sexually, but a few reproduce asexually. Different species may undergo very different processes and behaviors during reproduction, but all are adapted in various ways to ensure that offspring will be produced and will survive. • 1. For the aspects of reproduction listed below, explain which item in the pair is more likely to ensure the successful production or survival of more offspring: • Eggs fertilized outside the body VS eggs fertilized within the body • *Make sure to rewrite the questions in the space provided
Lesson Overview 28.3 Reproduction
THINK ABOUT IT • Sexual reproduction can be dangerous. • Just ask a male praying mantis—who may be devoured by his mate. Or an emperor penguin, who incubates an egg for months on Antarctic ice in temperatures far below zero. Or a female deer, who carries around her developing young for six months, while she runs from predators 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? • 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. • Sexual reproduction maintains genetic diversity in a population by creating individuals with new combinations of genes.
Mammalian Reproductive Strategies • Mammals have evolved various adaptations for reproducing and caring for their young. • The three groups of mammals—monotremes, marsupials, and placentals—differ greatly in their means of reproduction and development, but all nourish their young with mother’s milk.
Monotremes • Reproduction in monotremes, such as the echidna, combines reptilian and mammalian traits. • Like a reptile, a female monotreme lays soft-shelled, amniotic eggs that are incubated outside her body. The eggs hatch in about ten days. • But like other mammals, young monotremes are nourished by milk produced by the mother’s mammary glands. • Female monotremes secrete milk through pores on the surface of the abdomen.
Marsupials • Marsupials, such as wallabies, bear live young that usually complete their development in an external pouch. • Marsupial young are born at a very early stage of development. Little more than embryos, they crawl across their mother’s fur and attach to a nipple in her pouch, or marsupium. • Inside the marsupium, the young spend months attached to a nipple, drinking milk and growing inside until they can survive independently.
Placentals • Placental mammals are nourished through a placenta before they are born and by their mother’s milk after they are born.The placenta allows the embryo to develop for a long time inside the mother, and to be born at a fairly advanced stage of development. • Placental mammals are nourished through a placenta before they are born.
