Biology 1A    Oct 1, 1998
Lecture 10 - Sexual Reproduction

Page Contents :

• Reading Assignment
• Overview of Lecture
• Overview of Lab
• Lecture Outline
• Vocabulary
• Study Questions
• Related Websites

Stern: Chapter 12

Overview of Lecture:

Sexual reproduction requires both meiosis and syngamy.
     Meiosis is a reduction division.
     Syngamy is a fusion of gametes.
Variation in sexual life cycles.
     Diploid life cycles.
     Haploid life cycles.
     Alternation of generations.
     Separation of the sexes.
Many organisms reproduce asexually.
Reproduction and dispersal are not the same.

Overview of Lab:

(A bullet indicates a handout.)
• Studying plant life cycles with the C-Fern.
  Stages of the fern life cycle.

A. Sexual reproduction is an extended process, defined by meiosis and syngamy.
B. Meiosis is a reduction division.
1. Division which turns a single diploid cell into four haploid cells.
2. Meiosis begins by separating homologous pairs of chromosomes
3. The second meiotic division happens much like mitosis
4. The net result of meiosis is four haploid cells.
C. Syngamy is a fusion of gametes.
1. Gametes are haploid cells exchanged in sexual reproduction
2. Kinds of gametes:
a. isogamy - both gametes identical; often flagellated
b. anisogamy - one gamete is larger; both usually flagellated
c. oogamy - one gamete is large and non-motile; one gamete is small and motile
3. Syngamy is the fusion of two haploid cells to make a diploid cell (zygote).
D. Summary
1. Meiosis : 1 diploid --> 4 haploid
2. Syngamy : 2 haploid --> 1 diploid

A. Diploid life cycles.
B. Haploid life cycles.
C. Alternation of generations
1. There is both a haploid and diploid multicellular stage, i.e. there is a haploid organism and a diploid organism.
2. The haploid organism is the gametophyte.
3. The diploid organism is the sporophyte.
4. Examples: many algae; all plants
5. May be hidden or hard to find in plants, but always present.
6. Alternation between generations can be: heteromorphic or isomorphic
D. Separation of the sexes - In any of these life cycles, there may be separation of duties into different sexes.

A. Asexual reproduction occurs without using both meiosis and syngamy.
B. Reproduction through vegetative growth.
1. Most plants, algae, and fungi have a modular construction of repeated units.
2. As such, they can undergo fragmentation.
C. Circumventing sex - agamospermy

A. Reproduction is the generation of new individuals.
B. Dispersal is the scattering of offspring

• What two processes must occur to complete sexual reproduction?
• Why is meiosis called a "reduction division"?
• At what point during meiosis does crossing-over occur? Why is crossing-over important?
• What is the difference between a haploid cell and a diploid cell?
• What are homologous chromosomes?
• What are gametes? What is the ploidy of the nucleus in a gamete? What happens when two gametes fuse together?
• Compare and contrast: isogamy, anisogamy, & oogamy. What are some examples of organisms that have each kind of gamete production?
• How might oogamy affect reproductive biology? That is, what are the consequences of having only one of the gamete pair motile, while the other is non-motile?
• Which of the following are characteristic of plants? of fungi? of both?

     sperm            syngamy             hyphae
     archegonia       dikaryon            diploid cells
     oogamy           sporophyte          zygote
     embryo           multicellularity    spores
  

• Why does sexual reproduction require both meiosis and syngamy?
• What are the products of meiosis in a diploid life cycle? in a haploid life cycle? in an alternation of generations?
• What are the products of syngamy in a diploid life cycle? in a haploid life cycle? in an alternation of generations?
• In which kind of sexual life cycle(s) does the zygote develop into an embryo? In which does it undergo meiosis directly?
• How is an ascomycete or basidiomycete life cycle different from the typical haploid life cycle? What causes this difference?
• What kind of life cycle do slime molds have? humans? ferns? algae?
• Compare and contrast the sporophyte and gametophyte of the fern.
• What does it mean to be male? to be female?
• Can a sporophyte plant be male or female? Why or why not?
• What are some examples of asexual reproduction by fragmentation?
• Why is fragmentation more common in plants than in animals?
• Define both reproduction and dispersal, and explain the difference between them.

• UCMP Glossary Vol. 6 : Life History