0.5 mm
Parent
Bud
(a) Hydra (b) Redwoods 1
5 µm
Pair of homologous replicated chromosomes
Centromere
Sister chromatids Metaphase chromosome
2 Key Maternal set of chromosomes (n = 3) 2n = 6 Paternal set of chromosomes (n = 3)
Two sister chromatids of one replicated chromosome Centromere
Two nonsister Pair of homologous chromatids in chromosomes a homologous pair (one from each set)
3
Key Haploid gametes (n = 23) Haploid (n) Egg (n) Diploid (2n)
Sperm (n) MEIOSIS FERTILIZATION
Ovary Testis Diploid zygote (2n = 46)
Mitosis and development
Multicellular diploid adults (2n = 46) 4 Key Haploid (n) Haploid multi- Haploid unicellular or Diploid (2n) multicellular organism cellular organism (gametophyte) n Gametes n
n Mitosis n Mitosis Mitosis n Mitosis n n n n n MEIOSIS FERTILIZATION Spores n n Gametes Gametes n MEIOSIS FERTILIZATION
Zygote MEIOSIS FERTILIZATION 2n 2n 2n 2n Diploid Diploid Zygote 2n multicellular Mitosis multicellular organism Mitosis organism Zygote (sporophyte)
(a) Animals (b) Plants and some algae (c) Most fungi and some protists
5
Interphase Homologous pair of chromosomes in diploid parent cell
Chromosomes replicate Homologous pair of replicated chromosomes
Sister chromatids Diploid cell with replicated chromosomes
Meiosis I
1 Homologous chromosomes separate Haploid cells with replicated chromosomes Meiosis II
2 Sister chromatids separate
Haploid cells with unreplicated chromosomes 6 Telophase I and Telophase II and Prophase I Metaphase I Anaphase I Prophase II Metaphase II Anaphase II Cytokinesis Cytokinesis
Centrosome (with centriole pair) Sister chromatids remain attached Centromere Sister Chiasmata (with kinetochore) chromatids Spindle Metaphase plate
Sister chromatids separate Haploid daughter cells forming Homologous Homologous Cleavage chromosomes chromosomes furrow separate Fragments Microtubule of nuclear attached to envelope kinetochore
7
MITOSIS MEIOSIS
MEIOSIS I Parent cell Chiasma Chromosome Chromosome Prophase replication replication Prophase I Homologous chromosome Replicated chromosome 2n = 6 pair
Metaphase Metaphase I
Anaphase Anaphase I Telophase Telophase I Haploid n = 3 Daughter cells of meiosis I 2n 2n MEIOSIS II
Daughter cells n n n n of mitosis Daughter cells of meiosis II 8 SUMMARY
Property Mitosis Meiosis
DNA Occurs during interphase before Occurs during interphase before meiosis I begins replication mitosis begins Number of One, including prophase, metaphase, Two, each including prophase, metaphase, anaphase, and divisions anaphase, and telophase telophase
Synapsis of Does not occur Occurs during prophase I along with crossing over homologous between nonsister chromatids; resulting chiasmata chromosomes hold pairs together due to sister chromatid cohesion
Number of Two, each diploid (2n) and genetically Four, each haploid (n), containing half as many chromosomes daughter cells identical to the parent cell as the parent cell; genetically different from the parent and genetic cell and from each other composition Role in the Enables multicellular adult to arise from Produces gametes; reduces number of chromosomes by half animal body zygote; produces cells for growth, repair, and introduces genetic variability among the gametes and, in some species, asexual reproduction
9
Possibility 1 Possibility 2
Two equally probable arrangements of chromosomes at metaphase I
Metaphase II
Daughter cells Combination 1 Combination 2 Combination 3 Combination 4
10 Prophase I Nonsister of meiosis chromatids Pair of held together homologs during synapsis
Chiasma
Centromere
TEM Anaphase I
Anaphase II
Daughter cells Recombinant chromosomes 11