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Homologous chromosome

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noun, plural: homologous chromosomes

(genetics) One of a pair of chromosomes with the same gene sequence


The chromosomes of may be divided into two sets: one that is derived from the mother and the other from the father. Each chromosome from the maternal set has a pair with that from the paternal set. The maternal chromosome that has the same gene sequence as the paternal chromosome pair up during meiosis and the pair is called homologous chromosomes. A homologous chromosome, therefore, would be one of the paired chromosomes that are homologous. In humans, the nucleus typically contains 46 chromosomes and they pair up during meiosis. Thus, there are 22 pairs of homologous non-sex chromosomes (or autosomes). The last one pair is the two sex chromosomes, (i.e. in females, the sex chromosomes are 2 X’s and in males, X and Y chromosomes).

The pairing of chromosomes during meiosis is called synapsis. It happens between chromosomes that are homologous, i.e. chromosomes having the same genes at the same loci but possibly different alleles. For example, two chromosomes have genes coding for eye color: one may code for brown eyes, the other for blue. One of them may be dominant and the other recessive. Hence, even if an individual has genes for brown eyes and blue eyes, only one eye color is expressed. This pattern of inheritance wherein the trait that is expressed follows the Mendelian laws is referred to as Mendelian inheritance. There are instances wherein the traits expressed do not conform to these laws; they are referred to as non-Mendelian.

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