Punnett Squares for X-Linked Disorders

Punnett Squares and Genetic Disorders

• In Square A, the mother is a carrier of the disorder.
• In Square B, the father is affected by the disorder.
• The probability of producing a genotypically and phenotypically normal daughter in Square A is 1/2 or 50%.
• Down syndrome is classified as an autosomal trisomy disorder.
• Down syndrome can be diagnosed prenatally through techniques such as chorionic villus sampling (CVS) and amniocentesis.
• The karyotype of an individual with Down syndrome is 47, XY or 47, XX.

Autosomal Dominant Disorders

• In the Punnett square where 'H' represents an autosomal dominant disorder, the probability that this couple will produce a child with the disorder is 1/2 or 50%.
• The probability that this couple will produce a child who is phenotypically normal is 1/2 or 50%.
• The probability that this couple will produce a child who is a carrier of the disease is 1/2 or 50%.

Autosomal Recessive Disorders

• In the Punnett square where 't' represents an autosomal recessive disorder, the probability that this couple will produce a child who is not a carrier of the disorder is 1/4 or 25%.
• The parent who is more likely to be a carrier of the disorder in an autosomal recessive disorder, represented by 'T', is the mother.
• Autosomal recessive disorders are inherited in a recessive pattern, meaning that an individual must inherit two copies of the mutated gene (one from each parent) to express the disorder.

X-Linked Disorders

• X-linked recessive disorders show a higher probability of affecting males compared to females.
• A characteristic of X-linked recessive disorders is that the mother is typically a carrier of the disorder, while the father is unaffected.
• X-linked dominant disorders are rare and typically affect females more than males.

Inheritance Patterns

• Autosomal dominant disorders are inherited in a dominant pattern, meaning that an individual only needs to inherit one copy of the mutated gene to express the disorder.
• A carrier of a genetic disorder has a genotype of 'Tt' or 'Rs', meaning they have one normal and one mutated allele.

Key Differences

• The main difference between autosomal dominant and autosomal recessive disorders is the number of copies of the mutated gene needed to express the disorder (one for autosomal dominant, two for autosomal recessive).