What makes chromosomes homologous

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. Next, the homologous chromosomes separate during anaphase I and move to the opposite poles of the cell. Then, the cell divides for the first time during telophase I resulting in two genetically non-identical daughter cells but with sister chromatids still intact.

Each cell will undergo meiosis II so that the resulting daughter cells will each have a chromosomal number reduced by half. In humans, the nucleus typically contains 46 chromosomes.

Thus, there are 22 pairs of autosomes with approximately the same length, staining pattern, and genes with the same loci. As for the sex chromosomes, the two X chromosomes are considered as homologous whereas the X and Y chromosomes are not. Thus, females have 23 homologous chromosomes i. They also bear the genetic information that determines the trait of an organism. Homologous chromosomes, therefore, are vital in the same way. They carry genetic information that has been passed down from one generation to the next.

And since alleles may possibly be different in the same gene, the result is varying phenotypes. Thus, the distinctiveness of an individual of the same species is established.

Apart from this, the organism is capable of reproducing offspring that is genetically different from itself as well as from the rest of its descendants. This event is crucial to promote genetic variation.

The homologous pair exchanges genes via genetic recombination so that genetic diversity may be promoted. This is regarded as one of the advantages of having been able to reproduce sexually. Those that reproduce asexually create a clone of themselves. Thus, this could reduce the gene pool.

A small gene pool means low genetic diversity. It could be unfavorable because it means there is less opportunity in acquiring genes essential for adapting to an environment prone to inexorable physicochemical changes.

In contrast, greater genetic variability means a higher propensity to acquire better genes. High genetic diversity also means a large gene pool. This, in turn, implicates increased chances of acquiring genes that could enhance biological fitness and survival. Got questions on homologous chromosomes? Our community may be able to help! Mutations can also influence the phenotype of an organism. This tutorial looks at the effects of chromosomal mutations, such as nondisjunction, deletion, and duplication.

Read More. Plants are characterized by having alternation of generations in their life cycles. This tutorial is a review of plant mitosis, meiosis, and alternation of generations. This tutorial looks at sex determination via the sex chromosomes, X and Y. Read it to get more info on X and Y chromosomes and the genetic traits inherited via these two This tutorial describes the independent assortment of chromosomes and crossing over as important events in meiosis.

Read this tutorial to know more details in each of these meiotic events and how they promote genetic diversity in sexually-reproducing organisms Humans are diploid creatures.

This means that for every chromosome in the body, there is another one to match it. 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. Chromosoma , — Download citation.

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