Reproduction - Reproduction Introduction Reproduction is...

Info icon This preview shows pages 1–10. Sign up to view the full content.

View Full Document Right Arrow Icon
Reproduction
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Introduction Reproduction is the essential goal of every organism. Understanding and manipulating reproductive systems is an important issue for physicians, veterinarians, farmers, zookeepers, and many others in biology-related professions.
Image of page 2
Asexual and Sexual Reproduction Asexual reproduction is based on mitosis and results in offspring that are genetically identical to one another and to their parent. Sexual reproduction is based on meiosis and fusion of gametes. Genetic recombination during meiosis and the fusion of haploid gametes from different parents during fertilization result in offspring that are genetically different from one another and from their parents.
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
How Does Asexual Reproduction Occur? ANIMALS: In budding , an offspring begins to form within or on a parent; the process is completed when the offspring breaks free and begins to grow on its own. The offspring is a miniature version of the parent. In fission , an individual simply splits into two or more descendants. In parthenogenesis , female offspring develop from unfertilized eggs. These offspring are genetically identical to the mother.
Image of page 4
Figure 50.1 (a) Budding in hydra Unfertilized eggs develop into offspring 5 mm (b) Fission in anemones (c) Parthenogenesis in lizards 5 cm Bud
Image of page 5

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Switching Reproductive Modes: A Case History Many animal species regularly switch between reproducing asexually and sexually. For example, Daphnia are crustaceans that reproduce both asexually and sexually in a typical year. Throughout the spring and summer, Daphnia produce only diploid female offspring by parthenogenesis. In late summer/early fall, however, many females begin producing male offspring. Haploid sperm from these males fuse with haploid eggs that females produce by meiosis during fertilization .
Image of page 6
Switching Reproductive Modes: A Case History In spring, the sexually produced offspring hatch and begin reproducing asexually. Daphnia were shown to require three different cues from the environment to switch to sexual reproduction: crowding, low food availability, and short day lengths. Scientists hypothesize that genetically variable offspring have higher fitness in rapidly changing environments.
Image of page 7

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
(a) Sexual reproduction is more common in crowded populations of Daphnia pulex than in sparse populations. (b) In Daphnia magna , which environmental cues trigger the switch to sexual reproduction?
Image of page 8
Mechanisms of Sexual Reproduction: Gametogenesis The mitotic cell divisions, meiotic cell divisions, and developmental events that result in the production of male and female gametes, or sperm and eggs, are collectively called gametogenesis . Spermatogenesis is the formation of sperm, and oogenesis is the formation of eggs.
Image of page 9

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 10
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern