Mitosis and Meiosis answers
Supplemental Instruction
Iowa State University / Leader: / Courtney
Course: / Bio211
Instructor: / Boury
Date: / 10/17/12
1) Compare and contrast Prokaryotic cell division and Eukaryotic cell division
Prokaryote:
Binary fission, DNA replicates, cell splits, asexual
Very fast
DNA in nucleoid region
Eukaryotic cell:
DNA in nucleous
Slower
Sexual (includes meiosis)
2) Draw three pairs of homologous chromosomes. What makes 2 chromosomes homologous? How are chromosomes organized into a karyotype? Are organisms with homologously paired chromosomes haploid or diploid?
Homologous= derived from the same chromosomes. Similar pair
Chromosomes are organized in a karyotype by size (karyotype is a photographic representation of the chromosomes)
diploid
3) How do autosomes differ from sex chromosomes? How many pairs of sex chromosomes do humans have? How many pairs of autosomes do humans have?
Autosomes- all other chromosomes (22)
Sex chromosomes – determine the sex of the individual (XorY)
Humans have 23 paired chromosomes and 46 chromosomes
4) Draw a metacentric, acrocentric and telocentric chromosome.
5) Draw the eukaryotic cell cycle. Label G1, S, G2 and M phase. What happens during each phase of interphase (G1, S, G2)? What are checkpoints and why are they important? What is being checked at each of these checkpoints? What is Go phase?
Cell grows and copies its chromosomes in preparation for cell division
G0=cells exit the cell cycle and postpone making the decision to divide
G1- recovery, make cell components. Will synthesize what was lost to the other cell. growth
S- synthesize DNA. Chromosomes are replicated. Sister chromatids will pair off. Cell has twice as many chromatidas as the number of chromosomes in g1phase
G2- readyness prepare for cell division. Synthesizes proteins that are necessary for chromosome sorting and cell division
M phase– mitosis and cytokinesis. Divide 1 cell into 2 nuclei
Checkpoints are regulated to make sure the conditions are appropriate for the cell to divide
Cyclins- protein responsible for advancing a cell through the phases for the cell by binding to a cyclin dependent kinase
Cyclin-dependent kinases-bind to cyclins to activate
G1 checkpoint= restriction checkpoint- determines if conditions are favorable for cell division for cell division and if the DNA is damaged. G1 cyclin is made in response to sufficient nutrients and growth factors
G2 checkpoint= checks for DNA damage, determines if all of the DNA is replicatd and moniters the levels of proteins needed for Mphase
Metaphase checkpoint= determines if all chromosomes are attached to the spindle apparatus
6) Explain what is happening at each step:
Interphase- prior to mitosis, includes G1, S, and G2 phases. Chromosomes have replicated . chromosomes are in nucleus
Prophase- start of mitosis, Chromosomes condense and, sister chromatids join to make chromosomes. Mitotic spindle starts to form. Centrioles appear. Nuclear envelope begins to disassociate
Prometaphase-nuclear membrane fragments. Mitotic spindle is fully formed sister chromatids attach to the spindle via kinetochore microtubules
Metaphase- pairs of sister chromatids are aligned in a single row along the metaphase plate
Anaphase-sister chromatids separate and migrate toward the poles as kinetochore microtubules shorten.
Telophase-chromosomes de-condense and the nuclear envelope re-forms. Cytokinesis occurs and separates the mother cell into 2 daughter cells
7) What is Cytokinesis. How does plant cell cytokinesis differ from animal cell cytokinesis?
Separate mother cell into 2 daughter cells
Cleavage furrow, animals
Cell plate, plants
8) How did Masui and Market discover MPF? Why did the researchers use three groups of frog oocytes? Why didn’t the 2-hour progesterone exposure cytoplasm make the recipient cell move to mitosis? Why did the 12-hour exposure cytoplasm trigger mitosis in the recipient cell?
What are the factors that promote cell division?
Used oocytes-mature into eggs
Progesterone- signaling molecule that induces the synthesis of factors that advance cells through the cell cycle from G2 to Mphase
Exposed oocytes to progesterone for 2 or 12 hours and no progesterone
Found exposure of oocytes to progesterone for 12 hours results in the synthesis of factors that advances oocytes from G2 to M.
One factor is the MPF maturation promoting factor which is activated by progesterone
9) Briefly describe meiosis
meiosis is diploid somatic cells haploid gametes
chromosomes replicate during s phase and condense at the start of meiosis
homologous chromosomes line up in pairs
homologous chromosomes separate 2 cells
sister chromatids separate (1N) 4 cells
10) What is crossing over? When does it occur?
Crossing over is the exchange of chromosome parts of the tetrad. Creates the diversity and genetic variation.
Prophase 1
10) Compare mitosis and meiosis (1&2)