Meiosis Worksheet (30 points)
Name:_________Gibson, John_________________________
(2 pts) Why is prophase I so important in meiosis?
Prophase I has crossing-over of paternal-maternal chromosomes. This increases the genetic diversity of the population.
Prophase I has the special kinetochore binding homolog chromosome centromeres, so the subsequent homolog separation can produce haploid cells.
This special kinetochore is different from mitosis kinetochore which only binds to a single centromere.
(3 pts) Compare and contrast mitosis and meiosis, use a table to describe how the phases are similar and/or different. Point out key events, chromosome number (you may focus on human cells), final products, genetic diversity, chromosomal alignment etc.
(2 pt) With regards to this lab/meiosis, how is genetic variation introduced into a population?
crossing-over at prophase 1, we switched tips of the pink-blue (paternal and maternal) pair and the green-orange pair
independent assortment at anaphase 1, we separate pink-blue pairs (paternal and maternal) independently from separating the green-orange pair and independently from separating the red-yellow pair
(1 pt) How are organelles and cytoplasm passed from one generation to the next in humans? (you may need to do some research)
Mitochondria have a circular DNA, so they replicate their DNA, in-sync with S-phase DNA replication of chromosomal DNA, likely by CDk and cyclin signals.
Cytoplasm is equally divided in mitosis with 2 spindle poles.
Cytoplasm is unequally divided in meiosis with 2 spindle poles.
Most of cytoplasm contents, comes from egg (ova), not from sperm.
(2 pts) Describe how meiosis reduces the number of chromosomes in each cell. Be specific to address what each cell contains at each phase of the process. Key terms to include are homologous chromosomes, sister chromatids, etc.
The number of chromosomes is halved at cytokinesis 1.
At prophase 1, the number of chromosomes are the same as parent, 46 chromosomes in human. Chromosome 1 from father, chromosome 1 from mother, chromosome 2 from father, chromosome 2 from mother,.... chromosome 23 from father, chromosome 23 from mother.
At cytokinesis 1, the number of chromosome per cell is half as parent, each cell has a homologous of a chromosome. For example, for cell one, chromosome 1 from father, chromosome 2 from mother, chromosome 3 from father, chromosome 4 from mother,... chromosome 23 from father.
For cell two, chromosome 1 from mother, chromosome 2 from father, chromosome 3 from mother, …
At anaphase 2, the sister chromatids split, but the number of chromosomes per pole does not decrease because sister chromatids are mainly identical if there is no crossing over. Some may argue that the number of chromosomes increases to form diploid cells, but the point is that no decreasing of number of chromosomes occurs in this phase.
Cells are haploids after Meiosis I.
(9 pts) Based on the modeling activity in lab, recreate figures 1-9 this time adding in microtubules, centromeres, the nuclear and plasma membranes. *this can be placed at the end of the document
(2 pts) At the end of meiosis I there are _____2____________ cells and these cells are ___haploid_____________.
(2 pts) Explain why the cell would not go into interphase again.
The product of Meiosis I is two cells of haploids.
In them, each chromosome is already replicated with sister chromatid pairs.
Interphase comprises G1, S, and G2 phases, where the G1 phase is licensed to replicate DNA.
There is no licensing during Meiosis 1 for sister chromatids to replicate.
Even if there is licensing to replicate sister chromatids, there is no kinetochore to hold 4 replications of DNA.
(2pts) Meiosis results in _____4______(number) daughter cells that are ____smaller, containing half the genetic material__________ than the parent cell.
(5 pts) Answer the following questions based on the karyotype assigned:
Does the individual have a trisomy or a monosomy?
Patau’s syndrome: Trisomy of chromosome 13.
Which chromosome is affected?
Chromosome 13
Does this condition have a common name?
Yes, it is often simply called Trisomy 13.
Do fetuses with this condition typically make it full term?
No, 90% die/terminated before birth. This high rate of fetal mortality largely is due to elective abortions, according to Barts and The London School of Medicine
“In 2008/9 there were 172 diagnoses of Patau and 495 diagnoses of Edwards syndrome, of which an estimated 18 and 37 respectively were live births. “
How common is it?
About 1/10,000 according to Cleveland Clinic
https://my.clevelandclinic.org/health/diseases/24647-trisomy-13-patau-syndrome
What are some common physical features of an individual with this disorder/syndrome?
Cleft lips, Cleft palate (hole between sinus and the roof of the mouth). Low setting ears. Bulbous nose.
What is the average life expectancy for an individual with the condition?
Less than one year.
“Only 5% to 10% of babies born with trisomy 13 survive past their first year.” in the same Cleveland Clinic article.
Is there gender specificity?
Not mentioned in many articles.
State (if it’s known) or propose how/where this might arise during Meiosis.
Not mentioned in many articles. Could be nondisjunction in either anaphase I/II.
Any other interesting facts/figures that you found
Parents report their Patau syndrome infant enriched their lives. These infants somehow appear to be more “happy” in disposition than regular infants, reported in https://publications.aap.org/pediatrics/article-abstract/130/2/293/29915/The-Experience-of-Families-With-Children-With?redirectedFrom=fulltext
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