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Homologous chromosomes

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Definition

noun, singular: homologous chromosome

(genetics) A pair of chromosomes having the same gene sequences, each derived from one parent


Supplement

In a cell, the chromosomes are of two sets: one of which is derived from the mother and the other is from the father. The chromosomes that have the same gene sequences are paired during meiosis. This pairing (called synapsis) 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.

In humans, the nucleus typically contains 46 chromosomes. 22 of them are homologous non-sex chromosomes (or autosomes). The last pair is the two sex chromosomes; in females, the sex chromosomes are 2 X’s and in males, X and Y chromosomes.


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