76. Inherited Disorders and Embryo Screening

Inherited disorders are conditions passed from parents to offspring through specific alleles. Two primary examples are Polydactyly and Cystic Fibrosis.

1. Polydactyly

Polydactyly is a condition where a person is born with extra fingers or toes.

• Inheritance: Caused by a dominant allele.

• Expression: You only need one copy of the allele to have the disorder.

• Example Cross: If a heterozygous parent (Aa) mates with a normal parent (aa), there is a 50% chance (1:1 ratio) that the offspring will have polydactyly.

2. Cystic Fibrosis

Cystic Fibrosis is a disorder of the cell membranes that causes the body to produce thick, sticky mucus, primarily affecting the lungs and pancreas.

• Inheritance: Caused by a recessive allele.

• Expression: You must have two copies of the recessive allele to have the disease.

• Carriers: People who are heterozygous (Ff) do not have the symptoms but "carry" the gene and can pass it to their children. About 1 in 25 people are carriers.

• Example Cross: If two carriers (Ff x Ff) mate, the results are:

  • 25% (1 in 4) Unaffected (FF)

  • 50% (2 in 4) Carriers (Ff)

  • 25% (1 in 4) Have Cystic Fibrosis (ff)

3. Embryo Screening

During IVF (In Vitro Fertilization), cells can be taken from an embryo to analyze its genes before it is implanted in the uterus. This is called embryo screening.

Advantages:

• Reduces Suffering: Fewer people are born with life-altering or painful health problems.

• Economic Benefit: Treating genetic disorders is very expensive for healthcare systems; screening can save significant costs.

Disadvantages and Concerns:

• Prejudice: It may imply that people with genetic disorders are "undesirable," potentially increasing social stigma.

• Ethical Slope: There is a concern that people might eventually screen for non-medical traits like eye color or height (often called "designer babies").

• Note: In many regions, including the UK, there are strict laws to prevent screening for anything other than serious medical conditions.

Summary Table: Comparing Inherited Disorders