Chapter 7 MeiosisChapter 7 Meiosis

Meiosis Meiosis

Forms haploid gamete or spore Forms haploid gamete or spore cellscells

Type of cell division that halves Type of cell division that halves the number of chromosomesthe number of chromosomes

Creates 4 genetically different Creates 4 genetically different cellscells

Steps to Meiosis ISteps to Meiosis I

Prophase I – Chromosomes condense, Prophase I – Chromosomes condense, nuclear membrane breaks down, nuclear membrane breaks down, homologous chromosomes pair up and homologous chromosomes pair up and crossing-overcrossing-over occurs occurs

Crossing-overCrossing-over – when homologous – when homologous chromosome pairs exchange genetic chromosome pairs exchange genetic materialmaterial

http://www.zerobio.com/crossing_over.htmhttp://www.zerobio.com/crossing_over.htm

Metaphase IMetaphase I

Pairs of homologous chromosomes line up Pairs of homologous chromosomes line up together (like holding hands)together (like holding hands)

Anaphase IAnaphase I

Pairs separate (NOT CHROMATIDS) and Pairs separate (NOT CHROMATIDS) and are pulled to opposite ends of the cellare pulled to opposite ends of the cell

Telophase ITelophase I

Chromosomes gather at the polesChromosomes gather at the poles Cytokinesis then occursCytokinesis then occurs DNA does not replicate to start Meiosis IIDNA does not replicate to start Meiosis II

Prophase IIProphase II

New spindle formsNew spindle forms

Metaphase IIMetaphase II

Chromosomes line up along the middle of Chromosomes line up along the middle of the cell (just like Mitosis)the cell (just like Mitosis)

Anaphase IIAnaphase II

Centromeres divide, chromatids separate, Centromeres divide, chromatids separate, and move towards the poles of the celland move towards the poles of the cell

Telophase II – Nuclear membrane forms Telophase II – Nuclear membrane forms around each set of chromosomes around each set of chromosomes

Cytokinesis occursCytokinesis occurs

http://highered.mcgraw-hill.com/sites/http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/0072437316/student_view0/chapter12/animations.html#animations.html#

http://www.johnkyrk.com/meiosis.htmlhttp://www.johnkyrk.com/meiosis.html

Genetic DiversityGenetic Diversity

Meiosis contributes to genetic Meiosis contributes to genetic diversitydiversity

Makes sure all organisms are Makes sure all organisms are genetically differentgenetically different

Independent AssortmentIndependent Assortment

The random distribution of The random distribution of homologous chromosomes during homologous chromosomes during MeiosisMeiosis

Crossing-OverCrossing-Over

DNA exchanged between DNA exchanged between homologous chromosomes during homologous chromosomes during Prophase IProphase I

Random FertilizationRandom Fertilization

Random sperm cell fuses with a Random sperm cell fuses with a random egg cellrandom egg cell

http://biog-101-104.bio.cornell.edu/http://biog-101-104.bio.cornell.edu/BioG101_104/tutorials/cell_division/BioG101_104/tutorials/cell_division/CDCK/cdck.htmlCDCK/cdck.html

OogenesisOogenesis

Process that creates female egg cellsProcess that creates female egg cells Of the four haploid cells created Of the four haploid cells created

during Meiosis, three will die as polar during Meiosis, three will die as polar bodies and one will survive as an egg bodies and one will survive as an egg cellcell

SpermatogenesisSpermatogenesis

Process that creates male sperm Process that creates male sperm cellscells

All four haploid gamete cells will All four haploid gamete cells will develop into sperm cellsdevelop into sperm cells

7-2 Sexual Reproduction7-2 Sexual Reproduction

Asexual – One parentAsexual – One parent Creates offspring that are clonesCreates offspring that are clones Sexual Reproduction – two parentsSexual Reproduction – two parents Creates genetically different offspringCreates genetically different offspring

Advantages for EachAdvantages for Each

Asexual allows organisms to produce Asexual allows organisms to produce many offspring in a short amount of many offspring in a short amount of timetime

Sexual reproduction creates genetic Sexual reproduction creates genetic diversitydiversity

Disadvantages for BothDisadvantages for Both

Asexual creates very little genetic Asexual creates very little genetic diversitydiversity

Sexually reproducing organisms Sexually reproducing organisms depend on finding mates (takes time depend on finding mates (takes time and NRG)and NRG)

Alternation of GenerationsAlternation of Generations

Organisms cycle through diploid and Organisms cycle through diploid and haploid life stageshaploid life stages

Haploid Life Cycle – haploid cells Haploid Life Cycle – haploid cells occupy the major portion of the life occupy the major portion of the life cycle (protists, fungi)cycle (protists, fungi)

Diploid Life Cycle - adult individuals are Diploid Life Cycle - adult individuals are diploid, gametes are the only haploid cells diploid, gametes are the only haploid cells (animals)(animals)

Alternation of Generations – plants, algae, Alternation of Generations – plants, algae, and some protists alternate between a and some protists alternate between a haploid and diploid phasehaploid and diploid phase

Sporophyte – diploid phase when spores Sporophyte – diploid phase when spores are madeare made

Gametophyte - haploid phase where Gametophyte - haploid phase where gametes are madegametes are made