Name: Chromosomes and Inheritance. Date: Time: 2 hours 30 minutes. Total marks available: 150. Total marks achieved:

Transcription

1 Name: Chromosomes and Inheritance Date: Time: 2 hours 30 minutes Total marks available: 150 Total marks achieved:

2 Q1. Human blood group is an example of a phenotype determined by alleles that show codominance. The table shows the different blood groups and their genotypes. (a) Explain what is meant by the term codominance (b) A man with blood group A married a woman with blood group B. They had four children, each with a different blood group. Use a genetic diagram to show this cross. (3) Genotypes of the parents Gametes Genotypes of the offspring

3 (Total for question = 4 marks) Q2. Most simple genetic crosses, such as those studied by Mendel, investigate phenotypes determined by a pair of alleles, where one allele is dominant over the other allele. Mendel crossed homozygous tall pea plants with homozygous dwarf pea plants. All the offspring were tall. (a) Use a genetic diagram to show the parent genotypes, the gametes formed and the genotypes of the offspring. (3) (b) Mendel then made sure that the tall offspring plants could only self-pollinate, rather than being pollinated by other plants. The seeds produced grew to give new plants with a 3 : 1 phenotypic ratio. (i) Suggest how Mendel made sure that the pea plants self-pollinated (ii) Give the genotypes of the offspring he obtained from the self-pollinated pea plants (c) What is meant by the term dominant allele?

4 (d) Some phenotypes are controlled by codominant alleles. What is meant by the term codominant alleles? (Total for question = 9 marks) Q3. Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

5 (a) Name one base found in DNA (line 3).... (b) Suggest why explants are sterilised (line 4)....

6 (c) Suggest why amino acids are provided in the growth medium (line 5).... (d) What is meant by the term pathogen (line 10)?... (e) Suggest two reasons why growers prefer to use micropropagation rather than sexual methods of reproduction to produce good quality flowers (lines 11 to 14) (f ) Suggest what is meant by the term sustainable energy source (lines 19 and 20) (g) The destruction of habitat can lead to extinction of species.

7 Give three other disadvantages of deforestation. (3) (Total for question = 11 marks) Q4. Emperor penguins live in the southern Polar Regions. The temperature here can be as low as 30 C. They have a number of adaptations that enable them to survive in such a cold climate.

8 (a) Fully grown penguins are large, often weighing up to 30 kg. Most other birds are much smaller. Explain how being large helps the penguin to survive at very low temperatures (b) Penguins also have soft downy feathers and a thick layer of fat just below the skin. Suggest how these features help penguins to survive

9 (c) One part of the penguin that is especially exposed to the cold is their feet. The muscles that operate the feet are located in the penguin's body rather than in the feet themselves. (i) Suggest how this benefits the penguin. (3) (ii) The penguin's feet move when the muscles pull on string-like structures called tendons. Suggest a property that these tendons should have

10 (d) Penguins huddle together to maintain their body temperature. Explain how this behaviour is an advantage to penguins (Total for question = 10 marks) Q5. The following passage describes inheritance. Complete the passage by writing a suitable word or words on each dotted line. (6) A gene is a section of a double-stranded molecule known as.... This molecule is found within the... of the cell, contained in threadlike structures called.... The two strands form a double helix linked by a series of paired bases. The base adenine is always linked to... and the base cytosine is always linked to.... Sometimes the genetic material of a cell changes. This is known as a....

11 These changes occur very rarely but their incidence can be increased by chemicals or ionising radiation. (Total for question = 6 marks) Q6. Frances likes to spend time in her garden. She grows many different types of flowering plants. (a) Explain how each of the following factors could affect the growth of a flowering plant. (i) Height of the parent plants (ii) Microorganisms in the soil (b) Frances says that she likes to keep her grass lawn free of weeds. (i) Suggest what Frances means by the word weed.

12 (ii) Explain why removing the weeds from her lawn would improve the quality of the grass plants (iii) How could Frances reduce the number of weeds in her lawn? (Total for question = 8 marks) Q7. The diagram shows the female reproductive system.

