Question

14. Anchondroplasia is a form of human dwarfism. If two individuals with achondroplasia have children with the following ratio, 2 dwarf to 1 wild type, what is the means of inheritance of this phenotype?

1. Simple dominance
2. Simple recessive
3. Dominant lethal
4. Recessive lethal
5. Epistasis

Answer 1

Answer: Option C- Dominant lethal.
Explanation: Achondroplasia is an autosomal dominant lethal disease. The genes can cause dwarfism in the case of heterozygous conditions. In homozygous dominant condition, it is lethal that the child may be stillborn or die shortly. Here, two heterozygous parents who are dwarf were mated and they will have children in the ratio 1:2:1 where 2 children will be heterozygous and dwarf. One will die soon after birth and one will be a wild type.

# Simple dominance: Dominance occurs when the two alleles controlling the gene expression are different and among them, one will dominate the expression of others. The expressing one will be dominant and the later is recessive.

# Simple recessive: The recessive allele is suppressed by the dominant allele in the heterozygous condition. Simple recessive is a condition where both the alleles are recessive and thus are homozygous. Thus they can express their allelic function.

# Recessive lethal: The homozygous condition of this dominant or recessive allele will cause death. In the heterozygous condition, they cannot show any diseased condition.

# Epistasis: In epistasis, one gene will suppress or mask the activity of another gene such that a character can be thus altered by the changes or mutation of several genes.