Chapter 7Section 2: Sexual Reproduction

Grade 10 BiologyFall 2010

Objectives•Differentiate between asexual and sexual

reproduction•Identify three types of asexual

reproduction•Evaluate the relative genetic and

evolutionary advantages and disadvantages of asexual and sexual reproduction

•Differentiate between the three major sexual life cycles found in eukaryotes

Sexual and Asexual Reproduction•Reproduction: the process of producing

offspring, can be asexual or sexual

Sexual and Asexual Reproduction•Asexual reproduction: single parent

passes copies of all of its genes to each of its offspring ▫No fusion of haploid cells such as gametes

•Clone: individual produced by asexual reproduction, genetically identical to its parents

•Example: prokaryotes, binary fission ▫Do eukaryotes reproduce asexually?

Asexual Reproduction

Prokaryotes Eukaryotes

Sexual and Asexual Reproduction•Sexual reproduction: two parents each

form reproductive cells that ave one-half the number of chromsomes ▫Haploid gametes form diploid offspring▫“2 halves make a whole”

•Offspring have traits of both parents•Occurs in eukaryotes

Sexual Reproduction

Types of Asexual Reproduction•Fission:

separation of a parent into two or more individuals of about equal size ▫Prokaryotes

Types of Asexual Reproduction•Fragmentation: body breaks into several

pieces, fragments develop into complete adults▫Eukaryotes

Types of Asexual Reproduction•Budding: new individuals split off from

existing ones ▫Eukaryotes

Genetic Diversity•Asexual reproduction •Advantages:

▫Simplest and most primitive method of reproduction

▫Allows organism to produce many offspring with less energy

•Disadvantages:▫DNA varies little between individuals ▫Less adaptation abilities

Genetic Diversity•Sexual Reproduction:•Advantages:

▫Genetic variation •Disadvantages:

▫Takes more time and energy

Sexual Life Cycle in Eukaryotes•Life cycle: entire span in the life cycle of

an organism from one generation to the next

•Eukaryotes that undergo sexual reproduction can have one of three types of sexual life cycles:▫Haploid ▫Diploid ▫Alternation of generations

Haploid Life Cycle•Simplest of sexual life cycles •Haploid cells occupy the major portion of

the life cycle •Zygote: only diploid cell, undergoes

meiosis immediately after it is formed •Haploid cells give rise to haploid

multicellular individuals that produce gametes by mitosis (not meiosis)

•Process called fusion, gametes fuse to produce a diploid zygote, cycle continues

Haploid Life Cycle

Diploid Life Cycle•Adult individuals are diploid•Individuals inherit chromosomes from 2

parents•Diploid reproductive cell undergoes

meiosis to produce gametes •Gametes (sperm and egg) join in

fertilization ▫Results in diploid zygote

Diploid Life Cycle

Alternation of Generations •Alternates between haploid and diploid

phase•Occurs in plants, algae, and some protists

Alternation of Generations •In plants:•Sporophyte: diploid phase in the life cycle

that produces spores•Spore: haploid reproductive cell produced

by meiosis that is capable of developing into an adult without fusing with another cell▫Spore gives rise to a multicellular individual

called a gametophyte without joining with another cell

Alternation of Generations •Gametophyte: haploid phase that

produces gametes by mitosis ▫Gametes fuse and give rise to the diploid

phase •Sporophyte and gametohpyte generations

take turns, or alternate, in life cycle