13 (a) Put a cross in the correct box to show (i) where the egg is released A B C D (ii) where the egg is fertilised A B C D (iii) where the embryo becomes surrounded by amniotic fluid A B C D

14 (b) The diagram shows a fertilised egg dividing into an embryo. (i) What is another name used to describe a fertilised egg?... (ii) Name the type of cell division used to produce the embryo.... (iii) Complete the table by ticking the box that shows the correct description of each cell in the embryo. (c) Describe how the developing embryo is supplied with nutrients. (3)......

15 (Total for question = 9 marks) Q8. Achondroplasia is an inherited condition in humans. Adults with achondroplasia are much shorter than average height. This condition is controlled by a gene with two alleles. The dominant allele (A) codes for shorter than average height and the recessive allele (a) codes for average height. (a) Two parents both had achondroplasia. They had a child who grew up to be of average height. Use a genetic diagram to show: the the the the genotype of each parent gametes they produced genotypes of all the possible offspring phenotypes of all the possible offspring (4) (b) The parents had a second child. State the probability that this child grew up to be of average height.... (c) Achondroplasia is caused by a dominant allele. (i) Explain what is meant by the term dominant allele.

16 (ii) Suggest why the number of people with achondroplasia is low, even though it is a dominant condition (Total for question = 9 marks) Q9. (a) There are several different stages during the process of human reproduction. Some of

17 these stages are shown in the box. Complete the table by writing the name of the stages in each empty box to show the correct order in which they occur. (4) (b) The diagram shows a section through the heart of a fetus. The arrows show the direction of blood flow. Describe two differences, shown in the diagram, between the heart of a fetus and an adult heart.

18 (c) The sex chromosomes in the cells of a mother are XX. The sex chromosomes in the cells of a father are XY. (i) Use this information to give the sex chromosomes in the cells of their male fetus.... (ii) Give the number of chromosomes in a body cell of the male fetus.... (Total for question = 8 marks) Q10. Mendel crossed together pure breeding pea plants with purple flowers and pure breeding pea plants with white flowers. The offspring plants all had purple flowers. (a) Explain which phenotype is dominant

19 (b) In a second cross, the purple offspring plants were self-pollinated (pollen from a flower put on the stigma of the same flower). Suggest how Mendel made sure that all the purple offspring plants were self-pollinated (c) (i) Use a genetic diagram to show the ratio of plants expected by crossing the purple offspring plants in part (b). Show the parental genotypes and gametes, and the offspring genotypes and phenotypes. Use F and f to represent the alleles. (4) Parent genotypes Gametes Offspring genotypes

20 Offspring phenotypes (ii) The plants actually produced in this cross were 36 purple and 8 white flowered plants. Calculate the ratio of purple to white flowered plants. Answer... (iii) Suggest why the actual ratio of phenotypes differs from the one predicted by your genetic diagram (d) A student suggested that purple flowers are more likely to be visited by bees than white flowers. Use your knowledge of natural selection to suggest how this might affect the number of purple and white flowers in the wild. (5)...

21 (Total for question = 16 marks) Q11. The photographs show an adult insect called an ash borer and an adult insect called a wasp.

22 Ash borers reproduce by laying eggs which develop into maggots. The maggots eat their way into ash trees and feed on carbohydrates in the trees. This can kill the trees because the root cells lack the carbohydrate needed to release energy for the absorption of mineral ions. (a) (i) Suggest why the maggots need to feed on carbohydrate (ii) Name and describe the process used by root cells to absorb mineral ions (iii) Describe how magnesium ions are used to help trees to grow.

23 (b) Wasps defend themselves from predators by using a sting. This means that predators avoid attacking wasps. Ash borers look very similar to wasps. Use your knowledge of natural selection to explain why ash borers have evolved to look like wasps. (4)

24 (Total for question = 9 marks) Q12. In mammals, males have two different sex chromosomes (X and Y) and females have two similar sex chromosomes (X and X). However, in birds males have two similar sex chromosomes (Z and Z), while females have two different sex chromosomes (Z and W). (a) Complete the genetic diagram to show how sex is inherited in birds. (4) (b) In birds, the egg is extremely large and contains food molecules that the growing embryo needs in order to develop.

