Theory question 104
Mendelian Inheritance(a) List four characters which can be transmitted from parent to offspring in man
(b) State two differences between mitosis and meiosis
(c) Explain briefly the importance of meiosis and fertilization in the reproduction of organisms
(d) In a monohybrid cross between a pure breeding plant that produces blue flowers and a pure breeding plant that produces white flower, the F1 generation produced only blue flowers. By means of labelled cross diagrams, state the type of flowers you would expect if the F1 generation is (i) self-pollinated (ii) cross-pollinated with a pure breeding plant that produces white flowers. Give reasons for your answers in (d) (i) and (ii)
Show the model answer
(a) Any four: skin colour, height, eye colour, blood group, tongue rolling, sickle cell trait, albinism, hair colour/texture, colour blindness
(b) Any two: mitosis gives two daughter cells, meiosis four; mitosis keeps the diploid number, meiosis halves it (haploid); mitosis in body cells, meiosis in reproductive organs; no crossing over in mitosis, crossing over in meiosis; daughter cells of mitosis identical, of meiosis different
(c) Meiosis halves the chromosome number in gametes so that fertilisation restores the diploid number, keeping it constant from generation to generation; both bring about new combinations of genes, causing variation
(d) Let B = blue (dominant), b = white; parents BB × bb, F₁ all Bb (blue)
(i) Bb × Bb → BB, Bb, Bb, bb: 3 blue : 1 white – each parent gives B or b and the dominant blue shows whenever B is present
(ii) Bb × bb → Bb, Bb, bb, bb: 1 blue : 1 white – the white parent gives only b, so half the offspring are bb (white)
Show parents, gametes and offspring in each cross diagram, with a key to the symbols.