How can you identify homologous chromosomes

This is a preview of subscription content, access via your institution. Rent this article via DeepDyve. You can also search for this author in PubMed Google Scholar. Reprints and Permissions. Sybenga, J. What makes homologous chromosomes find each other in meiosis?

A review and an hypothesis. Chromosoma , — Download citation. A proposal for possible mechanisms is presented. It includes transcription and repair factors acting on coding sequences as a preparatory step toward pairing, and the attachment of specific pairing proteins to these sequences.

Double-strand break formation is prepared but not immediately completed at the same sites. When this occurs, the process is called chromosomal translocation. It is a form of mutation that could lead to severe chromosomal aberrations. For the comparison between homologous chromosomes and heterologous chromosomes, see table below.

At meiosis, each of the homologous chromosomes is comprised of two identical chromatids joined together by a common kinetochore centromere. The identical chromatids are specifically called sister chromatids to distinguish them from the so-called non-sister chromatids.

Prior to cell divisions, the chromosomes in the nucleus appear as threadlike strands called chromatins. When a cell is fated to undergo mitosis or meiosis, they condense into thicker structures. By this time, the chromatin is referred to as a chromosome. After replicating, there would have been two DNA copies, each present in a strand called chromatid. The two chromatids joined by a common centromere are referred to as sister chromatids. The chromatids of the other member of a homologous pair are referred to as non-sister chromatids.

Explore more! The chromosomes of a eukaryotic cell are located in the nucleus. The chromosomes in the nucleus are of two sets. One set would come from the male gamete sperm cell and the other set, from the female gamete egg cell. Prior to fertilization , both gametes are haploid. When the sperm cell successfully fertilizes the egg cell the resulting zygote is a diploid, which means the union of the two haploid cells results in a single cell with two sets of chromosomes: one set that is maternally-derived and another set that is paternally-derived.

Each maternal chromosome has a corresponding paternal chromosome of the same gene sequence, gene loci, chromosomal length, and centromere location. The pair comes close to each other during meiosis so that they could exchange genes between sister and non-sister chromatids. Although both members of the homologous pair have similar genes and loci, they may differ in the alleles.

For example, both of them carry genes coding for the eye color trait. One has alleles for the brown-eye trait whereas the other, for the blue-eye trait. In this case, the alleles are different and the homologous chromosomes are described as heterozygous. On the contrary, when the alleles are the same e. The significance of alleles was demonstrated by Gregor Mendel through his pioneering works in genetics using garden peas. He was able to show that one of the alleles may be dominant over the other.

In this case, only one allele will be expressed. A trait demonstrating this pattern is referred to as Mendelian inheritance. Nevertheless, in humans, genetic expressions are not straightforward. Many of the human traits do not conform to the Mendelian pattern of inheritance. In this regard, they are referred to as non-Mendelian. Meiosis is a form of cell division wherein diploid organisms halve their number of chromosomes and homologous chromosomes pair up. In contrast, mitosis another form of cell division results in two daughter cells, each containing the same chromosomal number as the parent cell.

In meiosis, a diploid 2n cell will give rise to four haploid n cells. The cells that undergo meiosis are the gametes producing haploid sperm cell and egg cell. Haploidy is essential so that at fertilization the chromosomal number remains the same throughout generations. In order to achieve haploidy, the cell undergoes two consecutive nuclear divisions. They are referred to as meiosis I and meiosis II.

To prepare the cell to meiosis, one of the major preparatory steps is DNA replication. The chromosomes duplicate their DNA, particularly in the S phase of interphase.

At this point, each of the chromosomes will consist of two strands sister chromatids joined at the centromere. The pairing synapse of homologous chromosomes will occur at prophase I. DNA exchanges occur between homologous chromosomes via homologous recombination and crossover at chiasmata between non-sister chromatids.

Then, the homologous pairs line up at the metaphase plate.