A cruciform structure of chromosomes during meiosis is a characteristic feature of:
Translocation
Cruciform Chromosome Structure Explained
During meiosis, the process where germ cells divide to produce gametes, chromosomes undergo precise pairing and recombination. Certain structural changes in chromosomes can lead to unusual pairing configurations.
A cruciform structure, which is cross-shaped, is a specific chromosomal configuration observed during the prophase I stage of meiosis.
Translocation and Cruciform Structure
Translocation is a type of chromosomal aberration where a segment of one chromosome breaks off and attaches to a non-homologous chromosome. In a reciprocal translocation, segments are exchanged between two non-homologous chromosomes.
Individuals who are heterozygous for a reciprocal translocation have one pair of normal chromosomes and one pair of chromosomes that have undergone translocation. During the pachytene stage of prophase I in meiosis, homologous regions of these four chromosomes (two normal, two translocated) attempt to pair up. This leads to the formation of a unique cross-shaped structure involving all four chromosomes.
The four arms of the cross correspond to the paired segments of the four chromosomes. This cruciform structure is a direct consequence of the specific pairing requirements of the translocated and normal chromosomes.
| Chromosomal Change | Typical Meiotic Pairing Structure |
|---|---|
| Translocation (heterozygous reciprocal) | Cruciform structure (involving 4 chromosomes) |
| Inversion | Inversion loop |
| Deletion | Loop in normal homolog |
| Duplication | Loop in chromosome with duplication |
Other Chromosomal Changes
While other chromosomal changes like Inversion, Deletion, and Duplication also affect chromosome pairing during meiosis, they result in different structures:
- Inversion: Leads to the formation of an inversion loop when homologous chromosomes pair.
- Deletion: The region on the normal homologous chromosome that corresponds to the deleted segment forms a loop because it has no partner on the other chromosome.
- Duplication: The duplicated segment forms a loop during pairing.
None of these typically produce the four-chromosome cross characteristic of a reciprocal translocation.
Meiosis and Translocation Pairing
The cruciform structure during meiosis is a key indicator of a reciprocal translocation in a heterozygous state. The way these four chromosomes align and segregate during later stages of meiosis (anaphase I) determines the viability of the resulting gametes, often leading to reduced fertility or the production of unbalanced gametes.
Therefore, the cruciform structure of chromosomes during meiosis is a characteristic feature specifically associated with Translocation.
Important Questions from Alterations of chromosomes
A species of plant (species 1) is diploid (2n = 6) with chromosomes AABBCC and a related species (species 2) is also diploid (2n = 4) with chromosomes PPQQ. The following statements were given by students regarding the chromosome numbers involving these plant species:
A. Autotriploid of species 1 will have 12 chromosomes
B. Allotetraploid involving species 1 and 2 will have 16 chromosomes
C. A monosomy in species 1 will generate 5 chromosomes
D. A double trisomy in species 1 will generate 8 chromosomes
E. A nullisomy in species 2 will generate 2 chromosomes
The combination of statements with all correct answers is:
Fertilization of gametes containing chromosome with duplications or deletions often results in children with disabilities. What is the probability of a couple where the male is karyotypically normal and the female has a pericentric inversion in heterozygous condition producing a child with disabilities if crossing over took place within the pericentric inversion in 26% of meiotic divisions?
In this case consider that fertilization with a gamete containing chromosomes with duplications or deletion will result in disabilities.
Chromosomal inversions are balanced rearrangements and thus do not change the overall amount of genetic material. While inversions can exist in homozygous condition, some only exist as heterozygotes. In the latter condition, the breakpoint disrupts:
A colour blind father has a daughter who is also colour blind and has Turner's syndrome. The genotype of the daughter is due to:
If a gamete produced following non disjunction of a chromosome at second meiotic division was fertilized by a normal gamete, what is the expected frequency of trisomic progeny?
