Topic 3.2:  Chromosomes

Essential Idea:  Chromosomes carry genes in a linear sequence that is shared by members of a species.
At SHS, Topic 3.2 is taught in the following class unit(s):

Statements & Objectives:

3.2.U1  Prokaryotes have one chromosome consisting of a circular DNA molecule.
  • Describe the arrangement of prokaryotic DNA (nucleoid and plasmid).
  • Define the term “naked” in relation to prokaryotic DNA.​
3.2.U2  Some prokaryotes also have plasmids but eukaryotes do not.
  • Describe the structure and function of plasmid DNA.​
3.2.U3  Eukaryote chromosomes are linear DNA molecules associated with histone proteins.
  • Describe the structure of eukaryotic DNA and associated histone proteins during interphase (chromatin).
  • Explain why chromatin DNA in interphase is said to look like “beads on a string.”
3.2.U4  In a eukaryote species there are different chromosomes that carry different genes.
  • List three ways in which the types of chromosomes within a single cell are different.
  • State the number of nuclear chromosome types in a human cell.​
3.2.U5  Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes.
  • Define homologous chromosome.
  • State a similarity and a difference found between pairs of homologous chromosomes.
3.2.U6  Diploid nuclei have pairs of homologous chromosomes.
  • Define diploid.
  • State the human cell diploid number.
  • Outline the formation of a diploid cell from two haploid gametes.
  • State an advantage of being diploid.​
3.2.U7  Haploid nuclei have one chromosomes of each pair.
  • Define haploid.
  • State the human cell haploid number.
  • List example haploid cells.​
3.2.U8  The number of chromosomes is a characteristic feature of member of a species.
  • State that chromosome number and type is a distinguishing characteristic of a species.
  • List mechanisms by which a species chromosome number can change.​
3.2.U9  A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length.
  • Describe the process of creating a karyogram.
  • List the characteristics by which chromosomes are arranged on the karyogram.​
3.2.U10  Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex.
  • Outline the structure and function of the two human sex chromosomes.
  • Outline sex determination by sex chromosomes.
3.2.A1  Cairns’ technique for measuring the length of DNA by autoradiography.
  • Describe Cairn’s technique for producing images of DNA molecules from E. coli.
  • Outline conclusions drawn from the images produced using Cairn’s autoradiography technique.  ​​
3.2.A2  Comparison of genome size in T2 phage, Escherichia coli, Drosophila melanogaster, Homo sapiens, Paris japonica.
  • Describe the relationship between the genome size of a species and the species complexity in structure, physiology and behavior.​
3.2.A3  Comparison of diploid chromosome numbers of Homo sapiens, Pan troglodytes, Canis familiaris, Oryza sativa, Parascarsis equorum.
  • State the minimum chromosome number in eukaryotes.
  • Explain why the typical number of chromosomes in a species is always an even number.
  • Explain why the chromosome number of a species does not indicate the number of genes in the species.
  • Explain the relationship between the number of human and chimpanzee chromosomes.​
3.2.A4  Use karyograms to deduce sex and diagnose Down Syndrome in humans.
  • Distinguish between a karyogram and a karyotype.
  • Deduce the sex of an individual given a karyogram.
  • Describe the use of a karyogram to diagnose Down syndrome.  
3.2.S1  Use of databases to identify the focus of a human gene and its polypeptide product.
  • Search NCBI or OMIM for a given gene.
  • Determine the gene locus, abbreviated gene name, and description of the gene.​
3.2.NOS  Developments in research follow improvements in techniques- autoradiography was used to establish the length of DNA molecules in chromosomes.
  • Outline the advancement in knowledge gained from the development of autoradiography techniques.​
"When we try to pick out anything by itself, we find it hitched to everything else in the Universe." 
 John Muir,   1911