Chapter 41 Animal Reproduction Lecture Outlines by Gregory Ahearn University of North Florida Copyright 2011 Pearson Education Inc Chapter 41 At a Glance 41 1 How Do Animals Reproduce 41 2 What Are the Structures and Functions of Human Reproductive Systems 41 3 How Can People Limit Fertility Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 41 1 How Do Animals Reproduce Animals reproduce either sexually or asexually In asexual reproduction a single animal produces offspring usually through repeated mitotic cell division in some part of its body The offspring are therefore genetically identical to the parent Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 41 1 How Do Animals Reproduce Animals reproduce either sexually or asexually continued In sexual reproduction organs called gonads produce haploid sperm or eggs through meiotic cell division A sperm and egg usually from separate parents fuse to produce a diploid fertilized egg that then undergoes repeated mitotic cell divisions to produce an offspring Because the offspring receives genes from both of its parents it is not genetically identical to either Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 41 1 How Do Animals Reproduce In asexual reproduction a single organism reproduces by itself Asexual reproduction is efficient in effort no need to search for mates court members of the opposite sex or battle rivals materials no wasted gametes and genes the offspring have all the genes of their parent Efficiency has probably been the driving force behind the evolution of a variety of methods of asexual reproduction Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 41 1 How Do Animals Reproduce Budding produces a miniature version of the adult A miniature version of the adult a bud grows directly on the body of the adult When it as grown large enough the bud breaks off and becomes independent Many sponges and cnidarians reproduce by budding Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 41 1 How Do Animals Reproduce Fission followed by regeneration can produce a new individual Many animals are capable of regeneration the ability to re grow lost body parts Regeneration is part of reproduction in species that reproduce by fission Some annelids flatworms corals sea jellies and brittle stars reproduce by division into two or more pieces each of which regenerates the missing parts of a complete body Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 41 1 How Do Animals Reproduce During parthenogenesis eggs develop without fertilization The females of some animal species can reproduce by a process known as parthenogenesis in which egg cells develop into viable offspring without being fertilized Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 41 1 How Do Animals Reproduce In some species parthenogenetically produced offspring are haploid For example male honeybees develop from unfertilized haploid eggs and remain haploid their diploid sisters develop from fertilized eggs Some parthenogenetic fish amphibians and reptiles produce diploid offspring by doubling the number of chromosomes in the eggs either before or after meiosis Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 41 1 How Do Animals Reproduce In some species parthenogenetically produced offspring are haploid continued In most species all the resulting diploid offspring are female In fact some species of fish and some lizards such as the whiptail of the southwestern United States and Mexico have populations consisting entirely of parthenogenetically reproducing females Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 41 1 How Do Animals Reproduce In some species parthenogenetically produced offspring are haploid continued Still other animals such as some aphids can reproduce either sexually or parthenogenetically depending on environmental factors such as the season of the year and the availability of food Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 41 1 How Do Animals Reproduce Sexual reproduction requires the union of sperm and egg No one is certain why sexual reproduction evolved in the first place or why natural selection has made it by far the most common form of reproduction in animals Sex does have one important outcome The genetic recombination that results from sexual reproduction creates novel genotypes and therefore novel phenotypes that are an important source of variation upon which natural selection may act Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 41 1 How Do Animals Reproduce In most animals species an individual is either male or female defined by the type of gamete that each produces The female gonad called the ovary produces eggs that are large nonmotile haploid cells containing food reserves that provide nourishment for the embryo an offspring in its early stages of development before birth or hatching The male gonad called the testis plural testes produces small motile haploid sperm which have almost no cytoplasm and hence no food reserves Fertilization the union of sperm and egg forms a diploid zygote Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 41 1 How Do Animals Reproduce In some animals such as earthworms and many snails single individuals produce both sperm and eggs Such individuals are called hermaphrodites they still engage in sex with two individuals exchanging sperm Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 41 1 How Do Animals Reproduce Some hermaphrodites however can fertilize their own egg These animals including tapeworms and some types of snails are often relatively immobile and may find themselves isolated from other members of their species Self fertilization is advantageous under these circumstances For species with two separate sexes and hermaphrodites that cannot self fertilize successful reproduction requires that sperm and eggs from different animals be brought together for fertilization Biology Life on Earth 9e Copyright 2011 Pearson Education Inc 41 1 How Do Animals Reproduce External fertilization occurs outside the parents bodies In external fertilization sperm and egg unite outside the bodies of the parents Sperm and eggs are typically released into water a process called spawning and the sperm swim to reach the eggs Because sperm and eggs are relatively short lived spawning animals must synchronize their reproductive behaviors both temporally
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