The key difference between autosomes and chromosomes is that humans have 22 pairs of autosomes that determine somatic characteristics while humans have a total of 23 pairs of chromosomes in a cell.
As cell theory explains, a new cell originates from a pre-existing cell by cell division. Further studies have recognized the importance of the cell division and function of the chromosome. In eukaryotes, chromosomes are present in the nucleus while in prokaryotes, they are present in the cytoplasm. Chromosomes are visible only during the metaphase of the nuclear division. During the interphase of nuclear division, chromosomes appear as a bundle of strings called chromatin. There are two types of chromosomes in a cell: autosomes and sex-determining chromosomes. Females have sex a determining pair of chromosomes composed of XX while males have XY chromosomes. The y chromosome is shorter than the X chromosome and it lacks some gens that occur in the X chromosome.
CONTENTS
1. Overview and Key Difference
2. What are Autosomes
3. What are Chromosomes
4. Similarities Between Autosomes and Chromosomes
5. Side by Side Comparison – Autosomes vs Chromosomes in Tabular Form
6. Summary
What are Autosomes?
Autosomes are one of the two types of chromosomes present in humans. These chromosomes mainly determine the general characteristics of both female and male. Out of 23 pairs of chromosomes, 22 pairs of chromosomes are autosomes. The other pair is responsible for the gender of humans. Autosome pairs are different in sizes and shapes. But, two members of the autosomal chromosome pair have the same morphology, unlike the sex chromosome pair. In a karyotype, the arrangement of the autosome pairs reveals their sizes. Chromosome pair 1 is the largest autosome pair that contains a higher number of genes while pair 22 is the smallest autosome pair that contains a comparatively small number of genes.
Figure 01: Autosomes
There are several disorders associated with autosomes. Down syndrome is a disorder that occurs due to trisomy of chromosome pair 21 while Cri du Chat is an autosomal disorder that occurs due to the inheritance of just one copy of part of chromosome 5. Likewise, cystic fibrosis, sickle cell anaemia, Tay-Sachs disease, trisomy 13 and trisomy 18 are some more autosomal disorders.
What are Chromosomes?
Chromosomes are threadlike structures composed of DNA associated with histone proteins. Chromosomes carry genetic information of an organism. A chromosome has a centromere region and two sister chromatids. Centromere can be present anywhere along the length of the chromosome. In eukaryotes, chromosomes are present in the nucleus while in prokaryotes, they are present in the cytoplasm. Bacteria contain one chromosome in the cytoplasm, but bacteria have extra-chromosomal DNA called plasmids. Furthermore, bacterial chromosomes do not associate with histone proteins. Hence, they are naked DNA.
Figure 02: Chromosomes
Chromosomes are responsible for the transmission of the genetic information from one generation to another generation since they carry genes which are the units of inheritance. In fact, genes are the specific DNA sequences or fragments of chromosomes. In one chromosome, there may be several thousand genes, which are responsible for different characteristics.
Each species has a unique number of chromosomes in each cell. Humans have 46 chromosomes. Common fruit flies have 8 chromosomes. Cats have 38 while dogs have 78 chromosomes. In a cell, chromosomes exist as pairs. These chromosome pairs are identical. They are homologous chromosomes inherited from mother and father. So, a human has 23 homologous chromosome pairs: 22 pairs are autosomes while one pair is sex chromosomes.
What are the Similarities Between Autosomes and Chromosomes?
• Autosomes are chromosomes that determine the general characteristics of human.
• They are composed of DNA.
• They contain genes.
What is the Difference Between Autosomes and Chromosomes?
Autosomes are non-sex chromosomes while chromosomes are thread-like structures composed of DNA that carry genetic information of an organism. Therefore, this is the key difference between autosomes and chromosomes. Autosomes determine general characteristics of an organism while chromosomes collectively determine the overall characteristic of an organism, including the gender and sex-related characteristics. Another difference between autosomes and chromosomes is the total number of pairs. There are 22 pairs of autosomes while 23 pairs of chromosomes in a cell of humans. Moreover, all autosome pairs are homologous while sex chromosomes of males are not homologous.
Summary – Autosomes vs Chromosomes
Chromosomes represent the genome of an organism that carries genetic information. They are threadlike structures composed of nucleic acid DNA. In addition, there are two types of chromosomes as autosomes and allosomes (sex chromosomes). Autosomes contain genes that code for somatic characteristics. In contrast, sex chromosomes determine the gender of the organism. There are 44 autosomal chromosomes and 46 chromosomes in a cell of humans. This summarizes the difference between autosomes and chromosomes.
Reference:
1. “Autosome – Definition and Function of Autosomes.” Biology Dictionary, 28 Apr. 2017, Available here.
Image Courtesy:
1. “Chromosome karyotype” By Zappys Technology Solutions (CC BY 2.0) via Flickr
2. “NHGRI Fact Sheet- Chromosomes (26454931343)” By National Human Genome Research Institute (NHGRI) from Bethesda, MD, USA – (CC BY 2.0) via Commons Wikimedia