25 (i) Suggest one food molecule that is present in a bird's egg and describe the role of this molecule in the growth of the bird embryo (ii) Suggest an advantage of the shell of the egg being made of a hard substance (iii) Chicken eggs are a rich source of vitamin A. Give another source of vitamin A and describe the function of vitamin A in humans

26 (c) The number of chromosomes in eggs and in sperm is less than the number of chromosomes in the body cells of animals. Explain how the number of chromosomes in animals is maintained in their offspring. (3) (Total for question = 12 marks) Q13. The diagram shows a human sperm cell.

27 (a) How many chromosomes are there in the nucleus?... (b) Respiration takes place in the middle piece of the sperm cell. Explain why respiration is important to a sperm cell (c) A sample of semen contains 40 million sperm cells. Only sixty percent of these sperm cells are capable of swimming. Calculate how many sperm cells in this semen sample are capable of swimming. Show your working.

28 Answer... (d) Some men are infertile because they do not produce enough sperm cells or the sperm cells they produce are not good swimmers. There is a test that can be used to find out if a man is infertile. Semen is added to a solution in a test tube. The test tube is then sealed. The solution stays purple if oxygen is present and changes to pink if oxygen is absent. The diagram shows how the test works. (i) A man used this test and the solution remained purple. What does this suggest about the man's sperm? Explain your answer

29 ... (ii) Suggest two reasons why the results of the test might not be correct (Total for question = 9 marks) Q14. (a) Lactose is a sugar found in milk. It is digested by an enzyme called lactase. Some people cannot make lactase. The condition they have is called lactose intolerance. The condition is caused by a recessive allele. This means that only people with the homozygous recessive genotype can be lactose intolerant. (i) What is meant by the term homozygous?... (ii) State the two possible genotypes of an individual who is not lactose intolerant. Use the symbols D for the dominant allele and d for the recessive allele

30 (b) (i) A homozygous dominant mother and a homozygous recessive father have two children. In the boxes below give the genotypes of the parents and their children. (ii) What is the probability that the children are lactose intolerant?... (c) People from different countries were tested to find out if they were lactose intolerant. The table shows the number of people who were tested in each country and the percentage who were lactose intolerant.

31 (i) The population size of country B is 190 million. Calculate the number of people in this country likely to be lactose intolerant. Show your working. Answer... (ii) Suggest a reason why the value of 100% for country H may not be correct.... (Total for question = 9 marks) Q15. Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

32 (a) Explain what is meant by the term gene (line 3).

33 (b) Suggest what is meant by the term superovulate (line 2) (c) In which part of the surrogate mother are the embryos implanted (lines 6 to 7)?... (d) Name the human behaviour that can lead to emphysema (line 11).... (e) What percentage of eggs produced by Tracy were known to contain transgenic DNA (lines 13 to 14)? (f ) (i) To be able to work, the blood clotting factors must be extracted from the milk.

34 Suggest why drinking milk containing blood clotting factors will not help to clot blood (line 17) (ii) Suggest why it is an advantage to increase the ability of cattle to digest cellulose (line 22) (g) Suggest the benefits of producing transgenic hearts. (3)

35 ... (Total for question = 12 marks) Q16. In fruit flies, the length of the wings is controlled by a gene with two alleles. The allele for long wings (L) is dominant to the allele for short wings (l). The diagram shows a long-winged fruit fly and a short-winged fruit fly. (a) Complete the table by writing the genotype, the description of genotype and the phenotype of the fruit flies. (3) (b) Two heterozygous fruit flies mated. The number of long-winged and short-winged offspring produced are shown below.

36 Tick one box to show the number of these offspring that is likely to be heterozygous. (c) Yeast cells feed on rotting fruit. Fruit flies feed on these yeast cells. Use this information to draw a food chain in the space below. (d) A student wanted to find out if fruit flies are attracted to rotting fruit. He set up this apparatus.

