Haemophilia is an X-linked recessive disease which expresses its effect only when both the alleles carry the recessive gene that in homozygous condition.
In the given question, according to the standardized rules and symbols to study the pedigree of disease suggests that the affected person should be represented by the filled male and female boxes with dark color.
So, by looking at the pedigree, one can conclude that John is not affected by the disease and does not carry the alleles for the disease.
In the given pedigree John has an XH chromosome, which means that he has the dominant chromosome. As males have one X, they can either be affected or unaffected. So, in this case John could not be carrier. Also, the Dominant chromosome is fully functional and does not show the characters of the disease, so, John would be free of hemophilia.
According to Charles Darwin's theory of evolution by natural selection, organisms that possess heritable traits that enable them to better adapt to their environment compared with other members of their species will be more likely to survive, reproduce, and pass more of their genes on to the next generation.
