Genetics

1. INTERACTIVE MULTIPLE CHOICE QUESTIONS Genetics The answers are provided. Explanations of why the alternatives are unsatisfactory are also offered

2. These multiple choice questions are similar to the ones set by the GCSE and IGCSE Examination Boards except that, in some cases, there may be more than one acceptable answer For this reason, even if you select a correct answer at your first attempt, it is worth looking at all the alternatives (a) to see if there is a better answer and (b) to see why some of the alternatives are unacceptable

3. Question 1 (a) A (b) B (c) AB (d) O Question 2 A father’s blood group is AB; the mother’s is O. Which of the following blood groups could appear in their offspring?

4. Yes The father’s genome must be iAiB The mother’s genome will be iOiO The combination iAiO is possible and will be expressed as group A because iA is the dominant allele

5. Yes The father’s genome must be iAiB The mother’s genome will be iOiO The combination iBiO is possible and will be expressed as group B because iBis the dominant allele

6. No The father’s genome must be iAiB The mother’s genome will be iOiO The offspring will all inherit either iA or iB from their father and iO from their mother. Their genomes will be either iAiO (expressed as group A) or iBiO (expressedas Group B. Group AB is not possible

7. No The father’s genome must be iAiB The mother’s genome will be iOiO The offspring will all inherit either iA or iB from their father and iO from their mother. Their genomes will be either iAiO or iBiO.The alleles iA and iB are both dominant to iO so group O is not possible

8. Question 2 (a) 6 brown females and 6 black males (b) 9 black and 3 brown, all male (c) 6 black males and 6 black females (d) 12 black males Question 3 A pure-breeding male black mouse is mated with a female brown mouse and they produce a litter of 12. The allele for black fur is dominant to the allele to brown fur. What is the expected distribution of colour and sex in their litter?

9. No The pure-breeding male’s genome must be BB and the brown mouse’s genome must be bb. The allele for black fur is dominant over the brown allele. Therefore all the offspring will be black (Bb) gametes Black male Brown female B B b Bb Bb b bB bB

10. gametes Black male Brown female B B b Bb Bb b bB bB No As explained in the previous slide, the allele for black fur is dominant to the brown allele, so there can be no brown mice in the litter from this cross

11. Yes Inheritance of colour is explained in the first answer. The male mouse carries the X and Y chromosomes. The female mouse carries two X chromosomes. At meiosis, only one of each chromosome pair goes to the gametes. gametes Black male Brown female BX BY bX BbXX BbXY bX bBXX bBXY

12. No Certainly all 12 mice will be black as explained in the first answer, but the sex is inherited as explained in the third answer, so the expectation is that there will be 6 males and 6 females in the litter

13. Question 3 (a) All black (b) 6 black and 6 brown X (c) 4 black and eight brown (d) 8 black and 4 brown Question 4 A male heterozygous black mouse (Bb) is mated with a female heterozygous black mouse (Bb) and the litter consists of 12 pups. B is the allele for the black colour. The allele for brown colour is b. The dominant allele is B. Which of these ratios is closest to the expected ratio for the distribution of colour among the offspring?

14. Not very close From the Punned square you can see that the expected ratio is 3 black (BB or Bb) to 1 brown (bb) gametes B b BB Bb B b Bb bb These are only the chance combinations. It would be possible to produce 12 black pups, since ‘black’ is the dominant allele but this is not close to the expected ratio

15. Not very close From the Punnett square you can see that the expected ratio is 3 black (BB or Bb) to 1 brown (bb) gametes B b BB Bb B b Bb bb These are only the chance combinations. It would be possible to produce 6 black and 6 brown pups but this is not very close to the expected ratio of 9:3

16. Close but … From the Punnett square you can see that the expected ratio is 3 black (BB or Bb) to 1 brown (bb) gametes B b BB Bb B b Bb bb These are only the chance combinations. A combination of 4 black to 8 brown is close to the expected ratio of 3:9 but since black is the dominant allele it seems to be the wrong way round

17. The closest From the Punnett square you can see that the expected ratio is 3 black (BB or Bb) to 1 brown (bb) gametes B b BB Bb B b Bb bb These are only the chance combinations. A combination of 8 black to 4 brown is closest to the expected ratio of 9:3

18. Question 4 a (a) a b c d e (b) b a c e d d (c) b a d c e b (d) d b a c e Question 5 e c The diagrams represent stages in cell division by mitosis. (only one chromosome is represented). What is the correct sequence of events?