37 He released 20 fruit flies into the glass tank. After ten minutes, he counted the number of fruit flies found near the fresh fruit and the number found near the rotting fruit. The table shows his results. (i) Name two factors that the student should control in this investigation (ii) Do you think the student's results are reliable? Give a reason for your answer

38 ... (Total for question = 9 marks) Q1. Finally this question described the inheritance of A B O blood groups in humans. In part (a) about half of the responses correctly explained the meaning of codominance. Students did better in part (b) with most being able to identify the genotypes of the parents and gametes that would lead to 4 different blood groups in one family. Q2. Part (a) of this question tested candidates' understanding of a simple genetic cross. Most chose a sensible upper and lower case letter to represent the parental genotype but a surprising number chose different letters. In these cases, no mark was given to the parental genotype but the concept of transferred error was used to credit the gamete and offspring genotypes. In (b)(i), a pleasing number appreciated the need to keep the plants isolated, particularly from agents of cross-pollination such as insects. Many suggested that Mendel himself transferred pollen from the anther to the stigma of the same flower using a brush and due credit was given. Credit was also given to those candidates who described self-pollination. In (b)(ii), no credit was given for combinations of different letters such as T and D or T and d or T and S. Defining genetic terms is a challenge for students but many appreciated that a dominant allele is the one expressed in the heterozygote and that codominant alleles are both expressed in the heterozygote. Q3. This question this year explored the use of micropropagation in modern day biology. All the questions were attempted by students showing that they were able to access the content of the comprehension. Most were able to name one of the bases found in DNA though the spellings were often rather disappointing. In part (b) many appreciated that sterilising kills bacteria that otherwise might cause disease or have a detrimental effect on the growth of the explants. Most students appreciated that amino acids are fundamental in the manufacture of proteins. There were a lot of answers that gained no credit because they simply rephrased the stem of the question stating that amino acids

39 are needed for growth. Many students know that pathogens are disease causing microorganisms, but many lost credit by being too vague. For example, stating that pathogens are organisms that cause harm or illness is not sufficient. It was pleasing to note that most were able to suggest a meaningful definition of a sustainable energy source, with most using the phrase 'never runs out'. Some students wrote about the ecological benefits of sustainable energy sources but this was not credited. Answers to part (g) were pleasing with most answers making reference to leaching, soil erosion and global warming. Many had failed to read the question carefully and wrote about the consequences of habitat destruction and extinction. Q4. Here, candidates were given information about Emperor penguins. In (a), some candidates were able to explain that being large reduces the surface area to volume ratio and therefore reduces heat loss. In (b), many responses described the role of fat and down feathers as an insulator by trapping air. In (c)(i), candidates were asked to suggest why the muscles for the feet are located in the body of the penguin. Only the very best candidates were able to describe how the muscles would be warm and therefore enzymes could work at an optimum temperature to enable respiration and contraction. In (c)(ii), many thought that the tendons should be elastic rather than inelastic. In (d), most could explain why penguins huddle together with the best answers describing less exposure to cold, sharing body heat and decreasing the overall surface area to volume ratio. Q5. Candidates had to fill in the gaps with the appropriate word in a passage describing inheritance. Many scored full marks but some confused which bases paired with adenine and cytosine. Some spelling errors were tolerated with thymine and guanine, yet others could not be credited as they were not recognisable. Q6. This question described a situation in which the growth of flowering plants could be affected. In (a)(i), many gained marks for the idea of genes being passed on or were able to describe the parents' growth and link that to the offspring. Some candidates also gained marks for the idea of competition - but others missed out on marks because they did not mention 'competition' or didn't specify how the growth was affected. In (a)(ii), candidates gained marks for the idea of increased

40 nutrients. Some candidates wrote confused answers about nitrifying or denitrifying bacteria and some were unsure about what was being converted and what it was being converted into. A common mistake seen in several candidates was also to write about the idea of competition and that the bacteria were using up the nitrates. In (b)(i), most candidates used the term 'unwanted' to describe weeds. In (b)(ii), many candidates were able to score highly as they chose suitable examples of the resources the weeds would be competing for. In (b)(iii) most candidates were awarded the mark for suggesting using herbicide. Q7. (a) (i) The correct answer of B was seen on many scripts with A being the most common incorrect response. (ii) The correct answer of A was seen on many scripts with C being the most common incorrect response. (iii) The correct answer of C was seen on many scripts with A being the most common incorrect response. (b) (i) Zygote was the correct answer and was seen on many scripts. Common incorrect answers were embryo and fetus. There were also weak answers that simply described the process of fertilisation. (ii) Mitosis was the correct answer and was seen on many scripts. The term meiosis was the most common incorrect term seen. Candidates need to be careful when spelling biological terms as the examiners are not allowed to credit words spelt incorrectly, for example, meitosis. (iii) This question was surprisingly challenging for students. The correct answer required a tick in the box beside 'diploid with 46 chromosomes'. This was in evidence, but many candidates ticked this box and one other, or ticked a wrong box. This suggests that the terms haploid and diploid are not understood or that candidates cannot recall the number of chromosomes in a body cell. (c) Many candidates were aware that diffusion of nutrients from the mother's blood takes place at the placenta. Further credit was given for a valid description of how the structure of the placenta is adapted to its function. Credit was also given if the umbilical cord was mentioned. The question discriminated very well with the better answers giving excellent descriptions and the weaker answers expressing confusion, often making general references to human reproduction.

