Question

Achondroplasia is a rare form of dwarfism. It is caused by an autosomal dominant mutation within a single gene. Among \(1,422,000\) live births, the number of babies born with actoondroplasia was 31. Among those 31 babies, 18 of them had one parent with achondroplasia. The remaining babies had two unaffected parents. What is the mutation frequency for this disorder among these \(1,422,000\) babies? What is the mutation rate for achondroplasia?

Short answer

The mutation frequency for the disorder among these \(1,422,000\) babies is \(2.18 \times 10^{-5}\) and the mutation rate for achondroplasia is also \(2.18 \times 10^{-5}\)

Step-by-step solution

Calculate mutation frequency

The mutation frequency indicates how often a particular mutation is seen in a given population. It is calculated as the total number of instances of a mutation divided by the population size. In this case, the mutation frequency of achondroplasia can be calculated as the total number of babies born with achondroplasia divided by the total number of live births. Here, the number of babies with achondroplasia is 31 out of 1,422,000 live births. So, the formula is: Frequency = Number of cases / Total number of individuals = 31/1,422,000 = 0.000021 or \(2.18 \times 10^{-5}\).

Calculate mutation rate

Mutation rate usually refers to the chance that a gene will be altered by a new mutation. It is typically given for a specific gene and is measured as mutations per base pair per generation. In this case, the mutation rate is asked for a specific disorder and not for a specific gene. Therefore interpreting the mutation rate as the frequency in this specific context would be reasonable. Hence, it would be the same as the calculated frequency, which is \(2.18 \times 10^{-5}\).

Key concepts

Achondroplasia

Achondroplasia is a genetic disorder that is one of the most common causes of dwarfism. Individuals with achondroplasia have short stature, with an adult height averaging around four feet. The condition involves the conversion of cartilage into bone, particularly in the long bones of the arms and legs, which is affected by a mutation.

This mutation occurs in the FGFR3 gene, which is responsible for helping to control bone growth and maintenance. In achondroplasia, the mutated gene causes an abnormality in the protein that results in halted or slowed growth of the long bones.

Effects on an individual's health can range from milder symptoms like bowed legs and shorter fingers to more significant health issues such as spinal stenosis and hydrocephalus. Despite these challenges, people with achondroplasia can lead full and active lives with proper medical attention and support.

Autosomal Dominant Mutation

An autosomal dominant mutation is a type of genetic alteration that occurs on one of the 22 autosomal (non-sex) chromosomes. 'Dominant' means that only one copy of the mutated gene, from just one parent, is necessary for an individual to express the trait associated with the mutation.

These mutations can be inherited from an affected parent or can occur as a spontaneous mutation, where neither parent has the mutation present in their germ cells. Examples of autosomal dominant diseases include achondroplasia, Huntington's disease, and Marfan syndrome.

In instances of achondroplasia, the mutation in the FGFR3 gene dominates over the non-mutated version of the gene. This means that a child only needs to inherit one mutated gene to display the characteristics of achondroplasia. If one parent has achondroplasia and the other does not, there is a 50% chance their child will inherit the condition.

Mutation Rate

Mutation rate is a measure of the frequency at which a new mutation occurs in a DNA sequence per generation. It's usually expressed as mutations per nucleotide per cell division. For disorders like achondroplasia, it can be more practical to consider the rate at which new cases occur in a population due to new mutations.

Calculating mutation rates is essential for understanding the dynamics of genetic diseases, whether they are increasing or decreasing over time, and for gauging the effects of ecological and biological factors on genetic health. Factors that can influence mutation rates include environmental exposures, such as radiation or chemicals, and biological factors, such as errors during DNA replication.

Genetics Population Study

Genetics population studies are research methods that look at the frequencies of genes and alleles within a population to gauge the prevalence and distribution of genetic traits and disorders. This type of study looks at aspects like mutation frequency and rate to understand the genetics of a population as a whole rather than focusing on individual cases.

The importance of population genetics studies in achondroplasia cannot be overstated. By analyzing mutation frequencies, researchers can determine not only how common the condition is but can also trace the occurrence of new mutations, and model predictions about future trends. These studies can inform public health decisions, guide screening recommendations, and underpin counseling individuals about their risks of having children with genetic disorders.