Drosophila melanogaster Hybrid Dysgenesis

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Questions and Answers

What is the primary reason for the occurrence of hybrid dysgenesis in D.melanogaster offspring?

The absence of regulatory factors in the egg (correct)

The high rate of mutation in the M strain females

The presence of regulatory factors in the sperm

The presence of P elements in the M strain females

What is the effect of radiation, chemical mutagens, and hormones on transposable elements?

They suppress the movement of transposable elements

They have no effect on the movement of transposable elements

They delete the transposable elements from the genome

They stimulate the movement of transposable elements (correct)

What is the consequence of homologous recombination between transposable elements located at different positions in the genome?

Chromosome breakage

Chromosomal rearrangements (correct)

Mutation

Gene inactivation

What is the process by which exons are inserted into the coding sequence of a gene via transposable elements?

Exon shuffling Signup and view all the answers

What is the primary effect of transposable elements on chromosome structure?

Chromosomal rearrangements Signup and view all the answers

Why are lab stocks of D.melanogaster collected prior to 1950 the only strains without the P element?

Because the P element was not present in the natural population at that time Signup and view all the answers

What is the result of incorrect excision of transposable elements?

Mutation Signup and view all the answers

What is the reason for the high regulation of transposition in natural populations?

To prevent harmful outcomes Signup and view all the answers

What is the primary function of transposable elements in the genome?

To integrate small segments of DNA into new locations Signup and view all the answers

What did Barbara McClintock term the locations where transposable elements have been inserted into chromosomes?

Mutable sites Signup and view all the answers

What is the result of Ds transposing out of the C allele during kernel growth?

The C allele function is restored Signup and view all the answers

What is the significance of transposable elements in terms of evolutionary significance?

They introduce genetic variation Signup and view all the answers

What is the term used to describe the process of transposable elements integrating into new locations in the genome?

Transposition Signup and view all the answers

What is the effect of a transposable element inserting into a gene?

The gene is inactivated Signup and view all the answers

What is the advantage of having multiple types of transposable elements in a genome?

It provides a source of genetic variation Signup and view all the answers

What is the term used to describe the result of a transposable element inserting into a gene, causing a change in kernel color?

Phenotypic variation Signup and view all the answers

What is the typical length of LINEs in eukaryotic genomes?

1,000 to 10,000 bp Signup and view all the answers

What percentage of the human genome is composed of LINEs?

Almost 17% Signup and view all the answers

Which of the following is an example of exon shuffling?

Insertion of exons into coding sequences Signup and view all the answers

What is the selfish DNA theory?

The idea that TEs exist because they can proliferate within the host without harming it Signup and view all the answers

What is a characteristic of SINEs?

They are less than 500 bp in length Signup and view all the answers

What is an example of a TE that carries antibiotic-resistance genes?

Bacterial TE Signup and view all the answers

What is the name of the TE that was introduced into Drosophila melanogaster in the 1950s?

P element Signup and view all the answers

What is a potential consequence of TEs causing greater genetic variability through recombination?

Evolution of genes with more diverse functions Signup and view all the answers

Study Notes

Hybrid Dysgenesis

Crossing D.melanogaster M strain females with P strain males produces offspring with abnormalities, including a high rate of mutation and chromosome breakage
This phenomenon is called hybrid dysgenesis and occurs because P elements can transpose freely in the egg, leading to harmful outcomes

Biological Significance of Transposons

Transposable elements have a variety of effects on chromosome structure and gene expression, mostly harmful
Transposition is usually highly-regulated and occurs only in a few individuals under certain conditions
Agents such as radiation, chemical mutagens, and hormones can stimulate the movement of transposons

Consequences of Transposition

Chromosome breakage can occur due to excision of a transposable element
Chromosomal rearrangements can occur due to homologous recombination between transposons at different positions in the genome
Mutation can occur due to incorrect excision of transposons
Gene inactivation can occur due to insertion of a transposon into a gene
Alteration in gene regulation can occur due to transposition of a gene next to regulatory sequences or the transposition of regulatory sequences next to a gene
Alteration in the exon content of a gene can occur due to insertion of exons into the coding sequence of a gene via transposons (exon shuffling)

Transposition

Transposition involves the integration of small segments of DNA into a new location in the genome
These small, mobile DNA segments are termed transposable elements (TEs) or "jumping genes"
TEs were first identified by Barbara McClintock in the early 1950s in corn

McClintock Discovers Moving Loci in Corn

McClintock identified many unusual features of corn chromosomes, including chromosomal breakage at a specific site (mutable locus)
The mutable locus was named Ds (dissociation) and was found to be a location where transposable elements had been inserted into the chromosomes
McClintock proposed that the colorless background of a kernel was due to the transposition of Ds into the C allele, inactivating it, and that the red sectors were due to the occasional transposition out of the C allele during kernel growth

Repetitive Sequences in Eukaryotic Genomes

Some repetitive sequences in eukaryotic genomes are due to the proliferation of transposons
Examples include LINEs (Long interspersed elements) and SINEs (Short interspersed elements) in mammals
LINEs are usually 1,000 to 10,000 bp long and occur in 20,000 to 1,000,000 copies per genome (almost 17% of the human genome)
SINEs are less than 500 bp in length and occur in about 1,000,000 copies in the human genome (10% of the genome)

Biological Significance of Transposons 2

Two schools of thought on the biological significance of transposons in evolution:
- Selfish DNA theory: TEs exist because they can proliferate within the host without harming it
- TEs exist because they offer some advantage, such as carrying antibiotic-resistance genes or causing greater genetic variability through recombination
Transposons may cause the insertion of exons into the coding sequences of protein-encoding genes, leading to the evolution of genes with more diverse functions (exon shuffling)

Biological Significance of Transposons 3

Transposable elements can rapidly enter the genome of an organism and proliferate quickly
Example: The P element was introduced into Drosophila melanogaster in the 1950s and has since expanded throughout the species

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Description

Learn about hybrid dysgenesis in Drosophila melanogaster, a phenomenon that occurs when crossing M strain females with P strain males, resulting in offspring with abnormalities.