chapter 2 - chromosomes & cellular reproduction

prokaryotic cell nucleus

absent

prokaryotic cell diameter

relatively small, from 1 to 10 um, 10-100x smaller than eukaryotes

prokaryotic cell genome

usually one circular DNA molecule

prokaryotic cell DNA

not complexed with histones in bacteria; some histones in archaea

prokaryotic cell amount of DNA

relatively small

prokaryotic cell membrane-bounded organelles

absent

eukaryotic cell nucleus

present

eukaryotic cell diameter

relatively large, from 10 to 100 um

eukaryotic cell genome

multiple linear DNA molecules

eukaryotic cell DNA

complexed with histones

eukaryotic cell amount of DNA

relatively large

eukaryotic cell membrane-bounded organelles

present

prokaryotes

no histones, unicellular, made up of eubacteria and archaea

prokaryotic DNA

does not exist in the highly ordered and packed arrangement

archaea

extremists = high or low pH, high or low temperatures, salty environments

eukaryotes

both unicellular and multicellular with membrane-bound organelles

genetic material is surrounded in a nuclear envelope to form a nucleus

DNA is closely associated with histones to form tightly packed chromosomes

bacteria and archaea are…

prokaryotes

viruses

neither prokaryotic nor eukaryotic

outer protein coat surrounding nucleic acid, DNA or RNA

viruses require a host

kill the host, bacteriophages, invade & hijack

simple division

separation of replicated circular chromosome

prokaryotic cell reproduction

simple division, origin of replication, high rate of replication

eukaryotic chromosomes

homologous pairs

chromosome structure

cell cycle

genetic consequences of the cell cycle

diploid cells

carry two sets of genetic variation

haploid cells

carry one set of genetic information

gametes (sperm and egg)

plants (polyploid)

allele

different version of a gene at a certain locus

2n

diploid

n

haploid

centromere

attachment point for spindle microtubules (pull apart)

connects the two sister chromatids

telomeres

tips of a linear chromosome

buffer, protect from shortening

origins of replication

where the DNA syntheses begin

centromeres are not…

always in the middle

no kinetochore….

spindle microtubules would not attach to the chromosome

no kinetochore…

the chromosome would not be drawn into a newly formed nucleus

no kinetochore…

resulting daughter cells would be missing a chromosome

interphase

an extended period between cell divisions, DNA synthesis, and chromosome replication phase

90%

mitotic phase

M phase, 10%

phase checkpoints

key transition points

G₁

growth; proteins necessary for cell division synthesized

G₁ / S checkpoint

regulated decision point

S

DNA synthesis

G₂

biochemical preparation for cell division

G₂ / M checkpoint

only passed if DNA is completely replicated and undamaged

mitosis

separation of sister chromatids

cytokinesis

separation of cytoplasm, cytoplasm divides; cell wall forms in plant cells

G₀ phase

stable, nondividing period of variable length

prophase

chromosomes condense and mitotic spindle forms

prometaphase

nuclear envelope disintegrates, and spindle microtubules anchor to kinetochores

metaphase

chromosomes align on the metaphase plate; spindle-assembly checkpoint

anaphase

sister chromatids separate, becoming individual chromosomes that migrate toward spindle poles

telophase

chromosomes arrive at spindle poles, the nuclear envelope re-forms, and the condensed chromosomes relax

cycle produces two cells that are genetically identical to each other…

and with the cell that gave rise to them

newly formed cells contain a…

full complement of chromosomes

each newly formed cell contains approximately half…

the cytoplasm and organelle content of the original parental cell

meiosis

the production of haploid gametes

fertilization

the fusion of haploid gametes

genetic variation

consequences of meiosis

interphase

DNA synthesis and chromosome replication phase

meiosis I

separation of homologous chromosome pairs, and reduction of the chromosome number by half

4 haploid daughter cells

meiosis II

separation of sister chromatids, also known as equational division

prophase I

synapsis, tetrad, crossing over

synapsis

close pairing of homologous chromosomes

tetrad

closely associated four-sister chromatids of two homologous chromosomes

crossing over

crossing over of chromosome segments from the sister chromatid of one chromosome to the sister chromatid of the other synapsed chromosome

exchange of genetic information, the first mechanism of generating genetic variation in newly formed gamete

metaphase I

random alignment of homologous pairs of chromosomes along the metaphase plate

anaphase I

separation of homologous chromosome pairs, and the random distribution of chromosomes into two newly divided cells

second mechanism of generating genetic variation in the newly formed gametes

telophase I

nuclear envelope reforms

interkinesis

the period between meiosis I and meiosis II

which event takes place in meiosis II but not in meiosis I?

separation of chromatids

how many cells are produced from each original cell in meiosis?

4

in meiosis, the chromosome number in each new cell is…

reduced by half, 2n to n

cohesion

a protein that holds the chromatids together and is key to the behavior of chromosomes in mitosis and meiosis

how does shugoshin affect sister chromatids in meiosis I and meiosis II?

During anaphase I: Shugoshin protects cohesin at the centromeres from the action of separase.

During Anaphase II: – Shugoshin breaks down.

spermatogenesis

male gamete production

oogenesis

female gamete production

a secondary spermatocyte has 12 chromosomes. how many chromosomes will be found in the spermatogonium that gave rise to it?

24

which structure is diploid?

microsphorophyte

through which process can plants still have genetic variation when they self-cross (i.e., asexually reproduce)?

recombination