Chapter 7 Section 2: Sexual Reproduction Grade 10 Biology Fall 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 ProkaryotesEukaryotes

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