17 Questions
Which molecular method can be used to detect higher gene dosage as a consequence of duplications?
Southern blotting
What is a common evolutionary consequence of gene duplications?
Neofunctionalization
In terms of phenotype, how can gene dosage affect protein synthesis?
It is often proportional to the number of gene copies present
Which region in Drosophila exhibits an effect on the number of eye facets due to gene duplication?
Bar region
What type of genes do duplications create, leading to the formation of multigene families?
Gene families
What can be detected during meiosis using a variety of molecular methods?
Deletion loops
What is the consequence of a deletion that spans a centromere?
Formation of an acentric chromosome
What is the term used when deletions allow the expression of alleles that are normally recessive?
Pseudodominance
Which genetic disorder emphasizes the importance of gene dosage?
Cri du chat syndrome
What is the primary consequence of tandem duplications?
No impact on phenotype/viability
What can result from unbalanced 'dosage' of gene products due to duplications?
Problems due to excess protein dosage
What is one of the consequences of acentric chromatid loss in chromosomal rearrangements?
Reduced (observed) recombination frequency
Which type of chromosomal rearrangement involves the exchange of segments between nonhomologous chromosomes?
Translocation
In a reciprocal translocation, what might be the result of genes changing positions?
Formation of new gene products
What is a balanced translocation?
Translocation where no genetic material is lost
Which type of chromosomal rearrangement involves the fusion of segments between two different chromosomes?
Translocation
How do inversions and translocations differ in their effects on gene expression?
Both inversions and translocations alter gene expression.
Study Notes
Deletions
- Deletions can be detected during meiosis or by molecular methods that detect lower heterozygosity or gene dosage.
- Loss of DNA sequences can result in phenotypic effects, depending on the size and location of deleted sequences.
- Deletions that span a centromere result in an acentric chromosome, which can be lethal.
- Deletions can allow expression of alleles that are normally recessive, known as pseudodominance.
- Deletions can affect gene dosage, leading to haploinsufficiency if one copy of a gene is deleted.
Duplications
- Duplications are the repetition of a chromosome segment, which can occur in tandem.
- Duplications can have little or no effect on phenotype and viability if small.
- However, excess or unbalanced gene dosage from duplications can cause problems.
- Duplications are important in evolution, providing raw material for new genes and adaptations.
- About 5% of the human genome consists of duplications.
Origins and Detection of Duplications
- Unequal crossing over of misaligned chromosomes during meiosis generates duplications.
- Duplications can be detected by molecular methods that detect higher gene dosage.
Evolutionary Consequences of Duplications
- Duplication can result in redundancy, alteration of gene dosage, or neofunctionalization.
- One copy of a duplicated gene can become inactive, becoming a pseudogene.
- One copy can acquire a new function, leading to the creation of multigene families (e.g., globin gene family).
- Extra gene copies can lead to excess proteins, affecting phenotype (e.g., Bar region in Drosophila).
Chromosomal Rearrangements
- There are four types of chromosomal rearrangements: deletions, duplications, translocations, and inversions.
Translocations
- Translocations involve the exchange of segments between nonhomologous chromosomes or to a different region on the same chromosome.
- Translocations can be reciprocal (two-way) or non-reciprocal (one-way).
- Balanced translocations do not result in genetic material loss.
- Translocations can change gene expression or form new gene products (fusion proteins).
Explore the significance of gene duplications in evolution, with a focus on how extra copies of genes can lead to the creation of new genes and adaptations. Learn about the detection and origins of gene duplications through molecular methods and unequal crossing over during meiosis.
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