Transposable Genetic Elements - Genetics | BIO 328, Study notes of Genetics

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Chapter 17

Transposable Genetic Elements

Chapter Outline

• Transposable Elements: An Overview
• Transposable Elements in Bacteria
• Cut-and-Paste Transposons in Eukaryotes
• Retroviruses and Retrotransposons
• Transposable Elements in Humans
• The Genetic and Evolutionary Significance of

Transposable Elements

Types of Transposition

• Cut-and-Paste transposition
  • An element is cut out of one site in a chromosome and pasted into a new site
• Replicative transposition
  • An element is replicated, and one copy is inserted at a new site
• Retrotransposition
  • An element is transcribed and the RNA is used as a template to synthesize DNA molecules, which are then inserted into new chromosomal sites

Ac and Ds Elements in Maize

• Discovered by Barbara McClintock
• Aleurone color is affected by the Cl^ allele, which encodes dominant inhibitor of aleurone coloration.
• Mosaics with pigmented patches were caused by loss of the Cl^ allele.

Activities of the Ac/Ds Elements

• The Ac element encodes a transposase that is responsible for excision, transposition, mutation, and chromosome breakage.
• The Ac transposase interacts with sequences at the ends of Ac and Ds elements and catalyzes their movement.
• Deletions or mutations in the Ac gene abolish its catalytic function.

The Structure of P Elements

© John Wiley & Sons, Inc.

© John Wiley & Sons, Inc.

The Life

Cycle of HIV

Replication of the HIV Genome

Integration of the HIV Double-Stranded DNA

into Chromosomal DNA

Retroviruslike Elements

• Found in yeast, plants, and animals.
• Structure: central coding region flanked by long

terminal repeats (LTRs) oriented in the same direction.

• The coding region contains homologues of the

gag and pol genes of retroviruses.

Retroposons (non-LTR Retrotransposons)

• Retrotransposons are a large and widely distributed class of retrotransposons.
• Retroposons move through an RNA molecule that is reverse transcribed into DNA.
• Retroposons have a homologous sequence of A:T base pairs at one end that is derived from the poly(A) tail of retroposon RNA.

TRANSPOSABLE ELEMENTS

IN HUMANS

The human genome is populated by a diverse array of transposable elements that collectively account for 44 percent of all human DNA.