gene

Examples of gene in the following topics:

• Epistasis

  • The B gene controls black (B_) vs. brown (bb) color, while the E gene controls yellow (ee) color.
  • Genes may also oppose each other with one gene modifying the expression of another.
  • Often the biochemical basis of epistasis is a gene pathway in which the expression of one gene is dependent on the function of a gene that precedes or follows it in the pathway.
  • In this case, the C gene is epistatic to the A gene.
  • Thus, the C gene is epistatic to the A gene.

• Altered Gene Expression in Cancer

  • Cancer, a disease of altered gene expression, is the result of gene mutations or dramatic changes in gene regulation.
  • Cancer can be described as a disease of altered gene expression.
  • There are many proteins that are turned on or off (gene activation or gene silencing) that dramatically alter the overall activity of the cell.
  • This can be the result of gene mutation or changes in gene regulation (epigenetic, transcription, post-transcription, translation, or post-translation).
  • It can bind to sites in the promoters of genes to initiate transcription.

• Epigenetic Alterations in Cancer

  • Silencing genes through epigenetic mechanisms is very common in cancer cells and include modifications to histone proteins and DNA that are associated with silenced genes.
  • When these modifications occur, the gene present in that chromosomal region is silenced.
  • In cancer cells, silencing genes through epigenetic mechanisms is a common occurrence.
  • Mechanisms can include modifications to histone proteins and DNA associated with these silencing genes.
  • Describe the role played by epigenetic alterations to gene expression in the development of cancer

• Gene Duplications and Divergence

  • Gene duplication is the process by which a region of DNA coding for a gene is copied.
  • Duplicate genes are often immune to the selective pressure under which genes normally exist.
  • Many retrogenes display changes in gene regulation in comparison to their parental gene sequences, which sometimes results in novel functions.
  • This can apply to genes and proteins, such as nucleotide sequences or protein sequences that are derived from two or more homologous genes.
  • Both orthologous genes (resulting from a speciation event) and paralogous genes (resulting from gene duplication within a population) can be said to display divergent evolution.

• Variations in Size and Number of Genes

  • Nucleotide variation is measured for discrete sections of the chromosomes, called genes.
  • In humans, more proteins are encoded per gene than in other species.
  • M.leprae has lost many once-functional genes over time due to the formation of pseudogenes.
  • The repeat-rich regions contain genes coding for host interaction proteins.
  • This figure represents the human genome, categorized by function of each gene product, given both as number of genes and as percentage of all genes.

• The Relationship Between Genes and Proteins

  • Proteins, encoded by individual genes, orchestrate nearly every function of the cell.
  • Genes are composed of DNA and are linearly arranged on chromosomes.
  • Some genes encode structural and regulatory RNAs.
  • Protein-encoding genes specify the sequences of amino acids, which are the building blocks of proteins .
  • Both protein-encoding genes and the proteins that are their gene products are absolutely essential to life as we know it.

• Genes as the Unit of Heredity

  • Genes exist in pairs within an organism, with one of each pair inherited from each parent.
  • A gene has a certain influence on how the cell works; the same gene in many different cells determines a certain physical or biochemical feature of the whole body (e.g., eye color or reproductive functions).
  • All human cells hold approximately 21,000 different genes.
  • Homologous chromosomes have the same genes in the same positions, but may have different alleles (varieties) of those genes.
  • Describe the structure of a gene and how offspring inherit genes from each parent

• Prokaryotic versus Eukaryotic Gene Expression

  • Prokaryotes regulate gene expression by controlling the amount of transcription, whereas eukaryotic control is much more complex.
  • To understand how gene expression is regulated, we must first understand how a gene codes for a functional protein in a cell.
  • Therefore, in prokaryotic cells, the control of gene expression is mostly at the transcriptional level.
  • The regulation of gene expression can occur at all stages of the process .
  • Eukaryotic gene expression is regulated during transcription and RNA processing, which take place in the nucleus, and during protein translation, which takes place in the cytoplasm.

• Horizontal Gene Transfer

  • Conjugation: the use a hollow tube called a pilus to transfer genes between organisms.
  • More recently, a fourth mechanism of gene transfer between prokaryotes has been discovered.
  • Transposons or "jumping genes" have been shown to transfer between rice and millet plant species.
  • Genes necessary to make this pigment are present in certain fungi.
  • Explain how horizontal gene transfer can make resolution of phylogenies difficult

• The Process and Purpose of Gene Expression Regulation

  • At any given time, only a subset of all of the genes encoded by our DNA are expressed and translated into proteins.
  • The expression of specific genes is a highly-regulated process with many levels and stages of control.
  • In this section, you will learn about the various methods of gene regulation and the mechanisms used to control gene expression, such as: epigenetic, transcriptional, post-transcriptional, translational, and post-translational controls in eukaryotic gene expression, and transcriptional control in prokaryotic gene expression.
  • The genetic content of each somatic cell in an organism is the same, but not all genes are expressed in every cell.
  • The control of which genes are expressed dictates whether a cell is (a) an eye cell or (b) a liver cell.