If parents are carrier for an autosomal recessive disorder. What are the chances of offspring to get affected-
**Core Concept:**
Autosomal Recessive Disorders: Inheritance pattern where the genetic mutation is located on an autosome (non-sex chromosomes) and requires the presence of two copies of the mutated gene (one from each parent) for the individual to exhibit the disease. Offspring from unaffected parents have a 25% chance of being affected, a 50% chance of being carriers (having one normal and one mutated copy), and a 25% chance of being unaffected.
**Why the Correct Answer is Right:**
In this question, we are discussing the probability of offspring being affected by an autosomal recessive disorder if the parents are carriers. Since the inheritance pattern requires two mutated alleles (genes) for an individual to be affected, the chances of an affected offspring are dependent on the parents' genotype (the combination of alleles they carry).
Given options for the parents' genotypes:
A. Both parents are carriers (heterozygous): AA (one normal allele and one mutated allele) or aa (two mutated alleles)
B. Parent 1 is affected and Parent 2 is a carrier (heterozygous): Aa
C. Parent 1 is affected and Parent 2 is homozygous normal (both normal alleles): aa
D. Parent 1 is a carrier and Parent 2 is affected (heterozygous): Aa
**Why Each Wrong Option is Incorrect:**
A. Parents are both carriers (heterozygous) - The chances of an affected offspring are 25%, as in this scenario, both parents carry only one mutated allele each. This means one affected offspring will still have a 50% chance of being a carrier, not affected, or unaffected.
B. Parent 1 is affected and Parent 2 is a carrier (heterozygous) - This scenario has a 25% chance of having an affected offspring, as in this case, one parent carries two mutated alleles (affected) and the other carries only one mutated allele (a carrier).
C. Parent 1 is affected and Parent 2 is homozygous normal (both normal alleles) - In this scenario, both parents carry two normal alleles, which means there is zero chance of an affected offspring.
D. Parent 1 is a carrier and Parent 2 is affected (heterozygous) - This scenario has a 25% chance of having an affected offspring, as in this case, one parent carries two mutated alleles (a carrier) and the other carries two mutated alleles (affected).
**Clinical Pearl:**
Inheritance of autosomal recessive disorders is a matter of chance, influenced by the parents' genotype. Parents who are carriers have a 25% chance of having an affected child. It is essential for potential parents to undergo pre-marital genetic counseling to understand their risk of having a child with a genetic disorder and to make an informed decision regarding their reproductive choices.