41 Q8. (a) required candidates to show the parents, gametes and possible offspring genotypes and phenotypes of a cross between parents with achondroplasia. Most were able to do this with some losing credit by failing to identify the phenotype of the offspring. Some seemed to think a sex linked allele was involved. In part (b) most could see that the probability of a second child being of average height is unaffected by the phenotype of the first child. Some candidates tried to express a probability as a ratio rather than a decimal or a fraction or percentage. In part (c) (i) the best candidates could explain a dominant allele as one that if present in the genotype is always expressed in the phenotype. Poorer responses used terms like stronger or more powerful and some candidates described a dominant allele as being more likely to be passed on. Part (c) (ii) candidates were asked to suggest why the number of people with achondroplasia is low, even though it is a dominant condition. We were expecting responses to refer to the allele having selective disadvantage and less achondroplasics reproducing leading to a low allele frequency. Q9. In (a), candidates were required to place stages of human reproduction in order and most responses were correct. Candidates then had to identify the differences between a diagram of a fetal heart and an adult heart in (b). Most were able to identify the gap between the atria and the joining of the aorta and pulmonary artery. In (c), most could identify the gender and give the correct number of chromosomes. Q10. This question provided a genetics question on flower colour in peas. In part (a) almost all could identify the dominant phenotype and most could explain how they knew. In (b) candidates had to suggest how Mendel could ensure that the purple F1 plants self-pollinated. The best responses suggested how he could isolate the plants and transfer pollen using a paintbrush. In (c) (i) candidates had to use a genetic diagram to show the offspring of selfing the F1 plants. Most could do this but some failed to gain full credit as they did not clearly show the gametes or the phenotypes of the offspring. In (i) most could calculate the ratio but only some could explain why the actual and observed ratio are different. In (d) candidates had to suggest how natural selection could affect the numbers of flowers since purple are more attractive to bees. Most candidates scored some marks with the best responses including the increased likelihood of purple pollen being carried and transferred to purple flowered plants. How this would lead to increased reproduction of purple flowered plants and how the purple allele would be

42 passed to future generations and how this would increase purple flowers and reduce white flowers. Q11. This question presented some novel information to candidates on ash borers. In (a) most were able to suggest that feeding on carbohydrates would give the maggots energy from respiration. Some were able to name active transport and describe how it enables absorption of ions against a concentration gradient. Most could also describe how magnesium ions are used for chlorophyll molecules required in photosynthesis. In part (b) candidates needed to explain how ash borers had evolved to look like wasps. Quite a number of candidates thought that the ash borer could mate with the wasp to acquire similar characteristics. The best answers described a mutation that caused the ash borer to inherit an allele that conferred a similarity to the wasp. This allele would mean a wasp like phenotype would be less likely to be attacked by predators. This advantage meant that these ash borers would be more likely to survive and mate. The allele for wasp features would then be passed on to their offspring. Over many generations the ash borer would evolve to look like a wasp. Q12. Part (a) of this question tested understanding of sex inheritance and was well answered by most students. A minority lost a mark for not stating the sex of the offspring and a very small number lost credit for using X and Y symbols rather that the ones given in the question. The remaining parts of this question were extremely well answered by the vast majority of students. Protein providing amino acids for growth was the most popular response in part (b)(i), most appreciated the role of the shell in protecting the developing embryo in (b)(ii), and a pleasing number knew a source and a function of vitamin A in (b)(iii). In part (c), most were able to gain full marks though there was occasionally evidence of confusion about the role of meiosis and mitosis. Q13. This question gave a diagram of a sperm cell and in (a) most students could give the number of chromosomes present in its nucleus. In (b) most could explain the importance of respiration in providing energy for the sperm to swim using its tail. In part (c) almost all could correctly calculate the number of sperm capable of swimming from the data provided. Part (d) described a fertility test that measures the oxygen use by respiring sperm. In (i) the best students realised that if the solution stayed purple no oxygen was

