Chromosomal Rearrangements: Deletions: Videos & Practice Problems

Deletions are chromosomal rearrangements resulting in the loss of chromosome segments, typically requiring double-stranded breaks. Types include enterogenic, multigenic, terminal, and intercalary deletions. A key phenotype is pseudodominance, where a recessive allele expresses its phenotype due to the absence of a dominant allele. Deletion loops facilitate proper segregation during meiosis. An example is Cri du Chat syndrome, caused by a deletion on chromosome 5, leading to a distinctive cat-like cry in affected infants. Understanding deletions is crucial for genetics and medical applications.

Deletions

Deletions are a significant type of chromosomal rearrangement characterized by the loss of a segment of a chromosome. This process typically involves double-stranded breaks, requiring two breaks to excise the segment. The deleted portion usually lacks a centromere, leading to its degradation during cell division, as it cannot attach to the spindle fibers responsible for segregating chromosomes into daughter cells.

There are various types of deletions, including:

• Gene Deletion: This type obliterates a single gene, rendering it nonfunctional.
• Multigenic Deletion: Involves the loss of multiple genes, significantly impacting genetic function.
• Terminal Deletion: This deletion occurs at the end of a chromosome.
• Intercalary Deletion: This type removes a segment from within the chromosome.

One notable consequence of deletions is a phenomenon known as Pseudodominance. This occurs when a dominant allele is deleted, leaving a recessive allele unopposed. For instance, if one chromosome carries a dominant allele and the other a recessive allele, the deletion of the dominant allele results in the expression of the recessive phenotype, which would typically remain masked.

To facilitate proper segregation during meiosis, a structure called a deletion loop forms between the normal homologous chromosome and the one with the missing segment. This loop allows for the alignment and segregation of chromosomes, ensuring that genetic material is accurately distributed to daughter cells.

An example of a deletion in humans is Cri du Chat Syndrome, which results from a deletion on chromosome 5. This syndrome is named for the distinctive cry of affected infants, which resembles a cat's meow, highlighting the real-world implications of chromosomal deletions.

An intragenic deletion is a deletion found where?

• A. In a centromere
• B. In a gene
• C. In multiple chromosomes
• D. In multiple genes

Answer: (B)

Deletions can cause what type of phenotype?

• A. Leaky allele
• B. Psudodominance
• C. Intercalary
• D. Faulty

Answer: (B)

Which of the following genetic diseases is an example of a chromosomal deletion?

• A. Down syndrome
• B. Familial down syndrome
• C. Cri du Chat syndrome
• D. Klinefelter's Disease

Answer: (C)

Here’s what students ask on this topic:

What are chromosomal deletions and how do they occur?

Chromosomal deletions are a type of chromosomal rearrangement that results in the loss of a segment of a chromosome. They typically occur due to double-stranded breaks in the DNA, which cut out a segment of the chromosome. The deleted segment usually lacks a centromere, causing it to be lost during cell division as it cannot attach to the spindle fibers. This loss can lead to various genetic disorders and phenotypic changes, depending on the genes located within the deleted segment.

What are the different types of chromosomal deletions?

There are several types of chromosomal deletions, including:

• Enterogenic Deletions: These occur within a single gene, often rendering the gene nonfunctional.
• Multigenic Deletions: These involve the loss of multiple genes, which can have more severe effects.
• Terminal Deletions: These involve the loss of the end of a chromosome.
• Intercalary Deletions: These occur within the interior of a chromosome, removing a segment between two breaks.

What is pseudodominance and how is it related to chromosomal deletions?

Pseudodominance is a phenomenon where a recessive allele expresses its phenotype due to the absence of a dominant allele. This occurs when a chromosomal deletion removes the dominant allele, leaving only the recessive allele. For example, if a dominant allele (A) and a recessive allele (a) are present, the dominant phenotype (A) will be expressed. However, if the segment containing the dominant allele (A) is deleted, only the recessive allele (a) remains, and its phenotype will be expressed.

What is a deletion loop and what role does it play in meiosis?

A deletion loop is a structure that forms during meiosis between a normal homologous chromosome and its partner containing a deletion. This loop allows for proper alignment and segregation of chromosomes during meiosis. The loop forms because the segment of the chromosome that is missing in one homolog cannot pair with the corresponding segment in the other homolog, causing the remaining segments to loop out. This ensures that the chromosomes segregate correctly, despite the deletion.

What is Cri du Chat syndrome and how is it related to chromosomal deletions?

Cri du Chat syndrome is a genetic disorder caused by a deletion on the short arm of chromosome 5. The name of the syndrome, which means 'cry of the cat' in French, comes from the characteristic cat-like cry of affected infants. This cry is due to abnormalities in the larynx and nervous system. The deletion leads to various developmental issues, including intellectual disability, delayed development, and distinctive facial features. Understanding this syndrome helps illustrate the significant impact that chromosomal deletions can have on human health.