4.6 Inheritance, Variation Name: ________________________ and Evolution Higher Class: ________________________ Date: ________________________ Time: 405 minutes Marks: 402 marks Comments: Q1. Different antibiotics destroy bacteria in different ways. • Some antibiotics disrupt the bacterial cell membrane. • Some antibiotics disrupt the bacterial cell wall. (a) Antibiotics that disrupt the bacterial cell membrane often cause more side effects in humans compared with antibiotics that disrupt bacterial cell walls. Suggest why. ___________________________________________________________________ (1) (b) Some antibiotics prevent ribosomes functioning. Suggest how this damages the bacterium. ___________________________________________________________________ (1) (c) Drug manufacturers are spending less on research into new antibiotics. One reason why is because new antibiotics are rarely prescribed. Some people think that governments should pay drug manufacturers to develop new antibiotics. Suggest why. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ (3) (Total 5 marks) Q2. The figure below shows a carp. (a) A mutation causes a blue colour in some carp. What is a mutation? ___________________________________________________________________ ___________________________________________________________________ (1) (b) Suggest how a mutation could cause a different colour in carp. ___________________________________________________________________ ___________________________________________________________________ (1) (c) Two alleles control the body colour of carp: • brown (B) • blue (b). The brown allele is dominant to the blue allele. Two carp that are heterozygous for colour are crossed and produce 2.6 × 105 offspring. Approximately how many of the offspring are expected to be blue? Draw a genetic diagram to explain your answer. Give your answer in standard form. Number of offspring expected to be blue = ___________ (5) (d) A scientist wanted to find out whether a brown carp has the genotype BB or Bb. Describe what genetic cross a scientist could do to determine this. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ (2) (Total 9 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. ______________________________________________________________ (1) (ii) Give one reason in favour of embryo screening. ______________________________________________________________ (1) (Total 12 marks) Q4. A certain allele increases the chance of women developing one type of breast cancer. A woman has this allele. She wants to be sure that she will not have daughters who also have the allele. Doctors: • collect several eggs from her ovaries • fertilise the eggs with sperm, in dishes. (a) The doctors expect half the embryos produced to be female. Explain why. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ (2) (b) The embryos grow to around 100 cells. Doctors: • remove one cell from each embryo • check the cell for the allele. Complete the sentence. This process is known as embryo ______________________________ . (1) (c) One of the female embryos did not have the allele. This female embryo was implanted into the woman‟s uterus. Evaluate the advantages and disadvantages of the whole procedure. Use information from all parts of this question and your own knowledge. Remember to give a conclusion to your evaluation. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ (4) (Total 7 marks) Q5. The fruit fly, Drosophila, has either long wings or vestigial wings, as shown in the diagram. Long-winged fly Vestigial-winged fly The size of the wings is determined by a pair of alleles: A and a. Long-winged flies have one of two possible genotypes: AA or Aa. Vestigial-winged flies have only one genotype: aa. (a) (i) What is the genotype of a heterozygous fly? ______________________________________________________________ (1) (ii) Why can vestigial-winged flies only have the genotype aa? ______________________________________________________________ (1) (b) A male and a female long-winged fly were crossed. They produced 96 offspring. 72 of the offspring had long wings and 24 had vestigial wings. Use a genetic diagram to explain this. (4) (Total 6 marks) Q6. The black pigment in human skin and eyes is called melanin. Production of melanin is controlled by a single pair of genes. A person who is homozygous for a recessive allele of the gene has no melanin and is said to be albino. (a) A man is albino. His wife is heterozygous for the melanin-producing allele. (i) The fertilised egg cell produced by the couple divides to form two cells. Name the process of cell division involved. ______________________________________________________________ (1) (ii) How many albino genes would there be in each of these two cells? ______________________________________________________________ Explain you answer. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ (3) (b) (i) Albino people are more likely than people with melanin to suffer mutations that cause cancer in their skin. Suggest why albino people have an increased chance of mutation in their skin cells. ______________________________________________________________ ______________________________________________________________ (1) (ii) Sometimes, mutation in skin cells leads to cancers in other organs, such as the liver. Explain how. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ ______________________________________________________________