Translocation between the 2 acrocentric chromosomes with breakpoint occurring close to the centromeres, so that very large and very small chromosomes are obtained from which smaller fragment is usually lost. The type of cytogenic abnormality is:
**Core Concept**
Translocations involving acrocentric chromosomes with breakpoints near the centromeres result in the formation of two large and two small chromosomes, with the smaller fragments often being lost. This type of chromosomal abnormality is a specific type of translocation that occurs between the short arms of two acrocentric chromosomes.
**Why the Correct Answer is Right**
A Robertsonian translocation occurs when two acrocentric chromosomes share a segment, resulting in the formation of large and small chromosomes. The breakpoints occur near the centromeres, leading to the loss of the smaller fragment. This type of translocation is named after William R. Robertson, who first described it. The loss of the smaller fragment can lead to genetic imbalance and increased risk of genetic disorders.
**Why Each Wrong Option is Incorrect**
**Option A:** Deletion refers to the loss of a segment of DNA from a chromosome, which is different from the translocation of segments between two or more chromosomes.
**Option B:** Balanced translocation refers to a type of translocation where the segments exchanged between chromosomes are equal in size and the individual has no net loss or gain of genetic material. However, Robertsonian translocation involves the loss of the smaller fragment.
**Option D:** Inversion refers to a type of chromosomal rearrangement where a segment of DNA is reversed end to end within a chromosome, which is distinct from the translocation of segments between two or more chromosomes.
**Clinical Pearl / High-Yield Fact**
Robertsonian translocations are a common cause of chromosomal abnormalities and can lead to genetic disorders such as Down syndrome (trisomy 21) and Patau syndrome (trisomy 13). These translocations can also increase the risk of miscarriage and infertility.
**✓ Correct Answer: C. Robertsonian translocation**