Topic 3/10 D [60 marks]

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1 Topic 3/10 D [60 marks] 1. The sequence of the first six amino acids of the normal β hemoglobin (Hb A) chain are listed. valine histidine leucine threonine proline glutamic acid Which sequence of amino acids could there be in the first six amino acids of the sickle-cell β hemoglobin (Hb S) chain? A. glutamic acid histidine leucine threonine proline valine. valine valine histidine leucine threonine proline C. glutamic acid histidine leucine threonine proline glutamic acid D. valine histidine leucine threonine proline valine D 2. What is the difference between the alleles of a gene? A. Their position on the chromosome. Their amino acid sequence C. Their pentose sugars D. Their base sequence D 3. Which is a characteristic of the haploid number of eukaryotic chromosomes? A. It doubles in mitosis.. It is fixed for each species. C. It is an even number for all species. D. It is positively correlated with an animal s mass. 4. What is characteristic of homologous chromosomes? A. They have an identical DNA sequence.. They are of the same length in karyograms. C. They form pairs in prokaryotes. D. They carry the same alleles.

2 5. What is a possible source of the chromosomes used for pre-natal karyotype diagnosis? A. The mother s lymphocytes. The mother s cheek cells C. The cells from chorionic villi D. The fetal hair root cells C 6. The micrographs show four different phases from meiosis II. What is the correct order? A C D C 7. What event occurs only in meiosis? A. Fusion of gametes to promote genetic variation. Random separation of chromatids C. Random separation of homologous chromosomes D. Replication of chromosomes C 8. What is the chromosome number in a human gamete with non-disjunction? A C. 24 D. 23

3 C 9. What proves that the inheritance of the condition shown in this pedigree chart is autosomal recessive and not autosomal dominant? A. There is no affected person in generation I.. oth males and females are affected. C. Two unaffected parents have a child that is affected. D. Not everybody in generation III is affected. C 10. In a human with type A blood, what determines the blood group? A. Sex chromosomes. One or two alleles C. Multiple alleles D. Codominant alleles 11. The feather colour of a certain breed of chicken is controlled by codominant alleles. A cross between a homozygous black-feathered chicken and a homozygous white-feathered chicken produces all speckled chickens. What phenotypic ratios would be expected from a cross between two speckled chickens? A. All speckled. 1 black feathers : 1 white feathers C. Speckled, black feathers and white feathers in equal numbers D. 1 black feathers : 2 speckled feathers : 1 white feathers D

4 How are enzymes used during gene transfer involving plasmids? 12. A 13. What was an aim of genetic modification of organisms? A. To provide stem cells from embryos for medical use. To make crop plants resistant to herbicides C. To provide sperm cells for in vitro fertilization (IVF) D. To produce genetically identical sheep Which statement about the polymerase chain reaction (PCR) is correct? 14. A. PCR allows DNA to be cloned in a test tube and millions of copies can be made in hours.. PCR allows the synthesis of RNA from DNA molecules. C. PCR is a natural process carried out by some viruses to amplify DNA molecules. D. PCR is a man-made technique used to identify the nucleotide sequence of DNA. A

5 Which gametes can result from the following crossover? 15. D 16. The genetic determination of dogs coats can be quite complex, with many different genes acting at the same time. The dominant allele E gives brown tones. The recessive allele e results in red tones. The colour intensity is due to another gene. The dominant allele gives a dark colour, whereas the recessive allele b results in a light colour. What would be the genotype of a light brown dog produced from a cross between a dark brown dog and a light red dog? A. EEbb. Eeb C. eeb D. Eebb

