Question

To simulate Prophase of Meiosis I - Synapsis and Crossing Over:

1. Homologous chromosomes come together and synapse along their entire length. This pairing (synapsis) of homologous chromosomes represents the first big difference between mitosis and meiosis. This pairing will produce two tetrads, each consisting of four chromatids. Entwine the two chromosomes to simulate synapsis.

2. To simulate crossing over, start with your long tetrad and transfer the circles on the red chromatid at the fourth bead or “gene” to the yellow chromatid, and the yellow circles to the red chromatid. Now take your short tetrad and transfer your circles from the red chromatid at the second bead or “gene” to the yellow chromatid and the yellow circles to the red. Proceed through meiosis and note how crossing over results in recombination of genetic information.

3. Draw your two centrioles to opposite poles (sides) of the cell and be sure not to draw the nuclear membrane.

4. Draw the arrangement of your tetrads and provide a brief description of what happens during

prophase of meiosis I.

Answer 1

Ans1)

A couple of homologous chromosomes, or homologs, are a set of one maternal and one paternal chromosome that pair up with each other inside a cell during fertilization. Homologs have the same genes in the same loci where they provide points along each chromosome which enable a pair of chromosomes to align correctly with each other before separating during meiosis.This is the basis for Mendelian inheritance which characterizes inheritance patterns of genetic material from an organism to its offspring parent developmental cell at the given time and area.

Homologous chromosomes are chromosomes which contain the same genes in the same order along their chromosomal arms. There are two main properties of homologous chromosomes: the length of chromosomal arms and the placement of the centromere.

The actual length of the arm, in accordance with the gene locations, is critically important for proper alignment. Centromere placement can be characterized by four main arrangements, consisting of being either metacentric, submetacentric, acrocentric, or telocentric. Both of these properties are the main factors for creating structural homology between chromosomes. Therefore, when two chromosomes of the exact structure exist, they are able to pair together to form homologous chromosomes.

Since homologous chromosomes are not identical and do not originate from the same organism, they are different from sister chromatids. Sister chromatids result after DNA replication has occurred, and thus are identical, side-by-side duplicates of each other.

Ans2)

Ans 3)

Ans 4)

Meiosis 1 separates the pair of homologous chromosomes and reduces the diploid cell to haploid. It is divided into several stages that include, prophase, metaphase, anaphase and telophase.