Question

Achondroplasia, a form of dwarfism, is inherited as a dominant condition. Two dwarfs, both of whom had one parent of normal height, marry and plan to a have child. Their first child is born and is a dwarf. What is the probability that they will have more dwarf children

Answer 1

Two dwarfs, both heterozygous for achondroplasia, have a 75% chance of having a dwarf child due to the dominant inheritance pattern. The fact that their first child is a dwarf does not affect the probability for future offspring.

Step-by-step explanation:

Achondroplasia is a form of dwarfism inherited as a dominant condition. When considering two dwarfs who each have one parent of normal height, we can deduce that each dwarf must be heterozygous for the achondroplasia gene (Dd), where 'D' represents the dominant allele for dwarfism and 'd' the normal allele. The probability of them having a dwarf child is calculated using a Punnett square which predicts that the genotypes of the offspring could be DD (homozygous dominant), Dd (heterozygous), or dd (homozygous recessive).

Since DD individuals would likely not survive or are extremely rare due to the lethal nature of the homozygous dominant combination, the realistic genotypes for surviving offspring are Dd or dd. For each child born to this couple, there is a 75% chance of inheriting the dominant allele for dwarfism (D from either parent) and a 25% chance of being of normal height (dd).

The fact that their first child is a dwarf (most likely Dd) does not affect the probability of future offspring being dwarfs. It remains a 75% probability for each subsequent child.