25  •  Reproduction and Development 1003

From two parents to one embryo to one baby

How do animals reproduce? 1004

25.1

Reproductive options (and ethical issues) are on the rise. 1004

25.2

There are costs and benefits to having a partner: sexual versus asexual reproduction. 1005

25.3

Fertilization can occur inside or outside a female’s body. 1007

Male and female reproductive systems have important similarities and differences. 1010

25.4

Sperm are made in the testes. 1010

25.5

There is unseen conflict among sperm cells. 1013

25.6

This is how we do it: Can males increase sperm investment in response to the presence of another male? 1014

25.7

Eggs are made in the ovaries (and the process can take decades). 1016

25.8

Hormones direct the process of ovulation and the preparation for gestation. 1018

Sex can lead to fertilization, but it can also spread sexually transmitted diseases. 1022

25.9

In fertilization, two cells become one. 1022

25.10

Numerous strategies can help prevent fertilization. 1023

25.11

Sexually transmitted diseases reveal battles between microbes and humans. 1025

Human development occurs in specific stages. 1027

25.12

Early embryonic development occurs during cleavage, gastrulation, and neurulation. 1027

25.13

How does an embryo become male or female? 1030

25.14

There are three stages of pregnancy. 1032

25.15

Pregnancy culminates in childbirth and the start of lactation. 1034

Reproductive technology has benefits and dangers. 1036

25.16

Assisted reproductive technologies are promising and perilous. 1036

StreetBIO: KNOWLEDGE YOU CAN USE

Business and science in conflict: why is the number of multiple births—twins, triplets, and more—on the rise? 1038