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Q1.
The diagram below shows the production of human sperm cells. (a) Name the organ where the processes shown in the diagram above take place.
(1) (b) (i) Not every cell in the diagram above contains the same amount of DNA. Cell A contains 6.6 picograms of DNA (1 picogram = 10-^12 grams). How much DNA is there in each of the following cells? Cell B _____________ picograms Cell C _____________ picograms Cell E _____________ picograms (2) (ii) How much DNA would there be in a fertilised egg cell? _____________________ picograms (1) (iii) A fertilised egg cell divides many times to form an embryo. Name this type of cell division.
(1) (c) After a baby is born, stem cells may be collected from the umbilical cord. These can be frozen and stored for possible use in the future. (i) What are stem cells?
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(2) (ii) Suggest why it is ethically more acceptable to take stem cells from an umbilical cord instead of using stem cells from a 4-day-old embryo produced by In Vitro Fertilisation (IVF).
(1) (iii) Stem cells taken from a child’s umbilical cord could be used to treat a condition later in that child’s life. Give one advantage of using the child’s own umbilical cord stem cells instead of using stem cells donated from another person.
(1) (iv) Why would it not be possible to treat a genetic disorder in a child using his own umbilical cord stem cells?
(1) (Total 10 marks)
Q2.
In 1866, Gregor Mendel published the results of his investigations into inheritance in garden pea plants. The diagram below shows the results Mendel obtained in one investigation with purple-flowered and white-flowered pea plants.
(2) (ii) Draw a genetic diagram to show how self-pollination of the F 1 purple-flowered plants produced mainly purple-flowered offspring in the F 2 generation together with some white-flowered offspring. Use the following symbols: N = allele for purple flower colour n = allele for white flower colour (3) (c) When Mendel published his work on genetics, other scientists at the time did not realise how important it was. Suggest two reasons why.
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(Total 10 marks)**
Q3.
Phenylketonuria (PKU) is an inherited condition. PKU makes people ill. (a) PKU is caused by a recessive allele. (i) What is an allele?
(1) (ii) What is meant by recessive?
(1) (b) The diagram below shows the inheritance of PKU in one family.
(i) Give one piece of evidence from the diagram that PKU is caused by a recessive allele.
(1) (ii) Persons 6 and 7 are planning to have another child. Use a genetic diagram to find the probability that the new child will have PKU. Use the following symbols in your answer: N = the dominant allele for not having PKU n = the recessive allele for PKU. Probability = _________________________ (4) (c) Persons 6 and 7 wish to avoid having another child with PKU. A genetic counsellor advises that they could produce several embryos by IVF treatment. (i) During IVF treatment, each fertilised egg cell forms an embryo by cell division. Name this type of cell division.
(1) (ii) An embryo screening technique could be used to find the genotype of each embryo. An unaffected embryo could then be placed in person 7 ’s uterus. The screening technique is carried out on a cell from an embryo after just three cell divisions of the fertilised egg. How many cells will there be in an embryo after the fertilised egg has divided three times? (1) (iii) During embryo screening, a technician tests the genetic material of the embryo to find out which alleles are present. The genetic material is made up of large molecules of a chemical substance. Name this chemical substance.
(1) (d) Some people have ethical objections to embryo screening. (i) Give one ethical objection to embryo screening.
Mark schemes
Q1.
(a) testis / testes allow testicle(s) 1 (b) (i) B = 13. C = 6. E = 3. all 3 correct = 2 marks 2 or 1 correct = 1 mark If no marks awarded allow ecf for C and E based on answer to B ie C = ½ B and E = ½ C for one mark 2 (ii) 6. allow twice answer for cell E in part bi 1 (iii) mitosis correct spelling only 1 (c) (i) any two from:
- cells that are able to divide
- undifferentiated cells / not specialised
- can become other types of cells / tissues or become specialised /differentiated allow pluripotent 2 (ii) 4 - day embryo is a (potential) human life or destroying/damaging (potential) human life allow cord would have been discarded anyway ignore reference to miscarriage allow cannot give consent 1 (iii) perfect tissue match or hard to find suitable donors allow same/matching antigens allow no danger of rejection allow no need to take immunosuppressant drugs (for life) ignore genetically identical or same DNA 1 (iv) stem cells have same faulty gene / allele / DNA / chromosomes allow genetically identical ignore cells have the same genetic disorder 1 [10]
Q2.
(a) (i) 3.15 : 1 accept 3.147:1 or 3.1 : 1 or 3 : 1 do not accept 3.14 : 1 Ignore 705: 1 (ii) any two from:
- fertilisation is random or ref. to chance combinations (of alleles / genes / chromosomes)
- more likely to get theoretical ratios or see (correct) pattern or get valid results if large number allow ref. to more representative / reliable do not allow more accurate or precise ignore fair / repeatable
- anomalies have limited effect / anomalies can be identified accept example of an anomaly 2 (b) (i) in sequence: Homozygous Homozygous Heterozygous All 3 correct = 2 marks 2 correct = 1 mark 1 or 0 correct = 0 marks 2 (ii) genetic diagram including: Parental genotypes: Nn and Nn allow other characters / symbols only if clearly defined 1 or Gametes: N and n + N and n derivation of offspring genotypes: NN Nn Nn nn allow genotypes correctly derived from candidate’s P gametes 1 identification: NN and Nn as purple and nn as white allow correct identification of candidate’s offspring genotypes but only if some F 2 are purple and some are white 1 (c) any two from:
- did not know about chromosomes / genes / DNA or did not know chromosomes occurred in pairs ignore genetics
- had pre-conceived theories eg blending of inherited characters ignore religious ideas unless qualified
1 (c) (i) mitosis correct spelling only 1 (ii) 8 1 (iii) DNA allow deoxyribonucleic acid do not allow RNA / ribonucleic acid 1 (d) (i) may lead to damage to embryo / may destroy embryos / embryo cannot give consent allow avoid abortion allow emotive terms – eg murder religious argument must be qualified allow ref to miscarriage allow idea of avoiding prejudice against disabled people allow idea of not producing designer babies 1 (ii) any one from:
- prevent having child with the disorder / prevent future suffering / reduce incidence of the disease ignore ref to having a healthy child ignore ref to selection of gender
- embryo cells could be used in stem cell treatment allow ref to long term cost of treating a child (with a disorder) allow ref to time for parents to become prepared 1 [12]
