Principles of Zoology I
www.noolmusic.com
11th Principle of Evolution: in eukaryotes, nuclear
DNA is organized into chromosomes
Fig. 3.4
Sexual
Reproduction
Each parent
provides a
haploid
chromosome set
Fig. 11.2
Chromosomes pair when gametes fuse
(fertilization): new genome.
Fig. 11.1
Homologous chromosomes (diploidy):
one copy from each parent (genome)
http://www.wellcome.ac.uk
Meiosis (gamete production)
Occurs in germ-line cells (reproductive organs)
http://www.potosisd.k12.wi.us/
Gamete: a haploid cell; functions in sexual
reproduction (no homologous chromosomes)
http://www.intechopen.com/
http://www.ib.bioninja.com.au/
Meiosis
Gamete
formation
As in mitosis, nuclear DNA is replicated prior to meiosis
http://upload.wikimedia.org/
Duplicated
chromosome
www.plyojump.com
Meiosis I
Prophase I
Spindle apparatus assembles
Nuclear envelope breakdown
www.monteweston.com
Meiosis I: Prophase I
Homologous chromosomes visible & paired
Crossing over (recombination)
www.monteweston.com
Prophase I
Homologous chromosomes pair (synapsis)
Fig. 11.3
Prophase I
Crossing over (non-sister chromatids): homologous
chromosomes exchange DNA segments
www.uic.edu
In-class writing: how does crossing over
contribute to uniqueness of genomes among
gametes?
http://upload.wikimedia.org/
Crossing over:
creates “new”
chromosomes!
faculty.ircc.edu
Metaphase I: Chromosomes align with inner-cell
circumference
http://botit.botany.wisc.edu/
Metaphase I: Chiasmata bind homologous chromosomes
http://lycee.nicolas-cohen.org/
Metaphase I: Kinetochores attach modified sister
chromatids to the same pole
faculty.clintoncc.suny.edu
Metaphase I: Independent assortment:
homologous, duplicated chromosome pairs orient
randomly towards poles
http://www.dlt.ncssm.edu/
In-class writing: how does independent
assortment contribute to uniqueness of
genomes among daughter cells?
http://prod-media-output.s3-website-us-west-1.amazonaws.com/
Independent assortment: creates “new” chromosome
combinations (mix from parents)!
http://zebrafish.umdnj.edu
Meiosis I: Anaphase I
Homologous (duplicated) chromosomes separate
www.monteweston.com
Meiosis I
Anaphase I – modified homologues pulled apart
http://jcs.biologists.org/
Meiosis I
Telophase I
Nuclear envelope reforms
Cytokinesis
www.monteweston.com
Are daughter cells
haploid or diploid
when Meiosis I
ends?
http://www.vce.bioninja.com.au/
Haploid vs. diploid refers to homologous
chromosomes (not duplicated chromosomes)!
https://bio.rutgers.edu
Meiosis I: reduction division
www.monteweston.com
Homologous chromosomes separate in Meiosis 1!
http://dc721.4shared.com/
Sister chromatids stay together in meiosis I!
http://kvhs.nbed.nb.ca/
In-class review: how does meiosis I differ from mitosis?
http://pad1.whstatic.com/
Meiosis I versus Mitosis:
Sister chromatids “connected” in meiosis I
Textbook pages 210 - 211
Meiosis I versus Mitosis:
http://pad1.whstatic.com/
Fig. 11.4
Meiosis II
Proceeds without additional DNA replication (suppression)
https://sites.google.com
Prophase II
Chromosomes visible
Spindle apparatus assembles
Nuclear envelope breakdown
www.monteweston.com
Metaphase II
Chromosomes align
Kinetochores attach
www.monteweston.com
Anaphase II
Centromeres split
Sister chromatids pulled to opposite poles
Poles move apart
www.monteweston.com
Telophase II
Spindle apparatus disassembles
Nuclear envelope forms
Chromosomes uncoil
www.monteweston.com
Are daughter cells haploid or diploid when
Meiosis II ends?
http://pad2.whstatic.com/
Haploid daughter cells are unique & lack
homologous chromosomes
Fig. 11.7
Gametes carry only one,
non-duplicated, copy of
each chromosome…
Modified!
http://www.vce.bioninja.com.au/
Each new genome is potentially a unique mix of
modified chromosomes from both parents!
http://www.vce.bioninja.com.au/
Gamete fusion: genome formation
labspace.open.ac.uk
http://4.bp.blogspot.com/
External
Fertilization
http://www.an-creagan.com/
http://2.bp.blogspot.com/
Internal
Fertilization
www.albion.edu
In-class review: describe key differences of the chromosomes
& genome of a new diploid zygote versus its parents.
http://alphascientists.org/