Why are Great Danes so much larger than Chihuahuas

1
Why are Great Danes so much larger than
Chihuahuas?
IGF1 (encoding insulin-like growth factor 1)
partially explains why
2
Fig. 1. Relationships of skeletal size, SNP
markers, IGF1 haplotype, and serum levels of the
IGF1 protein in PWDs

• Probability that
• specific SNPs are
• associated with
• size phenotype
• in Portugese
• Water dogs (PWD)

B/B

• B. Frequency
• of IGF1
• Genotypes in
• PWDs

I/I
C. Serum IGF1 phenotypes of B/B, B/I, and
I/I PWDs.
B/I heterozygotes are the dashed line
N. B. Sutter et al., Science 316, 112 -115
(2007)
Published by AAAS
3
Fig. 2. Signatures of recent selection on the
IGF1 locus across 22 small and giant dog breeds

• Ratio of small breed
• heterozygotes to large
• breed heterozygotes.

B. Genetic differentiation between small and
large breeds.
Small breeds
Large breeds
N. B. Sutter et al., Science 316, 112 -115
(2007)
C. SNP heterozygosity along chromosome 15.
Published by AAAS
4
Fig. 4. Association of body size and frequency of
the SNP 5 A allele
Frequency of a specific SNP allele In various
breeds
N. B. Sutter et al., Science 316, 112 -115
(2007)
Published by AAAS