Solved: A family has a history of hemophilia that is caused by a sex-linked recessive... [IB Biology]

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.

[3]

Verified

Solution

Alleles clearly labelled for both parents (in a Punnett square or other format);
Correct genotypes for all four possibilities for children;

	father
mother	$X^H$	$Y$
$X^h$	$X^H X^h$	$X^h Y$
$X^H$	$X^H X^H$	$X^H Y$

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.

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

[5]

Verified

Solution

Translation occurs on ribosomes when proteins/polypeptides are synthesized 1 mark
Amino acid sequence of a protein is determined by the mRNA 1 mark
mRNA is determined by the order of bases of DNA/order of bases sequence in a gene 1 mark
Codons (of 3 bases) on mRNA correspond to one amino acid in a polypeptide 1 mark
Codons are on mRNA and anticodons on tRNA 1 mark
mRNA binds to ribosome/(during initiation) small ribosomal subunit binds to the start of the mRNA sequence 1 mark
tRNA transfers an amino acid to large ribosomal subunit/to the ribosome 1 mark
Reference to start or stop codon v
tRNA moves to the next mRNA codon to continue the process, creating an amino acid chain 1 mark
Peptide bond formed between amino acids 1 mark
Translation/order of amino acids depends on complementary base pairing between codons and anticodons 1 mark

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

[7]

Verified

Solution

Blood clotting seals cuts in the skin 1 mark
Clotting factors are released (from platelets) 1 mark
Thrombin is activated 1 mark A cascade reaction occurs (with thrombin) 1 mark
Fibrinogen is converted to fibrin 1 mark
Fibrin forms a clot/blocks the cut/prevents blood from being lost 1 mark
If a person does not have enough clotting factors/hemophilia, the clot will not form 1 mark
Pathogens can enter the body more easily 1 mark
(In hemophiliacs) blood will be lost from a cut which affects blood pressure/bleeding to death 1 mark
Loss of blood affects amount of hemoglobin/O $_2$ carried around the body 1 mark
Reference to lifestyle/menstrual/birth problems 1 mark

e.g. surgery, contact sports

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