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Genes and Chromosomes

Topic Review on "Title":

Genes control the genetic traits, and genes are DNA, which is organized into chromosomes.  Both prokaryotes and eukaryotes have chromosomes, although the organization level is different.  A gene is a region of DNA segment that controls certain trait of inheritance, while chromosome is the basic inheritance unit in cells.  Genes are arranged on chromosomes linearly. 

Prokaryotic chromosome
Prokaryotes do not have nucleus but they have their own chromosomes, which contain either linear or circular DNA molecules.  DNA is naked in prokaryotes, which means they do not associate with histones.  Prokaryotes usually only have one copy of chromosome, therefore they are haploid.  Virus and organelles in an eukaryotes also have chromosomes similar to chromosomes in prokaryotes.

Eukaryotes chromosome
Eukaryotes usually have large, linear and multiple chromosomes within a cell nucleus.  DNA forms highly packed structure and wrapped with histones.  These chromosomes are visible under light microscope when a cell is in metaphase of mitosis.

Genome organization in eukaryotes
Genes are arranged linearly on chromosomes.  Usually a gene has a regulatory region which is called promoter and a coding sequence which determines the amino acid sequence of the gene.  For majority of the genes in mammalian cells, the coding sequence is interrupted by non-coding sequence called introns (the coding sequence are called exons).

One-gene-one-protein hypothesis
Proposed by Beadle and Tatum in 1942, this hypothesis linked the enzyme function to genes.  Based on the hypothesis, a mutation outcome can be predicted if genes are within a biochemical pathway.

Rapid Study Kit for "Title":
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Core Concept Tutorial Problem Solving Drill Review Cheat Sheet

"Title" Tutorial Summary :

Genes are functional segments of DNA, which is highly organized and packed into nucleosomes and then chromosomes in eukaryotes, existing on two homologous chromosomes (two copies).  While in prokaryotes genes are “naked” and single copy.  Genes are arranged linearly on chromosomes, with a promoter, exons and introns.  One-gene-one-protein hypothesis provided a link between a mutation and an enzyme to explain the observed phenotype in a biochemical pathway.

Tutorial Features:
  • External concept map to describe the relationship of genes and chromosome and other disciplines in biology
  • Internal concept map to reveal the relationships among the content within this tutorial
  • Side by side comparison of prokaryotic and eukaryotic chromosomes
  • Color diagram and scheme to describe DNA packing into eukaryotic chromosomes
  • Step by step deduction of one-gene-one-protein hypothesis
  • Color table listing some genetic disease and the mutated genes that caused these diseases.

"Title" Topic List:


  • Genes
  • Chromosomes

Prokaryotic chromosomes

  • Bacterial chromosomes
  • Viral and phage chromosomes
  • Organelle chromosomes

Eukaryotic chromosomes

  • The Karyotype and Chromosome Banding
  • Organization of DNA into Chromosome
  • Nucleosomes
  • Organization of Genome

One-gene-one-protein hypothesis

  • One-gene-one-enzyme Hypothesis
  • Enzyme deficient and genetic disease
  • Genetic Counseling

See all 24 lessons in college biology, including concept tutorials, problem drills and cheat sheets:
Teach Yourself Genetics Visually in 24 Hours

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