How Many Chromosomes Do Dogs Have? 78, Explained

Dogs have 78 chromosomes in each body cell, arranged in 39 pairs. Thirty-eight of those pairs are autosomes, the chromosomes males and females share. The last pair is the sex chromosomes: two X chromosomes in a female, or an X and a Y in a male. Egg and sperm cells carry half the set, 39 chromosomes each.

The short version

• 78 chromosomes in each body cell, in 39 pairs.
• 38 pairs of autosomes, numbered by size and shape, with the largest called chromosome 1.
• One pair of sex chromosomes: XX in females, XY in males.
• 39 in each egg or sperm cell, so a puppy gets half its chromosomes from each parent.
• People have 46, so chromosome number isn't a measure of how complex an animal is.

What a chromosome is

A chromosome is a long strand of DNA, tightly packed around proteins, that carries many genes in a fixed order. Each gene sits at its own position, called a locus, and the version of the gene a dog carries there is called an allele. Because chromosomes come in pairs, a dog has two copies of most genes, one on each chromosome of the pair.

How dogs compare with people

According to the American Kennel Club's genetics guide for breeders, the dog genome is organized into 78 chromosomes in each body cell and 39 in egg and sperm cells, made up of 38 pairs of autosomes plus the sex chromosomes.

More chromosomes doesn't mean more genetic complexity. The number reflects how each species' DNA happens to be packaged.

How a puppy inherits its chromosomes

Each egg and sperm cell carries one chromosome from each pair, 39 in all. When they combine, the puppy has a full set of 78: half from its mother and half from its father. Which copy of each pair a parent passes on is down to chance, which is one reason littermates can look so different. Our guide to dominant vs recessive genes shows how that plays out for a single gene.

The sex chromosomes decide whether a puppy is male or female. Every egg carries an X chromosome, and each sperm carries either an X or a Y, so the sperm that fertilizes the egg determines the puppy's sex.

Chromosomes and dog traits

Each gene sits at a fixed place on a chromosome. A 2007 study of body size, for example, found a region on chromosome 15 with a major influence on size and traced it to a single gene, IGF1. Our guide to whether DNA can predict adult size explains what that gene does, and our glossary explains the other terms you'll meet in a DNA report.