STUDY GUIDE
LAB: Meiosis and Non-disjunction
1. Explain how meiosis is different from mitosis…
Mitosis
Meiosis
Are cells an exact copy of the parental cell?
How many cells are produced at the end of the overall process?
In what cells of the body do they happen? What name do these
cells receive?
Are they diploid or haploid?
If the organism has a total of 46 chromosomes in body
cells, how many are present in the daughter cells?
How many sets of chromosomes are present in each
daughter cell?
Is genetic variability produced by means of this process?
2. Using a somatic (diploid) human cell as a starting point for meiosis, and keeping in mind that each
chromosome/chromatin molecule is composed of 1 DNA molecule if unduplicated and two if duplicated,
explain…
a) How many total chromosomes and DNA molecules would be present in G1 before Meiosis 1
b) How many total chromosomes and DNA molecules would be present in G2 before Meiosis 1
c) How many total chromosomes and DNA molecules would be present in daughter cells after Meiosis 1
d) How many total chromosomes and DNA molecules would be present in G1 before Meiosis 2
e) How many total chromosomes and DNA molecules would be present in G2 before Meiosis 2
f) How many total chromosomes and DNA molecules would be present in daughter cells after Meiosis 2
3. When do cells first become haploid (N)?
4. In what stages of meiosis is genetic variability produced and how? Explain each one of them (crossing over and
independent assortment)
5. a) For crossing over, in the exercise we did in the lab what genes were involved in the simulation?
b) What gene did cross over?
c) What was the result when it came to the number of different sex cells produced?
6. For independent assortment, use the example given in the lab exercise with 6 chromosomes in a diploid cell
(chromosome 1=long, chromosome 2=medium, chromosome 3=short), and show how you could get a sex cell
in which you would have mother #1, mother #2, father #3.
7. In what stage of meiosis 1 or 2 do homologous (mother and father) chromosomes separate?
8. In what stage of meiosis 1 or 2 do sister chromatids from each chromosome separate?
9. a) Explain what happens during the process called “meiotic non-disjunction”
b) In what stage of meiosis will non-disjunction take place?
c) How many cells are defective as a result of non-disjunction in meiosis 1? How many if in meiosis 2?
Instructor: Jose Bava, Ph.D