Homologous chromosomes

A couple of homologous chromosomes, or homologs, are a set of one maternal and one paternal chromosomes that pair up with each other inside a cell during meiosis. These copies have the same genes in the same loci where they provide points along each chromosome which enable a pair of chromosomes to align correctly with each other before separating during meiosis. This is the basis for Mendelian inheritance which characterizes inheritance patterns of genetic material from an organism to its offspring parent developmental cell at the given time and area.

Chromosomes are linear arrangements of condensed deoxyribonucleic acid (DNA) and histone proteins, which form a complex called chromatin. Homologous chromosomes are made up of chromosome pairs of approximately the same length, centromere position, and staining pattern, for genes with the same corresponding loci. One homologous chromosome is inherited from the organism's mother; the other is inherited from the organism's father. After mitosis occurs within the daughter cells, they have the correct number of genes which are a mix of the two parents' genes. In diploid (2n) organisms, the genome is composed of one set of each homologous chromosome pair, as compared to tetraploid organisms which may have two sets of each homologous chromosome pair. The alleles on the homologous chromosomes may be different, resulting in different phenotypes of the same genes. This mixing of maternal and paternal traits is enhanced by crossing over during meiosis, wherein lengths of chromosomal arms and the DNA they contain within a homologous chromosome pair are exchanged with one another.

Early in the 1900s William Bateson and Reginald Punnett were studying genetic inheritance and they noted that some combinations of alleles appeared more frequently than others. That data and information was further explored by Thomas Morgan. Using test cross experiments, he revealed that, for a single parent, the alleles of genes near to one another along the length of the chromosome move together. Using this logic he concluded that the two genes he was studying were located on homologous chromosomes. Later on during the 1930s Harriet Creighton and were studying meiosis in corn cells and examining gene loci on corn chromosomes. Creighton and McClintock discovered that the new allele combinations present in the offspring and the event of crossing over were directly related. This proved intrachromosomal genetic recombination.

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