43 being used for respiration by the sperm so they must be dead or not moving. In (ii) the best answers explained that a break in the seal, a lack of temperature control or a small semen sample could make the results incorrect. Other students suggested that one sample may be atypical. Q14. This question was answered well by most students. Part (a) caused a few difficulties but most appreciated that being homozygous meant that there would be two of the same alleles present in the genotype. Choosing the correct genotypes in parts (a)(ii) and (b)(i) posed little difficulty and the correct answer of zero for the probability in part (b)(ii) was frequently seen. The correct answer of 22.8 million was often seen in (c)(i) but it was clear to examiners that many found this calculation a challenge. Common wrong answers were /315 = or 12/ = Again, markers were instructed to award one mark for an incorrect answer providing they could see the numbers 12 or 0.12 somewhere in the working. The final part of this question posed difficulty to many who made reference to the genotype of lactose intolerant people failing to appreciate that the question examined their understanding of how sample size impacts on the confidence that can be had with data. Q15. (a) The concept of a gene being a section of DNA that codes for a protein was known by the more able candidates. The idea that genes determine characteristics was also credited as an alternative to coding for a protein. Many answers simply discussed the fact that they are inherited or made loose references to chromosomes or nuclei. (b) The examiners were looking for answers that expressed the idea that superovulation would result in a greater quantity of eggs than normal. Many appreciated this and gained the mark. However, there were an abundance of answers that showed that the word 'super' was not understood and nor was the process of 'ovulation'. Poor answers simply reiterated information from the comprehension. (c) Most candidates recalled that the uterus is the place where embryos would implant in the surrogate mother, though a variety of other named female organs were named in the poorer answers. The non-technical term 'womb' was credited. (d) Most candidates were aware of the link between smoking and emphysema. Weaker answers showed no understanding of emphysema and tended to describe general aspects of human behaviour or make reference to AAT.

44 (e) The correct answer of 50% was seen in most scripts. (f) (i) There were some very good answers that were able to make a link between what might happen in the gut of a person which would not assist the clotting of blood. The passage stated that 'human proteins could be made in other mammals and extracted from their milk' so the examiners were looking for a comment that made it clear that the blood clotting factors (protein) would not be able to enter the bloodstream because they would be digested. Many candidates got close to being credited by making it clear that the blood clotting factors would not be able to get into the blood but then failed to say why. Many candidates simply repeated the wording of the question stating that blood clotting factors have to be extracted before being used, and many simply noted that blood clotting factors are needed to clot blood. (ii) Candidates described the role of cellulose as roughage to help peristalsis in the gut. This suggests that candidates should be encouraged to read questions carefully. The question required an appreciation that cellulose is made from glucose which is used in respiration and could help to increase cattle growth or milk and meat production. A surprising number of candidates seem to think that cellulose has a role in immunity. (g) Many candidates appreciated that producing transgenic hearts would increase availability for transplantation which would save lives, and also that the transgenic hearts are less likely to be rejected by the host. This question discriminated well with the better candidates making reference to at least three of these points and the weaker candidates only referring to one or none. Q16. This question presented a table of genotypes and phenotypes for wing length in Drosophila. Most were able to complete the table showing the genotype, description of genotype and phenotype. The most common omission was the description of ll as 'homozygous' rather than 'homozygous recessive'. In part (b) most students could calculate the expected number of Ll offspring from a Ll Ll cross. In (c) almost all could correctly draw a food chain to show how fruit flies feed on yeast growing on fruit. The few who did not gain full credit had the arrows facing the wrong way. In part (d) an investigation was described and students had to name the factors to control, most could do this. They were also able in (d)(ii) to suggest that the results of the investigation may be unreliable as the experiment was not repeated.

45 Q1. Q2.

46

47 Q3.

48 Q4.

49 Q5.

50 Q6.

51 Q7.

52 Q8.

53 Q9.

54 Q10.

55

56 Q11. Q12.

57 Q13.

58 Q14.

59 Q15.

60 Q16.

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