CHAPTER 27 Reproduction and Embryonic Development Module 27.1

Mating Without Males There are no male desert-grassland whiptail lizards The species reproduces without copulation or fertilization

This photo shows a ritual behavior that primes a female to lay eggs The female on top behaves much like a male in other species of whiptail lizards Mating behavior seems to be an evolutionary leftover

Reptiles, birds, and mammals have four embryonic membranes Although the reproduction method of desert-grassland whiptails is unusual, their embryonic development is similar to all other animal species Reptiles, birds, and mammals have four embryonic membranes Chorion Embryo Amnion Allantois Yolk Yolk sac Shell

All animal species have three stages of embryonic development Mitotic cell division Cellular differentiation Formation of the body and its structures

27.1 Sexual and asexual reproduction are both common among animals ASEXUAL AND SEXUAL REPRODUCTION 27.1 Sexual and asexual reproduction are both common among animals Asexual reproduction Budding Fission Fragmentation, accompanied by regeneration Development of an unfertilized egg Figure 27.1A

Sexual reproduction The fission of two haploid gametes from two parents to form a diploid zygote Figure 27.1D

Rotifers can reproduce both asexually and sexually “Head” Intestine Ovary Eggs Hermaphroditism A single individual has both male and female reproductive systems Figure 27.1B, C

Advantages of asexual reproduction A single individual reproduces Many offspring are produced rapidly Disadvantage of asexual reproduction Little or no genetic variation

Advantages of sexual reproduction Increases genetic variation Enhances reproductive success in changing environments Disadvantage of sexual reproduction Locating a mate