Page 09 18. Ellis-van Creveld syndrome is a rare genetic condition. It is much more common in an isolated population in North America, which was founded by a small number of individuals, than in the general population. The most likely explanation for this is A natural selection B sexual selection C random mutation D genetic drift. 19. The frequency of a given allele in a population is a measure of how common that allele is as a proportion of the total number of copies of all alleles at a specific locus. For a locus with one dominant allele (A) and one recessive allele (a), the frequency of the dominant allele (p) and the frequency of the recessive allele (q) can be used to calculate the genetic variation of a population using the equations below. p + q = 1 p = frequency of A allele q = frequency of a allele p2 + 2pq + q2 = 1 p2 = frequency of homozygous (AA) individuals q2 = frequency of homozygous (aa) individuals 2pq = frequency of heterozygous (Aa) individuals If the allele frequency of the recessive allele is 0·7, the proportion of individuals that would be heterozygous is A 0·09 B 0·21 C 0·42 D 0·49. [Turn over