Paired Chromosomes Of clean animals and of animals that are not clean.two and two, male and female, went into the ark with Noah as God had commanded Noah. Genesis 7:8-9 Introduction A chromosome is a DNA molecule a double-stranded polymer of nucleic acids residing in the nucleus of a cell. A gene is a section of the chromosome that codes for the making of a specific protein, and as such is the basic unit of heredity. The gene may be as small as a few hundred nucleic acids or as large as a few million nucleic acids. In humans, the chromosomes vary in length from long to very short. Depending upon the length of the chromosome, it may contain hundreds to thousands of genes. In fact, when a karyotype of a human s DNA is shown, the chromosomes are arranged from the longest (Chromosome 1) to the shortest (Chromosome 22) chromosomes. Chromosome 23 pair is shown last and is the pair that determines the sex of the individual. When the cell is not dividing the chromosomes are coiled around proteins called histones. When the cell is about to undergo division, the chromosome will be duplicated, and the chromosome will become even more tightly packed. The duplicated chromosome will not separate from its duplicated sister but will be bound to its sister chromatid by a large protein complex called the centromere. Body cells in a eukaryotic organism contains two copies of each chromosome one copy from the father and one from the mother. This double set of chromosomes is called the diploid (2n) number. In humans, the diploid number is 46. Mitosis is the division process by which a diploid (2n) parent cell divides to produce two daughter cells with the same number and the same kind of chromosomes. The process, mitosis, results in diploid (2n) cells and is typical of ordinary tissue growth. Meiosis, on the other hand, is cell division in which a diploid (2n) parent cell divides to produce four daughter cells with half the number of chromosomes called the haploid (n) number. In humans, the haploid number is 23. In this lab, you will be introduced to chromosomes and sister chromatids. In the next two labs, you will examine the two division processes of mitosis and meiosis more closely. Learning Objectives: Understand that chromosomes come in pairs Materials Required: From Biology Kit Chenille Stems (pipe cleaners) (4) Student Supplied Markers 2 different colors Ruler Safety The pipe cleaners are not toys, keep away from small children. 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 1
Definitions Definitions involved in meiosis: Allele Alternate forms of the same gene found at the same location on a homologous chromosome Chromatid One of two identical copies of chromosomes held together by a centromere, formed when a chromosome replicates itself during cell division. Also called sister chromatids Chromosome Highly condensed structure of DNA surrounded by proteins found when cells are undergoing division to ensure that genetic information is divided equally between the two resulting daughter cells Diploid Cells that have two copies of each chromosome, one from each parent (called 2n) Gamete A cell containing a haploid number of chromosomes Gene A DNA sequence on a chromosome coding for a specific protein Haploid Cells that have one copy of each chromosome (called n) Homologous Chromosomes One chromosome from each homologous pair comes from mother (maternal chromosome) and one comes from father (paternal chromosome). They are similar but not identical each have genes in same order but alleles for each trait may differ. Locus (loci, plural) The location of a specific gene on a chromosome. Alleles on homologous chromosomes have the same loci. Somatic Cells Diploid cells not involved in gamete formation Tetrad Four homologous chromosomes made up of two sister chromatids and formed during the prophase of meiosis Experiment Important Note: You will prepare 2 chromosomal sets which when put together represents the full set of DNA in the body (somatic) cells of the organism we will study today. The chromosomal sets are: (1) Maternal Set consisting of 3 chromosomes (long, medium, short) representing those chromosomes supplied by the organism s mother; (2) Paternal Set consisting of 3 chromosomes (long, medium, short) representing those chromosomes supplied by the organism s father. Preparation of Chromosomes 1. Prepare Maternal Chromosomal Set Chromosome 1 Take 2 pipe cleaners and color a portion of them with a marker (pink, for example) This color shall designate the chromosomes supplied to the organism from its mother On both chromosomes place two boxed marks representing Genes as described: o Gene A about 1-inch in length, placed about 1-inch from end o Gene B about ½-inch in length, placed about 4-inches from end Gene A represents a gene that codes for a specific protein Gene B represents a gene that codes for a different specific protein 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 2
