Outline how a protein is made in a cell by the process of translation.

A family has a history of hemophilia that is caused by a sex-linked recessive allele. A woman from this family is a carrier and marries a man who does not have the allele. Showing your working, determine the probability of their children having the disease.

Explain how blood clotting occurs and the consequence for a person who has hemophilia.

1. translation occurs on ribosomes when proteins/polypeptides are synthesized;
2. amino acid sequence of a protein is determined by the mRNA;
3. mRNA is determined by the order of bases of DNA/order of bases sequence in a gene;
4. codons (of 3 bases) on mRNA correspond to one amino acid in a polypeptide;
5. codons are on mRNA and anticodons on tRNA;
6. mRNA binds to ribosome/(during initiation) small ribosomal subunit binds to the start of the mRNA sequence;
7. tRNA transfers an amino acid to large ribosomal subunit/to the ribosome;
8. reference to start or stop codon;
9. tRNA moves to the next mRNA codon to continue the process, creating an amino acid chain;
10. peptide bond formed between amino acids
11. translation/order of amino acids depends on complementary base pairing between codons and anticodons;

1. alleles clearly labelled for both parents (in a Punnett square or other format);
2. correct genotypes for all four possibilities for children;
   
3. phenotypes of the children: the sons would have a 50 % chance of having hemophilia and the daughters would have 0 % chance of having hemophilia/50 % chance of being a carrier;

Sex needs to be mentioned for mpc but info can be taken from the Punnett square.

       Clotting process:

1. blood clotting seals cuts in the skin;
2. clotting factors are released (from platelets);
3. thrombin is activated;
4. a cascade reaction occurs (with thrombin);
5. (thrombin causes) fibrinogen is converted to fibrin;
6. fibrin forms a clot/blocks the cut/prevents blood from being lost;
   Consequences of hemophilia:
7. if a person does not have enough clotting factors/hemophilia, the clot will not form;
8. pathogens can enter the body more easily;
9. (in hemophiliacs) blood will be lost from a cut which affects blood pressure/bleeding to death;
10. loss of blood affects amount of hemoglobin/O₂ carried around the body;
11. reference to lifestyle / menstrual/birth problems

e.g. surgery, contact sports

Well prepared candidates were able to clearly explain the production of a protein by translation. Weak candidates usually scored a few points. Many started with a very detailed description of transcription, which was not necessary and put them in danger of losing the quality mark.

A standard sex -linked genetics question. It was expected that an indication that half of the boys would suffer from haemophilia, not just a ‘25 % possibility’.

The formation of a clot by the final formation of fibrin was reasonably well known, although many implied that the thrombin directly converted the fibrinogen and did not mention the cascade of reactions. In the consequences for haemophiliacs the fact that the clot would not form and they risked bleeding to death and were more susceptible to infections were well known. There were some G2 comments that 7 marks seemed difficult to attain, this did not seem to be the case with an average of 4.1 marks for the question.