Theory question 104
Mendelian Inheritance(a) List four characteristics which can be genetically transmitted in humans.
(b)(i) Name two sites each in plants and animals where meiosis occurs.
(ii) State two differences between meiosis and mitosis.
(c) A woman with blood group 'A' (heterozygous) claimed that her son who has blood group 'O' was fathered by Mr. James who has blood group 'A' (homozygous). With the aid of suitable genetic diagrams
(i) prove or disprove the woman's claim; (ii) give reasons to support your answer.
Show the model answer
(a) Any four: blood group; skin colour/albinism; tongue rolling; eye colour; height; sickle-cell trait; haemophilia; colour blindness; ear lobe shape.
(b)(i) Plants: anther (pollen mother cells) and ovule/nucellus (embryo sac mother cell). Animals: testes and ovaries.
(ii) Meiosis gives four daughter cells, mitosis two; meiosis halves the chromosome number (haploid), mitosis keeps it (diploid); meiosis has two divisions, mitosis one; in meiosis crossing over occurs, giving genetically different cells, while mitosis gives identical cells; meiosis occurs in reproductive organs, mitosis in body cells.
(c)(i) Woman IAIO × Mr. James IAIA; gametes IA, IO and IA; offspring IAIA and IAIO — all blood group A. The claim is false.
(ii) A group O child must be IOIO, receiving one IO from each parent; Mr. James is homozygous IAIA and has no IO allele to pass on, so he cannot be the father.
Show parents, gametes and offspring in the genetic diagram.