Chromosome 2 Cut two, 8-inch pieces from a second and third pipe cleaner Mark them with the maternal (pink) color marker Chromosome 3 Take the two, 4-inch remainder of pipe cleaners Color a portion of them with maternal color 2. Prepare Paternal Chromosomal Set Chromosome 1 Take 2 pipe cleaner and color a portion of them with a marker (blue, for example) This color shall designate the chromosomes supplied to the organism from its father On these 2 chromosomes place two boxed marks representing Genes as described: o Gene A about 1-inch in length, placed about 1-inch from end o Gene B about ½-inch in length, placed about 4-inches from end Chromosome 2 Cut two 8-inch pieces from a second and third pipe cleaner Mark them with the paternal (blue) color marker Chromosome 3 Take the 4-inch remainders of pipe cleaners Color a portion of them with paternal color 3. Prepare Pre-Replication Chromosomal Set From the Maternal set, draw out 1-long, 1-medium, and 1-short chromosomes From the Paternal set, draw out 1-long, 1-medium, and 1-short chromosomes Combine these 6 chromosomes together o Set the other 6 aside for later analysis This combination represents the full complement of chromosomes in the organism prior to DNA replication Proceed on to the Analysis of Chromosomes Prior to Replication below Analysis of Chromosomes Prior to Replication 4. Using Table 1, answer the questions and observations Question A: Count the total number of chromosomes in the set Question B: Determine the diploid number for the organism Question C: Organize the chromosomes into pairs based on length Question D: What is different about the two chromosomes in each pair? What is the cause of their difference? Question E: What is the same in the two chromosomes in each pair? Question F: The paired chromosomes are called chromosomes. 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 3
5. Genes: (Use Table 1 to answer the questions and observations) Question G: Gene A on Chromosome 1 is the of Gene A on Chromosome 2 since they occur at the same and code for the same protein. Question H: Can there be differences between Gene A on Chromosome 1 and Gene A and Chromosome 2? Explain. Analysis of Chromosomes AFTER DNA Replication 6. In the S-phase of Interphase, the DNA replicates and the chromosomal number doubles Retrieve the second set of chromosomes, previously set aside Proceed on to the questions below 7. Using Table 2, answer the questions and observations Question I: Organize the chromosomes into pairs based on both length and color. How many pairs are there? Question J: Take each pair and connect them by wrapping one pipe cleaner around the other in one location. What is the name of the DNA region where the chromosomes join? Question K: What is each chromosome in a pair called? Question L: Diagram and label one of these pairs of connected chromosomes. Include all parts identified in Questions I-K Analysis of Mitosis and Meiosis The cell has duplicated the DNA during the S-phase of Interphase as a preparation to enter the cell division phase of mitosis in somatic cells, or the gamete-producing phase of meiosis in sex cells. Below, we will see why DNA replication is necessary, and how mitosis and meiosis differ. 8. Mitosis Arrange the chromosomes as they would appear during metaphase of mitosis. Question M: What structure attaches to the constricted part of the chromosomes? Question N: Diagram the arrangement of the chromosomes as you have arranged them. 9. Meiosis Arrange the chromosomes as they would appear during Metaphase I of meiosis. Question O: Diagram the arrangement of the chromosomes as you have arranged them. Question P: Compare and contrast the daughter cells at the end of mitosis with the daughter cells at the end of meiosis 10. Perform Data Analyses and Conclusions 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 4
Lab Report for: Question A. How many total chromosomes are in this cell? B. What is the diploid number of this cell? C. How many pairs are there in this cell? D. Explain the difference between the chromosomes in each pair. E. What is similar about the chromosomes in each pair? F. What are paired chromosomes called? G. Alternative forms of the same gene: Table 1 Set 1 Answer There are total chromosomes. Diploid number (2n) = There are pairs in each cell when matched by length. The chromosomes in each pair are called chromosomes. Gene A on Chromosome 1 is the of Gene A on Chromosome 2 since they occur at the same and code for the same protein. (See Figure in Lab Protocol) H. Can there be differences between Gene A on Chromosome 1 and Gene A and Chromosome 2? Explain 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 5
Question I. How many duplicated chromosome pairs? Table 2 Sets 1 and 2 Answer There are chromosome pairs when matched by length and color. J. What is the DNA region connecting the pairs (for example, the pair containing Chromosomes W and X)? K. What is each chromosome in a pair called? The is the constriction in the DNA which connects paired Chromosomes W and X, and paired Chromosomes Y and Z (See Figure in Lab Protocol). Chromosome W is the of Chromosome X; just as Chromosome Y is the of Chromosome Z (see figure in Lab Protocol). L. Diagram and label one of these pairs of chromosomes, including all terms identified in Questions I-K. [The WORD commands <insert> <shape> and <insert> <text> may be used if desired.] M. What structure attaches to the constricted portion of the chromosomes? N. Diagram the chromosomes as they would appear at Metaphase during mitosis in this organism. O. Diagram the chromosomes as they would appear at Metaphase I during meiosis in this organism. P. Compare and contrast the daughter cells at the end of mitosis with the daughter cells at the end of meiosis growing from the at either pole of the cell, attach to the centromere of each chromosome pair. In this cell there are (a number) daughter cells at the end of mitosis; there are (a number) daughter cells at the end of meiosis. After mitosis in this cell, each daughter cell contains chromosomes which is the (diploid/haploid) number After meiosis, each daughter cell contains chromosomes which is the (diploid/haploid) number. 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 6
Data Analyses and Conclusions 1. What is the purpose of mitosis? Of meiosis? 2. In the cell you modeled, what was the diploid number (2n) for the parent cell? What was the haploid number? 3. Why is DNA replication necessary prior to mitosis? 4. Why is it necessary to reduce the number of chromosomes in gametes but not in skin cells? 2016 Catholic Initiatives in Math and Science, LLC All Rights Reserved 7