6 D 17. How many autosomes are there in a human sperm? A C. 23 D A test cross of linked genes was performed with fruit flies (Drosophila melanogaster). What is the most likely explanation for these results not fitting the expected ratio? A. Crossing-over. Non-disjunction C. Gene mutation D. Random variation A Why do humans inherit continuous variation with regard to height? 19. A. The trait for tallness is dominant.. The height phenotype is polygenic. C. This is a case of multiple alleles. D. Height in humans is polyclonal with multiple alleles. 20. What causes genetic variety in the formation of gametes during meiosis? A. Crossing over in prophase I and random orientation of homologous chromosomes in metaphase I. Crossing over in metaphase I and random orientation of homologous chromosomes in metaphase II C. Linkage of genes in prophase I and crossing over in metaphase I D. Linkage of genes in metaphase I and random orientation of homologous chromosomes in metaphase II

7 A Meiosis in humans produces cells that participate in fertilization. Outline the processes involved in meiosis. 21a. [5 marks] Remember, up to TWO quality of construction marks per essay. a. meiosis reduces a diploid cell into (four) haploid cell(s); b. (during prophase I) homologous chromosomes pair up/synapsis; c. chromatids (break and) recombine / crossing over d. (metaphase I) (homologous chromosomes) at the equator of the spindle / middle of cell; e. (anaphase I) (homologous) chromosomes separate and move to opposite poles; f. (telophase I) chromosomes reach poles and unwind WTTE; g. (prophase II) chromosomes (condense and) become visible, new spindles form; h. (metaphase II) chromosomes line up at the centre of the cells/equator; i. (anaphase II) sister chromatids separate; j. (telophase II) chromatids reach the poles and unwind; 21b. Following fertilization, cells in the developing embryo differentiate. Outline a technique for cloning using differentiated animal cells. [5 marks] Remember, up to TWO quality of construction marks per essay. a. differentiated/somatic/diploid cells taken from donor animal/sheep udder; b. (diploid) nucleus from donor cells removed; c. ova/eggs cells removed from (donor) animal/female sheep; d. (haploid) nucleus removed from eggs/ova; e. (diploid/donor s) nucleus is fused with/inserted into egg/ovum (to form zygote); f. embryo (from cell with donor nucleus and egg from surrogate) implanted in uterus of surrogate mother; g. normal pregnancy and birth is completed; h. offspring is a genetic copy/clone of the donor mother/diploid nucleus WTTE; State the name of the process used to produce the pattern of bands seen in the image. 22a. gel electrophoresis/dna profiling 22b. Determine, with a reason, which male is the father of the child. male 1 because all child s bands / alleles match either mother or male 1 / (approximately) half of bands match male 1 [1] Do not accept reference to genes.

8 23a. (i) State the technique used to collect cells for pre-natal testing. [3 marks] (ii) State the method used to arrange the chromosomes in a karyotype. (iii) State at what stage in the cell cycle the cells would be when this photograph was taken. (i) amniocentesis/sampling amniotic liquid/fluid (via needle)/chorionic villus sampling (ii) chromosomes are grouped by pairs according to size and structure/band pattern/location of centromeres (iii) metaphase/late prophase of mitosis 23b. Albinism is inherited as a recessive trait; the alleles of the gene involved are A and a. An individual with albinism produces little or no pigment in the eyes, skin and hair. In a family, one sister has albinism while the parents and other sister have normal pigmentation. [3 marks] (i) Determine, using a Punnett grid to show your reasoning, the possible genotypes of the sister with normal pigmentation. (ii) Deduce the probability that the next child of this couple will have albinism. (i) Punnett grid shows the gametes (A and a) on one axis and the gametes (A and a) on the other axis and genotypes (AA, Aa, Aa, and aa) of offspring; AA/homozygous dominant and Aa/heterozygous (show normal pigmentation); oth needed Do not award marks to any answer suggesting sex linkage. (ii) 1/4 /25 %/0.25 probability of albinism / 1 in 4 chance 24a. The correlation shown in the data above can be explained by natural selection. Outline how the process of natural selection can lead to evolution. [3 marks]

