Final answer:
The expected ratio of surviving offspring from a cross between an achondroplastic dwarf and a person of normal height is 2:1, reflecting one normal height to one dwarf, as homozygous recessive offspring are non-viable due to the dominant lethal inheritance pattern.
Step-by-step explanation:
Achondroplasia, a form of dwarfism in humans, follows a pattern of dominant lethal inheritance. This means that individuals who are homozygous for the allele associated with achondroplasia do not survive. In a cross between an achondroplastic dwarf (heterozygous for the allele) and an individual of normal height with no achondroplasia allele, the potential offspring can inherit three genotypes: normal height (homozygous dominant), dwarfism (heterozygous), and the lethal homozygous recessive genotype.
However, individuals with the lethal homozygous recessive genotype do not survive, leading to a specific pattern of inheritance. The surviving offspring will have either the normal height genotype or the dwarfism genotype. The expected ratio of surviving offspring is 2:1, consisting of one normal height individual to one dwarf.
This pattern emerges because the heterozygous achondroplastic dwarf parent can pass on either the dominant normal height allele or the recessive achondroplasia allele to their offspring. The individual of normal height only contributes the dominant normal height allele. As a result, only the offspring inheriting at least one normal height allele (either homozygous dominant or heterozygous) or the heterozygous achondroplastic dwarf allele will survive, leading to the 2:1 ratio of viable offspring with normal height to dwarfism in this particular cross.