Photo AI
Individuals with sickle cell disease have a form of haemoglobin called haemoglobin S, which is less efficient at carrying oxygen - Scottish Highers Human Biology - Question 4 - 2023
Question 4
Individuals with sickle cell disease have a form of haemoglobin called haemoglobin S, which is less efficient at carrying oxygen. The diagram shows how a mutation i... show full transcript
Worked Solution & Example Answer:Individuals with sickle cell disease have a form of haemoglobin called haemoglobin S, which is less efficient at carrying oxygen - Scottish Highers Human Biology - Question 4 - 2023
Step 1
Describe evidence from the diagram that supports this statement.
Answer
In the diagram, the substitution mutation is indicated by the fact that one base in the DNA sequence has been replaced. Specifically, the DNA sequence for normal haemoglobin shows 'G C C' while the haemoglobin S sequence shows 'G T C', meaning that one thymine (T) base is substituted for adenine (A) in the mRNA coding.
Step 2
Suggest how changing one amino acid could cause the haemoglobin S protein to function less effectively than haemoglobin.
Answer
Changing one amino acid can alter the protein's overall shape and structure. For instance, if valine is substituted for glutamic acid in the haemoglobin S protein, the new shape may not facilitate the effective binding of oxygen, thereby reducing the protein's functionality compared to normal haemoglobin.
Step 3
Compare the effects of frame-shift and missense mutations on the resulting sequence of amino acids in a protein.
Answer
A missense mutation affects only one amino acid in the protein sequence, replacing it with another, which may alter the protein's function. In contrast, a frame-shift mutation changes the entire reading frame, potentially altering the sequence of all subsequent amino acids, leading to a completely different and usually nonfunctional protein.
Step 4
Explain why the inheritance of sickle cell trait is an example of incomplete dominance.
Answer
The inheritance of sickle cell trait demonstrates incomplete dominance because both alleles (haemoglobin S and normal haemoglobin) are expressed in the phenotype. Individuals with the HS genotype show an intermediate phenotype, where both types of haemoglobin are present.
Step 5
Suggest why individuals with sickle cell disease have an increased risk of having a stroke.
Answer
Individuals with sickle cell disease have an increased risk of stroke because their sickle-shaped red blood cells can obstruct blood flow in the small blood vessels, which may lead to blood clots and impaired circulation to the brain.
Step 6