9 offspring compete/environment cannot support all offspring; (genetic) variation in the offspring; natural selection /survival of better adapted/fittest organisms; reproduction passes characteristics to other generations; allele frequencies change; malaria causes selection pressure (in Africa/worldwide); different hemoglobin/sickle-cell genotypes exist / normal hemoglobin and sicklecell alleles exist; natural selection/resistance to malaria of sickle-cell heterozygotes/allele; survivors pass on sickle-cell allele to offspring; ( do not accept sickle-cell anemia) frequency of sickle-cell allele highest in areas of high malaria incidence; 24b. Explain how a base substitution mutation, such as GAG to GTG, can lead to a disease like sickle-cell anemia. [2 marks] change in the codon (of the mrna); trna with a different anticodon attaches; (if codon changed) wrong/different amino acid is joined to peptide/glutamic acid replaced by valine; distorted hemoglobin molecule alters red blood cell shape/reduces ability to carry oxygen; 24c. Using a Punnett grid, determine the possible genotypes and phenotypes of a cross between a man and a woman who are both carriers of the sickle-cell allele. Use the symbol Hb S for the sickle-cell allele and Hb A for the normal allele. [2 marks] Phenotypes: (genotypes shown in a Punnett grid eg) (phenotypes) (Hb A Hb A) normal and (Hb A Hb S) normal carrier/intermediate/sickle-cell trait and (Hb S Hb S) sickle-cell anemia/diseased / (Hb A Hb A and Hb A Hb S) normal /symptomless and (Hb S Hb S) sickle-cell anemia/diseased; To award the mark all phenotypes must be mentioned.

10 Predict the genotypic and phenotypic ratios of the possible offspring of a male hemophiliac and a female carrier using suitable 25a. symbols for the alleles in a Punnett grid. [3 marks] Genotypic ratio: Phenotypic ratio: correctly constructed Punnett square with correct gamete genotypes; genotypic ratio: 1 XHX h : 1XhX h : 1 XHY : 1 XhY; (can be inferred from cells of Punnett square) phenotypic ratio: 1 female hemophiliac : 1 female carrier/non-hemophiliac : 1 male hemophiliac : 1 male normal/non-hemophiliac / 50 % hemophiliac : 50 % non-hemophiliac; Allow ECF. Award [2 max] if notation used does not indicate sex linkage, i.e. if cross is Hh hh. Hemophilia is a disorder where the ability to control blood clotting or coagulation is impaired. Describe the process of blood 25b. clotting. [2 marks] release of clotting factors from platelets/damaged cells; conversion of prothrombin to thrombin; thrombin catalyses the conversion of fibrinogen into fibrin; (insoluble) fibrin (net) captures blood cells; 26. Analyse this karyotype. [2 marks] Male has (one X and) one Y chromosome / X chromosome is bigger than Y chromosome; non-disjunction leads to three copies of chromosome 13/trisomy Explain the inheritance of colour blindness. [8 marks]

11 a. colour blindness caused by recessive allele / colour blindness is recessive; b. gene located on X chromosome/sex-linked; c. X b is allele for colour blindness and X is allele for normal colour vision/dominant allele; d. male has one X and one Y chromosome; e. male has only one copy of gene(s) located on X chromosome; f. X chromosome (in males) comes from female parent; g. any male receiving allele from mother will express the trait; h. XbY is genotype for colour blind male; i. many more males have colour blindness than females; j. female will express colour blindness only if is homozygous recessive/x b X b; k. heterozygous/x X b female is a carrier; l. colour blind female could be born to colour blind father and carrier mother; Marks may be earned for use of annotated diagram/punnett square to show points given above. Accept use of letters other than and b as long as capital letter is used for dominant and lower case letter for recessive alleles. For using other improper notation (not showing X or Y), award [0] for the first misuse and then apply ECF to additional notation as long as usage is consistent. (Plus up to [2] for quality) International accalaureate Organization 2018 International accalaureate - accalauréat International - achillerato Internacional Printed for Dubai American Academy