Question

9-6 M. A. Merritt, 2016 1511 Lab Exercise #9 PROCEDURE 2: Simulation of the stages of Meiosis 1) To simulate synapsis, take the two homologous pairs of lona chromosomos and place one on top of the other. Do the same with the #2, medium length chromosomes and then the # 3 , short chromosomes., Fill in the sketch for PROPHASE 1 below, illustrating synapsis. Even though crossing over occurs in nature, DO NOT add CROSSING OVER to your sketch. After you complete the first sketch, continue with the rest, being sure to follow the descriptions of each phase on pages 9-4-9-5 of this exercise. Be sure to use 2 different colors of pen or pencil, (one for each color of pipe cleaner, which represents each set of chromosomes). Also be sure to sketch the 3 different lengths of pipe cleaners (i.e. chromosomes). Lastly, number each chromosome. PROPHASE 1 ANAPHASE 1 METAPHASE 1 Telo phase TELOPHASE 1 POST-CYTOKINESIS 1 PROPHASE 2 1 cell a nuclei T M. A. Merritt, 2016 1511 Lab Exercise #9 9-7 METAPHASE 2 ANAPHASE 2 6 T. TELOPHSE 2 TELOPHASE 2 POST-CYTOKINESIS 2 Have your instructor verify your sketches above, then fill in the chart below. If you have trouble eting the chart, examine the sketches. MEIOSIS: PROPHASE 1 How many total chromosomes are in the cell? Are the chromosomes unreplicated or diads? How many total DNA molecules per cell? Are sister chromatids present? Are sister chromatids still attached? How many total centromeres are there? How many homologous pairs of chromosomes? unreplicated XYES diads YES 3 Reproduction of Lab Exercise # 9 requires the author's written consent. NNO M. A. Merritt, 2016 1511 Lab Exercise #9 INTERPHASE G2 KYASON 7) When your sketch above is complete, answer the four questions directly below. KEEP THE PIPE CLEANERS AS IS, you will use them again. How many DNA double helices now make up one replicated, DIAD chromosome? How many sister chromatids are in one replicated, DIAD, chromosome? wemere nWhat is the name for the region on the replicaed chromosome where the sister chromatids are attached to each other? NO yes or no. Has the number of homologous pairs of chromosomes changed since the DNA replicated? ApnDmahd s shLanadud Ask your instructor to VERIFY your sketch above and answers on this page before continuing. IMEIOSIS Meiosis has two main stages, or cycles. Both stages (cycles) of Meiosis include a "Prophase, Metaphase, Anaphase and Telophase. Cytokinesis also occurs twice in Meiosis. Read the following descriptions of the stages of Meiosis, then work on "Procedure 2" During Prophase 1 of Meiosis 1, homologous pairs of chromosomes come together and intertwine. This intertwining of the homologous pairs of chromosomes, i.e. those with the same I.D. number and same genes, is called synapsis. Synapsis is an essential part of Meiosis, which does NOT occur in Mitosis. Synapsis attempts to ensure that the process of "crossing over", where homologous pairs of chromosomes physically exchange sections of DNA with each other, only should occur between homologous pairs of chromosomes. When sections of DNA are exchanged, ideally different versions (alleles) of the same genes are "traded". Crossing over provides the opportunity for a tremendous source of genetic variation in the daughter cells of Meiosis Examine the sketch on the top of the next page, which illustrates this concept M. A. Merritt, 2016 1511 Lab Exercise #9 lue le 2 2 seb 2ees An Homplogous Pair of Chromosomes BEFORE "Crossing Over ReD B lu RED leys 2 l les 4legsAn Homologous Pair of Chromosomes AFTER "Crossing Over In Metaphase 1, homologous pairs of chromosomes line up across the equator from each other, i.e. on opposite sides of the equator. This is quite different from Mitsosis, where all the chromosomes lined up, "single file", on the cell's equator. Like Mitosis, the color of the chromosomes and numerical sequence from left to right is random. In Anaphase1, homologous pairs of chromosomes are separated from each other as spindle fibers attach to their centromeres and pull them toward opposite poles of the cell. Whatever chromosomes were "above" the equator are pulled to the upper "north pole" of the cell, those that were below the equator to the opposite pole. This is very different from Mitosis, where sister chromatids are pulled apart during Anaphase. (n Telophase 1, the chromosomes at both ends, (poles) of the cell are packaged into-their own nuclei. This is similar to Mitosis, except in Meiosis the chromosomes are still replicated, and in Mitosis they are not. The other major difference between Telophase of Mitosis and Telophase 1 of Meiosis, is that in Mitosis the new nuclei are both diploid, in Meiosis they are haploid. ww. Telophase 1 is followed by cytokinesis one. The completion of the first stage, (i.e.cycle), of "Meios is I", results in the reduction of the number of chromosomes from the two sets found in the original, primary sex cell to one set in each of the 2 new daughter cells. This 50% reduction of chromosomes and DNA molecu les in each new daughter cell was accomplished by the separation of homologous pairs of chromosomes during Anaphase 1. For the remainder of Meiosis, all cells will be haploid, i.e. the homologous pairs are in separate cells, so each cell only contains one of each type of chromosome. The second stage, (i.e.cycle), of "Meiosis I", is where the remaining replicated chromosomes, each comprised of two attached sister chromatids, become unreplicated, each one another and pulled toward opposite ends of the cell. These "daughter chromosomes" will eventually be packaged into their own nuclei and cells. Meiosis II is much more similar to Mitosis than Meiosis I is. Hopefully, the terminology will become more familiar as you work with the pipe cleaners and concepts in this lab exercise. Just keep in mind, the goal of Meiosis is to make HAPLOID egg and sperm cells, so that each egg cell and sperm cell only has half of the "normal" number of chromosomes you would find in all other cells of the body. as each of the sister chromatids are detached from

Answer 1

nuclear membrane (X- cell membrane equatorial plate metaphase 1 (2n 4) prophase 1 (2n 4)

spindle fibers anaphase 1 (2n=4)

(XX)XX telophase 1 (2n=4)

XX XX X X post cytokinesis 1 each cell is n=2 prophase 2 n 2

metaphase 2 n-2

spindle fibers anaphase n 2

telophase 2 n 2+2

post cytokinesis 2 n-2

Prophase 1

There are 4 chromosomes. They are replicated and are called diads (each chromosome has 4 chromatids). So total there are 16 chromatids. There are 4 diads.

One diad is equal to 2 DNA molecules. So, there are 8 DNA molecules.

Homologous chromosomes are present in tetrads. Each replicated chromosome of a tetrad is a diad (one tetrad has 2 diads). So, they have sister chromatids. And they are attached to each other by centromere.

There are 4 centromeres. Each diad has one centromere.

There are 4 homologous pairs of chromosomes.

A PAIR OF diad HOMOLOGOUS CHROMOSOMES sister chromatids centromere non sister chromatids tetrad

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