Question

Two children, a brother and his sister, are born with an autosomal recessive condition. They are believed to be the first two individuals in their extended family to have this disorder. What is the most likely genotypes for their parents?

a)The father is likely heterozygous for the disorder, and the mother is likely homozygous for the disorder.
b)The mother is likely heterozygous for the disorder, and the father is likely homozygous for the disorder.
c)The mother is likely homozygous for the normal genotype, and the father is likely heterozygous for the disorder.
d)The father is likely homozygous for the normal genotype, and the mother is likely heterozygous for the disorder.
e)Both parents are likely heterozygous for the disorder.

Answer 1

The most likely genotypes for the parents of two children with an autosomal recessive condition are that the mother is heterozygous for the disorder and the father is homozygous for the normal genotype.

Step-by-step explanation:

When two children are born with an autosomal recessive condition, it suggests that both of their parents are carriers of the disorder. In this scenario, the most likely genotypes for the parents would be that the mother is heterozygous for the disorder (Aa) and the father is homozygous for the normal genotype (AA). This means that the mother has one normal allele and one disease allele, and the father has two normal alleles.

Answer 2

The most likely genotypes for the parents of two children with an autosomal recessive disorder are that both parents are heterozygous carriers of the disorder.

Step-by-step explanation:

When dealing with an autosomal recessive condition, and noting that both siblings are affected by this disorder, it suggests that the disorder manifests only when an individual has two copies of the recessive allele (homozygous recessive). If the condition is autosomal recessive, both parents must at least be carriers of one copy of the recessive allele. Carriers are heterozygous, meaning they have one normal allele and one allele for the disorder. They do not display symptoms because the normal allele is phenotypically dominant.

Since each parent must pass on the recessive allele for the condition to manifest in their children, the most likely genotypes of the parents are both heterozygous for the disorder (Aa). Therefore, each parent has a 50% chance of passing on the recessive allele, and the likelihood of both siblings inheriting the disorder is 25% (based on a Punnett square analysis). This aligns with the principle that for such a genetic disorder to appear in an individual, he or she must inherit the defective gene from both parents.

Answer to the Student's Question:

The most likely genotypes for the parents of two children born with an autosomal recessive condition are that both parents are likely heterozygous for the disorder (option e).