What are homologous chromosomes? Every living cell, be it an animal, plant, or bacterial cell, has genetic material (DNA) packed into a circular structure called a chromosome.
While they are known to be located in the nucleus, chromosomes are only visible when cells are undergoing division. Most of what is found is by studying chromosomes during this process.
But have you ever heard of “homologous chromosomes”, or confused by the term? Here find out what these homologous chromosomes are, how they behave during different stages of cell division and cell cycle.
Homologous Chromosomes Definition
Homologous chromosomes are chromosomal pairs derived from each parent. In terms of structure, they have the same length and number of genes, ribbon patterns, gene location, as well as centromere location.
Although similar in most aspects, they come from different alleles; means genes may or may not be an alternative form of each other.
Basically, diploid organisms, like humans, have two pairs of homologous chromosomes inherited from mother and father.
Etymology of homologous chromosomes
The term homolog comes from the Greek homologos, meaning “agree” or “one mind”. It is a combination of homose**xual, which means “same” and logo, which means “relationship”. The term chromosome was coined in 1889 by the German anatomist Wilhelm von Waldeyer-Hartz. It comes from the Greek khrōma, which means “color” because it is easily colored with a base dye. Synonym: homologue.
Homologous Chromosome Pair
Humans have 46 chromosomes arranged in pairs (23 pairs) starting from the longest chromosome. Chromosomal pairs of the same length, centromere position, and coloring pattern are called homologue chromosomes (Greek; homo means like: and logous means proportional).
Both chromosomes of each pair carry the same gene, except for the somatic cells X and Y called se**x chromosomes. The se**x chromosome determines the se**x of the individual in which the female has a pair of X homologue chromosomes (XX) while the male has an X chromosome and a Y chromosome (XY).
Homologous chromosomes store the same gene sequences of a living being. Each part of the homologue chromosome pair comes from the chromosomes of the mother and father.
In humans themselves, spe**rm and the ovum each contain 23 chromosomes. Interactions occur during meiosis. Homologous chromosomes of two gamete cells line up and synapse (paired) and the parts can be swapped during recombination.
Homologous Chromosomes Function
Diploid organisms, like humans, carry two copies of the genome in each of their cells. It has two copies of each chromosome, called a homologous chromosome that function helps improve the variation and stability of a species. While each homologous chromosome carries the same gene, they can carry different versions of the gene. Different gene versions are called alleles.
This means that your cells will usually produce 2 versions of each protein encoded by the DNA. Some versions will work better than others. Furthermore, the combination of good and bad proteins produces different phenotypic effects that increase variation in a population. Some alleles have a dominant / recessive relationship, where the dominant gene is the only one that shows. Others have more complex relationships, and different allele combinations can produce very different effects on an organism.
This is important because variation helps populations survive in the face of environmental changes.
The next function of homologue chromosomes is homologous recombination during gamete formation. This process is also known as “”crossing over”, as parts of homologue chromosomes are exchanged when they occur in close contact. Chromosomes contain the same genes, which generally have the same length and size. These parts can be easily transferred between chromosomes.
Homologous Chromosomes Characteristics
Eukaryotic cell chromosomes are located in the nucleus. The chromosomes in the nucleus consist of two sets. One set will come from a male gamete (spe**rm cell) and another set, from a female gamete (egg cell).
Before conception, both gametes were haploid. When spe**rm cells successfully fertilize an egg, the resulting zygote is a diploid, which means the unification of two haploid cells produces one cell with two sets of chromosomes: a set that is maternally inherited and a set that is paternally derived.
Each maternal chromosome has a corresponding paternal chromosome of the same gene sequence, gene locus, chromosomal length, and centromere location. The pair approach each other during meiosis so they can exchange genes between chromatic sisters and non sisters.
Although both members of the homologous pair have similar genes and locus, they may differ in the alleles. For example, both carry genes that encode the color properties of the eye. One has alleles for eye-brown properties, while the other for blue-eye properties. In this case, the alleles are different and its homologue chromosomes are described as heterozygous.
Conversely, when the alleles are the same (e.g. Both alleles to the same genetic code for blue-eye properties), they are said to be homozygous. The significance of the alleles was demonstrated by Gregor Mendel through his pioneering work in genetics using peas.
He was able to show that one allele may be dominant above the other. In this case, only one allele will be expressed. A trait that indicates this pattern is referred to as Mendel heritage.
However, in humans, genetic expression is indirect. Many human traits do not conform to Mendel’s devolution pattern. In this case, they are referred to as non-Mendel.
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- Video: MooMooMath and Science