Difference between genes and chromosomes

One gen is a portion of deoxyribonucleic acid (DNA) that encodes a protein or RNA. One chromosome it is a nuclear structure that corresponds to the packaging of DNA where there are a number of genes. That is, the chromosome is a large portion of DNA, the molecule responsible for the genetic information of living things, expressed through genes.

Gen. Chromosome
Definition Functional unit of inheritance Linear structure of DNA packaging
Location On the chromosomes In the cell nucleus
Composition DNA Chromatin: DNA and proteins
Type

Nothing structural

No regulators

Nothing specialized

Nothing constitutive

Pseudogens

Depending on the function in the cell:

  • Somatic chromosomes or autosomes
  • X and Y sex chromosomes

Depending on the location of the centromere:

  • Metacentric chromosomes
  • Submetacentric chromosomes
  • Acrocentric chromosomes
  • Telocentric chromosomes
Examples

ACTB gene: the actin gene.

BRCA1 gene: tumor suppressor gene.

INS gene: insulin gene.

Human being (Homo sapiens): 46 chromosomes

Mouse (Mus musculus): 40 chromosomes

Gorilla (Gorilla gorilla): 48 chromosomes

What are genes?

Difference between chromosome and gene
Scheme of gene localization in DNA and chromosome in cell nucleus.

Genes are functional units of inheritance. A gene is defined as a segment of the DNA sequence corresponding to a protein, a set of protein variants or structural RNA molecules that do not produce proteins.

The Human Genome Project determined that the human beings have 20,000 to 25,000 genes in their genome to the 3 billion base pairs of DNA. The fruit fly Drosophila melanogaster it possesses approximately 14,000 genes in 137 million base pairs and the plant Arabidopsis thaliana owns approx. 26 thousand genes to 142 million base pairs of DNA.

Genes in eukaryotic cells have:

  • Promoter region: DNA sequence that precedes the sequence that encodes a protein. It is the region that controls gene transcription.
  • Coding region: DNA sequence transcribed into mRNA and then translated into an amino acid sequence.
  • Exons: DNA sequences that are presented in the final messenger RNA.
  • Introns: Intermediate sequences that are removed in the messenger RNA.

Types of genes

Genes can be of the following types:

  • Nothing structural: as the ACTB gene encoding the actin protein, important in the cytoskeleton of the cell.
  • No regulators: encode proteins that regulate the transcription of other genes.
  • Nothing specialized: genes that are only expressed in certain cells; for example, the globin gene in red blood cell precursor cells.
  • No maintenance or constituents (from English housekeeping gens): they are genes whose transcription is constant in the cell and that fulfill the basic functions of the same.
  • Pseudogens: they are non-functional genes, the result of the accumulation of mutations.

Function of genes

Genes are the elements that contain the information that determines the characteristics of species. They also control the development and functions of cells. For example, the BRCA1 gene on human chromosome 17 encodes a protein that maintains genome stability and acts as a tumor suppressor.

What are chromosomes?

human chromosomes
Normal human chromosomes.

Chromosomes are stranded structures that are located inside the nucleus, made up of DNA and proteins. The eukaryotic cells of each species of a living thing have a fixed and constant number of characteristic chromosomes. For example, the human being Homo sapiens it has 23 pairs of chromosomes or 46 chromosomes.

Chromosomes are visible under a microscope when cells begin to divide. In a given species, chromosomes can be identified by their number, size, centromere position, and band pattern. He karyotype is the number and appearance of human chromosomes.

In organisms where sexual reproduction exists, the sex cells or gametes possess half of the chromosomes of the species, that is, they are haploid. For example, in humans, eggs have 23 chromosomes and sperm also have 23 chromosomes.

The number of chromosomes is not related to the complexity of the organism. This is the case for human somatic cells, where there are 46 chromosomes, while in mice there are 42, and in cattle 60.

Chromosome structure

Each chromosome has:

  • a constipation that is called centromere;
  • end ends known as telomeres;
  • two arms, one small or arm p (for the French small) and a long o arm q.

Types of chromosomes

somatic and sex chromosomes
Scheme of somatic chromosomes and human sex chromosomes.

In living things where two sexes are differentiated, chromosomes are classified into:

  • Somatic chromosomes: are those chromosomes identical between individuals of a species, regardless of sex. In humans there are 22 pairs of somatic chromosomes, also called homologous chromosomes.
  • Sex chromosomes: are a pair of chromosomes that determine the sex of the individual. In humans, a pair of X (XX) chromosomes determines that the individual is female, while an X chromosome and a Y (XY) chromosome determine that the individual is male.

Additionally, chromosomes can be classified according to the position of the centromere at:

  • metacentric chromosomes: the centromere is in the middle of the chromosome;
  • submetacentric chromosomes: the centromere is located at one end;
  • acrocentric chromosomes: the centromere is very close to the end, which produces a very small p-arm;
  • telocentric chromosomes: the centromere is exactly at the end.

Function of chromosomes

The main function of chromosomes is DNA packaging inside the nucleus. Human DNA comprises more than 3 billion base pairs, which if spread could measure 2 meters, but the nucleus is barely 0.000006 meters long!

Chromosomal abnormalities

Chromosomal disorders where there is a change in the number of chromosomes in the species is known as aneuploidy, within which we have:

  • Trisomy: given by the presence of an extra chromosome in the cell. For example, Down syndrome or trisomy 21 is characterized by having three copies of chromosome 21, instead of the two normal copies.
  • Monosomy: given by the absence of a chromosome in the cell. For example, Turner syndrome, where there are only 45 chromosomes with a single X chromosome.

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Ana Zita Fernandes

PhD in Biochemistry from the Venezuelan Institute of Scientific Research (IVIC), with a degree in bioanalysis from the Central University of Venezuela.

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