10 5 Blood type is an example of inherited variation. Blood types A, B, AB and O are determined by a single gene. Blood types are due to the presence or absence of antigens on the cell surface membranes of red blood cells. These antigens are glycoproteins. (a) The diagram shows the structure of a cell surface membrane. R Q P S (i) Which of these labels identifies a glycoprotein? (1) A P B Q C R D S Turn over 11 (ii) The alleles that produce blood type antigens A and B are codominant. A person with the genotype IAIB has blood type AB. The allele producing blood type O is recessive. A couple have been told that the probability of having a child with blood type AB is 0.25 and the probability of blood type O is 0.25. Deduce the genotypes and phenotypes of the parents in the table, by using a genetic diagram. (3) Parent Genotype Phenotype 1 2 12 (b) The production of the blood type antigens involves molecules of mRNA and tRNA. (i) Which row in the table describes the structure of tRNA? (1) Bases Number of strands Type of sugar A A, C, G, U 1 deoxyribose B A, C, G, U 1 ribose C A, C, G, T 2 deoxyribose D A, C, G, T 2 ribose (ii) Mononucleotides all contain a base and a sugar as part of their structure. Name the other component of all mononucleotides. (1) ..................................................................................................................................................................................................................................................................................... (iii) The mononucleotides of mRNA are joined together by RNA polymerase. Which part of the eukaryotic cell is the location for this process? (1) A cytoplasm B mitochondrion C nucleus D rough endoplasmic reticulum Turn over 13 (iv) Describe the role of the tRNA in the production of the protein part of a glycoprotein. 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(c) Antigens on the cell membranes of microbes can stimulate endocytosis and exocytosis in white blood cells. These processes are involved in transport through a cell surface membrane. Give two differences between endocytosis and exocytosis. 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(Total for Question 5 = 11 marks) 14 BLANK PAGE