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Homologous and Non Homologous Chromosomes

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Last updated date: 23rd Apr 2024
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An Introduction to Chromosomes: Explaining Homologous and Non Homologous Chromosomes

In order to understand the difference between homologous and non homologous chromosomes, one must be aware of chromosomes, their structure, and function. 


Meaning of Chromosomes

Chromosomes hold the genetic material present in every cell. They are located in the nucleus of eukaryotic cells. They are structured similarly to threads. DNA and associated proteins called histones make up chromosomes in eukaryotic cells. They are in charge of the character traits that are handed on from parents to children from one generation to the next. DNA encodes for certain proteins and is the source of differences within and between different types of animals. Chroma means color and soma means body, and scientists have given these structures the name chromosomes because they are colored.


Structure of Chromosomes

The structure of chromosomes is quite intricate. The structure's foundation is made up of DNA, or deoxyribonucleic acid. Two chains of nucleic acid base pairs make up DNA. Cytosine, adenine, thymine, and guanine are the base pairs found in DNA. Due to the complementary pairing between each base and its counterpart on the opposing strand, the two strings of DNA create a spiral shape. Guanine pairs with cytosine, whereas adenine pairs with thymine. The strands are kept together by the formation of a phosphate-deoxyribose backbone on the bases' opposing sides.


Function of Chromosomes

In addition to the genetic code, the chromosome also contains a large number of the proteins necessary for its expression. How frequently genes may be translated into proteins and which genes are translated are determined by their intricate shape and structure. Gene expression is the process that results in the development of living things. How frequently a gene is expressed depends on how tightly packed the chromosome is at a specific place.

What is Homologous and Non Homologous Chromosomes?

Homologous Chromosomes: 

Two DNA molecules called homologous chromosomes, one from each parent, carry the same genes in a diploid creature. Both of your parents contribute to the whole genome. The identical 23 chromosomes from each parent contain identical genes. In total, our cells have 46 chromosomes in two copies. However, each gene may have a distinct variant on each homologous chromosome. More variation is produced, the negative impacts of mutations are diminished, and populations are typically stabilized when each gene has two copies.


Functions of Homologous Chromosomes:

In the process of creating gametes, homologous chromosomes participate in homologous recombination. Because of the exchange of homologous chromosomal segments when they come into close contact, this process is sometimes referred to as "crossing over." The genes on the chromosomes are similar in length and size, and they are all present. Between chromosomes, these segments are simply transferrable.


Non Homologous Chromosomes: 

Chromosomes that do not come from the same pair are referred to as non-homologous chromosomes. In non-homologous chromosomes, the form of the chromosome, that is, the length of the arms and the location of the centromere, is generally different. Therefore, meiosis does not result in the pairing of non-homologous chromosomes. Only the homolog of a specific organism's chromosome pairs with other chromosomes. According to the Law of Segregation, homologous pairs of chromosomes in the nucleus separate from other chromosomes.


Functions of Non Homologous Chromosomes:

A complete set of genes is present in every cell because of homologous chromosomes. Contrarily, non-homologous chromosomes increase genetic variety by rearranging the order of the genes during meiosis. Therefore, non-homologous chromosomes are crucial to evolution.


Homologous and Non homologous Chromosomes Difference 

S.No

Category

Homologous

Non homologous

1

Definition

It is a set of chromosomes with identical gene structures.

The pair of chromosomes is not the same.

2

Structure

The centromere position is the same for both chromosome arms.

Chromosome arm lengths and centromeric location are variable. 

3

Allele Type

Alleles are identical genes found at the same locus.

Alleles come from various genes.

4

Function

Each chromosome in the pair of chromosomes made up of the paternal and maternal chromosomes is related to the other.

Different homologous pairings make up the chromosomes.

5

Pairing

The meiotic process I results in the pairing of homologous chromosomes.

In meiosis I, non-homologous chromosomal pairing does not occur.

6

Example

Examples of homologous chromosomes in humans are the 22 autosomal chromosomes. XX chromosomes are another example.

The X and Y chromosomes are two examples of non-homologous chromosomes.


Summary

There are two different kinds of chromosomes in the genome: homologous and non-homologous. In the meiotic process, homologous chromosomes pair. Alleles of the same genes located at the same loci on both chromosomes make up the homologous pair. However, non-homologous chromosomes include alleles from several genes. The connection of alleles is what distinguishes homologous and non-homologous chromosomes from one another.

FAQs on Homologous and Non Homologous Chromosomes

1. What are the characteristics of homologous chromosomes?

Chromosomes that are homologous share some characteristics. They display the same structural characteristics, such as centromere locations, banding patterns, and size of identical genes located at identical loci (alleles may vary, despite identical genes). Prior to reproduction, homologous chromosomes must be divided into gametes (by meiosis) to stop the doubling of chromosomal numbers with each generation. They are copies of the same chromosome received from each parent and hence show similarity in shape and size.

2. What are the characteristics of non homologous chromosomes?

Chromosomes that do not come from the same pair are referred to as non-homologous chromosomes. They include alleles from many gene families. In non-homologous chromosomes, the form of the chromosome, that is, the length of the arms and the location of the centromere, is generally different. Therefore, meiosis does not result in the pairing of non-homologous chromosomes. For instance, non-homologous XY pairing occurs in human males when the mother supplies the X chromosome but the father provides the Y chromosome.

3. Explain Homologous and Non Homologous Chromosomes.

In the nucleus, chromosomes are formed from the genetic material of a cell. Homologous and non-homologous chromosomes are the two categories of chromosomes distinguished based on the pairing pattern of chromosomes during metaphase 1 of meiosis. When two chromosomes are paired together, a chromosome is said to be homologous, whereas non-homologous chromosomes have different chromosomal pairings. Homologous and non-homologous chromosomes are distinguished primarily by the presence of alleles of the same gene type at the same loci in homologous chromosomes, whereas alleles of various gene types are found in non-homologous chromosomes.