A phenotype is the result of a particular genotype. Discuss how the genotype affects the phenotype by referring to proteins. The disease of...

There are several questions within your question. In order to make sure that all aspects of the question were answered, I broke the question into several segments and answered each part

     A. Genotype vs. phenotype

Genotypes are the allele combinations that an individual has for a particular trait or characteristic. A phenotype is the physical characteristic that results from the genotype that the individual has. Achondroplasia is an autosomal dominant pattern that is caused by a mutation of the FGFR3 gene. It is a form of short-limbed dwarfism.

In order to understand the above explanation an individual needs a clear understanding of some key terms within the answer. These are provided below.

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  Genes are segments of DNA. DNA stands for deoxyribose nucleic acid. DNA is made of smaller building blocks called nucleotides. Each nucleotide consists of a deoxyribose sugar, a phosphate group, and a nitrogen base. There are four kinds of nitrogen bases in DNA. DNA’s nitrogen bases are adenine, thymine, cytosine, and guanine. The order of the nucleotides determines the gene that an individual will have.


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  Alleles are variations of genes. In basic genetics, individuals receive on allele from each parent for each trait. Thus, most human characteristics are a result of two alleles.  Alleles can be dominant or recessive. Dominant genes are the “stronger” variety of the gene, while recessive alleles are considered to be “weaker”. Dominant alleles are represented with a capital letter. Recessive alleles are represented with lowercase letters.


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  Genotypes refer to the allele combinations that an individual contains.


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  Phenotypes are the physical characteristics represented by genotypes.


• Genotypes can be homozygous dominant, heterozygous, or homozygous recessive. If homozygous dominant, an individual has a genotype with two dominant alleles and will show the dominant phenotype. If heterozygous, an individual has one dominant and one recessive allele. Because a dominant allele is present, the individual will show the dominant phenotype. Homozygous recessive genotypes contain two recessive alleles. This is the only way that an individual can manifest the recessive phenotype when dealing with basic genetics.

Thus, an individual can have a genotype that is either homozygous dominant or heterozygous in order to display the achondroplasia phenotype.

        B. How does genotype affect phenotype in regards to proteins?

The genetic code (genotype) that lies within the DNA of an organism determines that proteins that are produced. The central dogma of biology states that DNA contains the key for RNA, which then codes for proteins.

Transcription and translation are the two phases of protein synthesis.

During transcription, the two strands of DNA unwind. One of the strands serves as a template for make an mRNA strand. Each set of three nucleotides on an mRNA is called a codon. These codons will be important in the second phase of protein synthesis called translation.

After the mRNA that is created during transcription, it migrates to the cytoplasm via a nuclear pore. 

During translation, mRNA, ribosomes, rRNA, tRAN, and amino acids work together to make the protein strand.

Once in the cytoplasm, the mRNA and ribosomes attach. The ribosomes serve as scaffolds that match the codons on mRNA’s to the anticodons on the tRNA’s. Anticodons are sets of three nucleotides on the base of a tRNA that are complementary to mRNA codons. On the top if tRNA are amino acids.

As the ribosome moves down the mRAN during translation, additional tRNA anticodons are matched with the complementary mRNA codons. In this way, amino acids that form a protein are arranged in the correct order.  When two amino acids are adjacent to one another, a peptide bond forms. The polypeptide chain continues to grow until a stop codon is reached.

       C. In terms of achondroplasia, provide a comparison of affected vs. unaffected persons.

As stated above, achondroplasia is an autosomal dominant pattern that is caused by a mutation of the FGFR3 gene. It is a form of short-limbed dwarfism. Being dominant, only one allele is required in order for the phenotype to be expressed. Thus, an individual can have a genotype that is either homozygous dominant or heterozygous in order to display the achondroplasia phenotype.

Individuals with achondroplasia have difficulty converting cartilage to bone. Thus, in comparison to individuals without the condition, people with achondroplasia display a short stature. Achondroplasia is also associated with a limited range of motion at the elbows, an enlarged head, and a prominent forehead.  People with achondroplasia may also suffer from apnea, obesity, and spinal stenosis.