To Understand this, we most remember what the DNA is.
DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria (where it is called mitochondrial DNA or mtDNA).
The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism, similar to the way in which letters of the alphabet appear in a certain order to form words and sentences.The 22 autosomes are numbered by size. The other two chromosomes, X and Y, are the sex chromosomes.
DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.
An important property of DNA is that it can replicate, or make copies of itself. Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell.
In the nucleus of each cell, the DNA molecule is packaged into thread-like structures called chromosomes. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure.
Chromosomes are not visible in the cell’s nucleus—not even under a microscope—when the cell is not dividing. However, the DNA that makes up chromosomes becomes more tightly packed during cell division and is then visible under a microscope.
Each chromosome has a constriction point called the centromere, which divides the chromosome into two sections, or “arms.” The short arm of the chromosome is labeled the “p arm.” The long arm of the chromosome is labeled the “q arm.” The location of the centromere on each chromosome gives the chromosome its characteristic shape, and can be used to help describe the location of specific genes.
In humans, each cell normally contains 23 pairs of chromosomes, for a total of 46. Twenty-two of these pairs, called autosomes, look the same in both males and females. The 23rd pair, the sex chromosomes, differ between males and females. Females have two copies of the X chromosome, while males have one X and one Y chromosome.
Now moving on with the diferences between cat and dog's chromosome vs humans, first of all we find that the number is different.
Dogs have 39 pairs of chromosomes, for a total of 78. This works out to 76 autosomes and two sex chromosomes. As with other mammals, the karyotype of male dogs is XY whereas females' karyotype is XX
Although dogs have 39 pairs of chromosomes (compared to 23 pairs for humans), dogs have fewer genes overall. Researchers sequencing the canine genome have identified around 19,000 dog genes compared to the 25,000 or more genes in the human genome. Despite having 6,000 fewer genes than humans, dogs exhibit a diverse range of phenotypes, from animals as large as a Great Dane or St. Bernard to toy dogs weighing no more than a few pounds. Geneticists think the canine genome may be especially prone to gene duplications and chromosomal rearrangements compared to the genomes of humans and other mammals.
Most cats, including domestic breeds, have 19 pairs of chromosomes for a total of 38. Some types of cat in South America, however, have only 36 chromosomes, including ocelots, kotkots and margays. Dogs have more than double the number of chromosomes with 39 pairs.
Hopefully this information is somewhat useful, or at least fills in the curiosity of some of us.
MVZ Carolina Pruneda
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