Question

Explain why disorders caused by dominant alleles on autosomes are less common than those caused by recessive alleles on autosomes

Answer 1

Autosomal dominant disorders are less common than autosomal recessive disorders because dominant disorders are expressed with just one copy of the faulty allele, potentially reducing reproductive success, while recessive disorders require two copies, thus carriers can pass the allele unnoticed, keeping it in the population.

Step-by-step explanation:

Disorders caused by dominant alleles on autosomes, such as Huntington's disease and neurofibromatosis, are generally less common than those caused by recessive alleles. This is because individuals with a single dominant allele will express the disorder, making it more likely to affect the individual's health and potentially reduce their reproductive success. A person with a dominant disorder is also more likely to be diagnosed and possibly receive medical advice to avoid passing it to offspring. Conversely, autosomal recessive disorders like cystic fibrosis or Tay-Sachs disease require two copies of the recessive allele to be expressed. Therefore, carriers who are heterozygous for the recessive allele do not show symptoms and can unknowingly pass the allele to their offspring. The condition remains hidden in the gene pool and may be passed through several generations before two carriers mate and produce an offspring with the disorder, making it more prevalent in a population.

In autosomal recessive inheritance, a child must inherit two copies of the faulty allele to express the disorder. Since carriers can outnumber those affected, the recessive allele can persist in the population at higher rates without being expressed phenotypically in all carriers. Additionally, some recessive disorders confer a survival advantage in heterozygous individuals in certain environments, such as the sickle cell trait providing resistance to malaria. This helps maintain the presence of the allele in the gene pool.

Answer 2

Disorders caused by dominant alleles on autosomes are less common than those caused by recessive alleles on autosomes

Step-by-step explanation:

Based on the Mendelian inheritance pattern,

Autosomal dominant allele will affect a person if any one of the parent is affected.

Autosomal recessive allele will affect a person only both the parents are carriers.

Autosomal diseases caused by dominant allele can occur in every generation and from that of recessive allele may not occur in every generation according to Mendel’s laws of inheritance.

However, many inherited disorders are more common due to recessive alleles. When only one copy of the DNA carried by one parent is passed, it is mostly harmless and may sometime get eliminated through natural selection process of evolution. The chances of inheritance is only around 50% and children who do not inherit will neither develop any such disease or can pass the genes of the disease.

Although recessive, if both the parents are carrier, then the chances of inheritance doubles and hence recessive allele autosomal disorders occur more frequently. Inherited diseases like cystic fibrosis, sickle cell anemia caused by recessive allele is more common than diseases like Marfan’s syndrome caused by dominant allele.