19. No The chromosomes shorten and thicken (b) after they have appeared in the nucleus (b). Similarly at the end of cell division, the chromosomes extend and become less visible (d) after the cell divides (e)

20. Yes This is the correct sequence

21. No The cell does not start to divide (d) until the chromatids have separated (c). Also, cell constriction (e) precedes cell division (d)

22. No Cell division (d) does not take place until the chromatids have appeared (b) and separated (c). Also, cell constriction (e) precedes cell division (d)

23. Question 5 (a) in skin cells (b) in red bone marrow (c) in reproductive organs (d) in lymphocytes Question 6 The process of cell division by meiosis takes place only…

24. No Although the cells in the basal layer of skin divide rapidly, it is by mitosis

25. No Cells in the red bone marrow divide rapidly to produce red and white blood cells, but this is by mitosis

26. Yes The cells in the reproductive organs which produce gametes will undergo a meiotic division and produce haploid gametes

27. No The lymphocytes are capable of dividing rapidly to produce clones of cells but this involves only mitosis

28. Question 6 (a) thymine (b) guanine (c) valine (d) cytosine Question 7 In a DNA molecule, which of the molecules listed below pairs with adenine?

29. adenine thymine Yes

30. cytosine guanine No Guanine pairs with cytosine

31. No Valine is an amino acid and not an organic base

32. guanine cytosine No Cytosine pairs with guanine

33. Question 7 (a) Long, white, straight fur (b) Short, black, straight fur (c) Long, white, curly fur (d) Long, black, curly fur Question 8 If L is the allele for long hair and l is the allele for short hair, B is the allele for black hair and b is the allele for white hair, S is the allele for straight hair and s is the allele for curly hair What will be the phenotype for a small dog with the genotype LLBbss?

34. No The allele for black fur is dominant to the allele for white fur

35. No The dog carries both dominant alleles for long hair

36. No The dog is heterozygous for the colour gene, but the allele for black fur is dominant to the allele for white fur

37. Yes The dog is homozygous recessive for the curly allele, homozygous dominant for hair length and heterozygous for the colour gene but the black allele is dominant

38. Question 8 (1) e, b, d, a, c (3) b, e, a, d, c (2) b, c, e, a, d (4) b, d, e, a, c Question 9 Bacteria can be genetically modified to produce human insulin. The steps involve … (a) cutting out the insulin gene from human DNA with restriction enzymes, (b) extracting plasmids from the bacterium, (c) returning the modified plasmid to the bacterium, (d) inserting the insulin gene into the plasmid, (e) cutting open the plasmid with the same restriction enzyme Which of the following is the correct sequence?

39. No The plasmids cannot be cut open (e) until they are extracted from the bacterium (b)

40. No The insulin gene must be inserted in the plasmid (d) before it is returned to the bacterium (c)

41. Yes This is the correct sequence b, a, e, d, c would also be acceptable because the restriction enzyme can cut the plasmid DNA and human DNA in any order

42. No The plasmid DNA must be opened (e) before the insulin gene can be inserted (d)

43. Question 9 (a) a gene mutation or (b) a change of habitat or (c) a gene recombination or (d) a climate change Question 10 Before natural selection can take place in an animal, there has to be either …

44. Yes A gene mutation which caused a change in the organism could be subject to natural selection

45. No A change of habitat might favour a variation resulting from a genetic change, such as a mutation, but selection could not result from an organism simply changing its habitat

46. Yes A new combination of genes could produce a variation that had a selective advantage

47. No A climate change might favour some variants in a population but could not, itself, produce those variants. There has to be a genetic change for the climate change to act upon

48. Question 10 (a) Cystic fibrosis (b) AIDS (c) Sickle cell disease (d) Tuberculosis Which of the following can be inherited?

49. Yes Cystic fibrosis is caused by a gene mutation. The gene controls the movement of salts and water into and out of the cells. The mutated form of the gene causes thick mucus to be secreted by the lungs, airways and pancreas, plus many other symptoms. The mutated gene is recessive to the normal gene..

50. No AIDS is caused by a virus, the human immunodeficiency virus (HIV). The virus is transmitted by sexual intercourse or by infected syringe needles. An infected mother may pass the disease on to her baby, so the disease may, superficially, appear to be inherited