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Polydactyly is an inherited condition caused by a dominant allele. (a) The figure below shows the hand of a man with polydactyly. The man has an extra finger on each hand. The man’s mother also has polydactyly but his father does not. © Ifness/iStock (i) The man is heterozygous for polydactyly. Explain how the information given above shows that the man is heterozygous for polydactyly.
(3) (ii) The man marries a woman who does not have polydactyly. What is the probability that their first child will have polydactyly? (1)
(b) The man has red hair. His sister has brown hair. Both of their parents have brown hair. Brown hair is caused by the dominant allele, B. Red hair is caused by a recessive allele, b. Complete the genetic diagram below to show how the man’s parents were able to have some children with red hair and some with brown hair. Parental phenotypes Father Mother Parental Genotypes Gametes Offspring genotypes: Offspring phenotypes: (5) (Total 9 marks)
Read the information. Insects can be both useful and harmful to crop plants. Insects such as bees pollinate the flowers of some crop plants. Pollination is needed for successful sexual reproduction of crop plants. Some insects eat crops and other insects eat the insects that eat crops. Corn borers are insects that eat maize plants. A toxin produced by the bacterium Bacillus thuringiensis kills insects. Scientists grow Bacillus thuringiensis in large containers. The toxin is collected from the containers and is sprayed over maize crops to kill corn borers. A company has developed genetically modified (GM) maize plants. GM maize plants contain a gene from Bacillus thuringiensis. This gene changes the GM maize plants so that they produce the toxin.
(a) Describe how scientists can transfer the gene from Bacillus thuringiensis to maize plants. (3)
(b) Would you advise farmers to grow GM maize plants? Justify your answer by giving advantages and disadvantages of growing GM maize plants. Use the information from the box and your own knowledge to help you. (4) (Total 7 marks)
(b) Persons 7 and 8 are planning to have another baby. Use a genetic diagram to find the probability that the new baby will develop into a person with CADASIL. Use the following symbols to represent alleles. D = allele for CADASIL d = allele for not having CADASIL Probability = (4) (c) Scientists are trying to develop a treatment for CADASIL using stem cells. Specially treated stem cells would be injected into the damaged part of the brain. (i) Why do the scientists use stem cells? (2) (ii) Embryonic^ stem^ cells^ can^ be^ obtained^ by^ removing^ a^ few^ cells^ from^ a^ human^ embryo. In 2006 , scientists in Japan discovered how to change adult skin cells into stem cells. Suggest one advantage of using stem cells from adult skin cells. (1) (Total 10 marks)
Darwin suggested the theory of natural selection. (a) Explain how natural selection occurs. (3)
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. (1) (ii) Give one reason in favour of embryo screening. (1) (Total 12 marks)
(b) There are many different species of bird on the Earth today. Describe how these different species may have evolved from an ancestor such as Archaeopteryx. (4) (Total 8 marks)
Mark schemes
(a) (i) man has (inherited) polydactyly (PD) allele (from mother) 1 man has (inherited) other / normal / recessive allele from father 1 because father does not have PD allele or if father had it father would have had PD or father only has normal allele or father is homozygous recessive 1 allow gene for allele
(ii) 0.5 / ½ / 1 in 2 / 1:1 / 50% do not allow 1:2 or 50/ allow 50: 1 (b) parental phenotypes: both brown 1 parental genotypes: both Bb 1 gametes: B b and B b allow only on gametes answer line allow ecf from genotypes 1 offspring genotypes: BB (2)Bb bb allow ecf from gametes 1 offspring phenotypes correctly assigned to genotypes: BB & Bb = brown bb = red do not penalise confusion of ‘phenotypes’ &‘genotypes’ here 1 [9] (a) wing pattern similar to Amauris allow looks similar to Amauris 1
birds assume it will have an unpleasant taste 1 (b) mutation / variation produced wing pattern similar to Amauris do not accept breeds with Amauris do not accept idea of intentional adaptation 1 these butterflies not eaten (by birds) 1
(ii) 2 affected parents have unaffected child or 1 and 2 → 5 / 6 or if recessive all of 1 and 2 ’s children would have CADASIL 1 (iii) heterozygous^ –^ has unaffected children^ or^ because^ if^ homozygous all children would have CADASIL 1 (b) genetic diagram including: accept alternative symbols, if defined 1 correct gametes: D and d and d (and d ) ignore 7 / 8 or male / female 1 derivation of offspring genotypes: Dd Dd dd dd allow just Dd dd if ½-diagram allow ecf if correct for student’s gametes 1 identification of Dd as CADASIL or dd as unaffected allow ecf if correct for student’s gametes 1 correct probability: 0.5 / ½ / 1 in 2 / 50% / 1 : 1 1 (c) (i) stem cells can differentiate or are undifferentiated / unspecialised 1 can form blood vessel cells / brain cells or stem cells can divide 1
(ii) ethical argument^ -^ eg no risk of damage to embryo or adult can give consent for removal of cells or adult can re-grow skin more ethical qualified ignore religion unqualified or if from a relative then less chance of rejection or if from self then no chance of rejection or skin cells more accessible 1 [10] (a) variation (between organisms within species) allow described example allow mutation – but not if caused by change in conditions 1
those most suited / fittest survive 1 genes / alleles passed on (to offspring / next generation) allow mutation passed on 1 (b) (i) any two from: allow converse
- increase in latitude reduces number of (living) species ignore references to severity of conditions
- increase in latitude reduces time for evolution (of new species)
- the less the time to evolve the fewer the number of (living) species 2 (ii) any two from: do not accept intention or need to evolve
- (increase in latitude reduces number of (living) species because) less food / habitats / more competition at high latitude allow only extremophiles / well-adapted species can survive
- (increase in latitude reduces time for evolution (of new species) because) severe conditions act more quickly / to a greater extent on the weakest
- (the less the time to evolve the fewer the number of (living) species because) species that evolve slowly don’t survive 2 [7]
(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] (a) (i) any two from:
- (dead) animal buried in sediment allow imprint in mud hard parts / bones do not decay or soft parts dodecay allow (one of) the conditions for decay is missing − accept example, eg oxygen / water / correct temperature / bacteria mineralisation (of hard parts / bones) allow replacement by other materials 2
(ii) any two from:
- conditions not right for fossilisation ignore references to soft-bodied geological activity has destroyed fossils / has destroyed evidence allow a named / described example − eg vulcanism / earth movements / erosion fossils not yet found allow description of why not yet found 2
(b) any four from:
- separation / isolation (of different populations)
- different environmental conditions (between locations)
- mutation(s) occur or genetic variation (within each population)
- better adapted survive or natural selection occurs allow ‘survival of the fittest’ ignore animals adapt to their environment ignore reference to stronger survive favourable alleles passed on (in each population) allow genes for alleles eventually different populations unable to breed successfully with eachother allow unable to produce fertile offspring 4 [8]
