Gene B alleles: dark blue/light blue (dark blue is dominant to light blue)
Genotype: Your organism is heterozygous for gene A and heterozygous for gene B. Assume the maternal copy of chromosome 1 has dominant alleles for both genes.
ii. On chromosome 2 reside genes C and D.
Gene C alleles: green/yellow (alleles have codominant relationship)
Gene D: Red (This gene is monomorphic: it only comes in one form!)
Genotype: Your organism is heterozygous for gene C, homozygous for gene D.
iii. On chromosome 3 resides gene E
Gene E alleles: pink/purple (Pink is dominant to purple)
Genotype: Your organism is homozygous for the recessive allele
5. As a group, count the number of chromosomes present in the hypothetical cell.
6. Form alignment along the metaphase plate. How are the replicated chromosomes (sister chromatids) aligned?
7. The 2 students role playing centrosomes will “rope” the sister chromatids and pull them apart to opposite poles of the
8. As a group, count how many chromosomes are present in the daughter cells.
End Mitosis role playing
B. Meiosis Modeling
1. Before you begin modeling, consider a diploid organism that has four chromosomes, numbered 1, 2, 3, 4. What is a
normal karyotype for a somatic cell of this organism?
2. “Replicate” your DNA chromosome by pulling the hidden sock out and then hold both socks in the same hand. Pins
with colored beads will be used to represent alleles. (This will be the same as above, you do not need to pin again)
3. Pairs of homologous chromosomes will need to form a tetrad (or bivalent) to participate in crossing over (also known
as homologous recombination). Students holding replicated chromosome 1s will indicate the formation of a bivalent by
4. Perform crossing over for one of the genes on chromosomes 1 and 2.
5. Are there any new allele combinations present after recombination that were not present before recombination?
6. What does alignment look like for metaphase of meiosis I?
7. Complete meiosis I by having student centrosomes separate bivalents (paternal and maternal homologous chromosomes) to 2 daughter cells.
8. As a group, count the number of chromosomes present in the hypothetical cell.
9. Complete meiosis II by having student centrosomes separate sister chromatids to daughter cells.
10. As a group, count the number of chromosomes present in the hypothetical cell.
End Meiosis role playing
Modeling Mitosis and Meiosis
A. Modeling Karyotypes and Genotypes
1. Consider a diploid organism that has four chromosomes, numbered 1, 2, 3, 4. What is a normal karyotype for a somatic
cell of this organism? To begin, model a normal karyotype of a somatic cell with the appropriate pipe cleaners.
2. Placing genes on chromosomes: