1. TOPIC 4: GENETICS
TOPIC 4: GENETICS

2. 4.1: Chromosomes, genes, alleles and mutations

3. 4.1.1 Eukaryotic chromosome
STATE: Eukaryotic chromosomes are made of DNA and proteins

4. 4.1.2: Gene
Define gene: A heritable factor that controls a specific characteristic. It is a section of DNA that codes for making one or more polypeptides.

5. 4.1.2: Allele
Define allele: One specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the same gene.

6. 4.1.2: Genome
Define genome: The whole of the genetic information of an organism

7. 4.1.3: Gene Mutation
Define mutation: A change in the base sequence of a gene

8. 4.1.4:Sickle cell anaemia

9. CCU GUG GAG
amino proline VALINE glutamic acid
acids

11. 4.1.4:

12. 4.1.4

13. Explain the causes of sickle-cell anemia
Explain the causes of sickle-cell anemia. [8] M11/4/BIOLO/HP2/ENG/TZ2/XX
caused by gene mutation;
(sickle-cell anemia) due to a base substitution (mutation);
changes the code on the DNA;
which leads to a change in transcription / change in mRNA;
DNA changes from CTC to CAC/GAG to
GTG / mRNA changes from GAG to GUG;

(accept DNA changes from CTT to
CAT/GAA to GTA / mRNA changes
from GAA to GUA)
which (in turn) leads to a change in translation / change in polypeptide chain/
protein;
(the tRNA) adds the wrong amino acid to the polypeptide chain;
glutamic acid replaced by valine;
produces abnormal hemoglobin;
causing abnormal red blood cell/erythrocyte shape / sickle shape;
which lowers the ability to transport oxygen;
sickle-cell allele is codominant;
homozygote/HbS HbS have sickle cell anemia/is lethal / heterozygote/HbS HbA has
the sickle trait/is carrier (and is more resistant to malaria);

14. Explain the cause of sickle cell anemia and why it has been selected through natural selection. [8] M08/4/BIOLO/SP2/ENG/TZ1/XX+

15. Explain the effect of base substitution mutation in sickle cell anemia.
[3] N07/4/BIOLO/HP2/ENG/TZ0/XX+

17. One homologous pair of chromosomes in their non-duplicated form

18. Two homologous pairs of chromosomes
Two homologous pairs of chromosomes. Chromosomes are shown in their duplicated form.

19. DNA Replication

20. Define: Homologous chromosomes: matching pairs of chromosomes

21. 4.2: Meiosis
STATE: Meiosis is a reduction division of a diploid nucleus to form haploid nuclei
Diploid: # of chromosomes in a body (somatic) cell (2n)
Haploid: # of chromosomes in a sex cell (n)

22. Prophase I of Meiosis I
Homologous chromosomes pair up forming a synapsis and crossing over occurs
Nuclear membrane breaks down
Chromosomes condense and supercoil
Spindle microtubules develop from the centrioles.

23. Metaphase I of Meiosis I
Microtubules attach to chromosomes.
Homologous chromosomes are “pushed and pulled” by microtubles to the equator of the cell.

24. Anaphase I of Meiosis I
Homologous chromosomes separate and are pulled to opposite poles.
Chromosomes are still in their duplicated form.
Cytokinesis occurs

25. Telophase I of Meiosis I
Chromosomes arrive at the poles
Chromosomes number is reduced by half.
Chromosomes uncoil
New nuclear membrane reforms.
Microtubules break down

26. Prophase II of Meiosis II
Nuclear membrane breaks down
Chromosomes supercoil
Centrioles move to the poles and spindle microtubules develop

27. Metaphase II of Meiosis II
Spindle microtubules attach to chromosomes and move chromosomes to the equator of the cell

28. Anaphase II of Meiosis II
Sisiter chromatids separate (and are now are called chromosomes) are pulled towards opposite poles

29. Telophase II of Meiosis II
Chromosomes uncoil
Nuclear membrane reforms
Cytokinesis

30. Meiosis: Type of nuclear division in which one parent diploid
nucleus divides into four daughter haploid nuclei, each
genetically different to each other.

31. DNA replication in the S-phase of interphase

33. Homologous chromosomes separate in meiosis I

34. Sister chromatids separate in meiosis II

35. a A

36. A a A a

37. A a Aa AA A Aa aa a

38. 4.2.1: Meiosis

39. 4.2.2: Homologous Chromosomes

40. 4.2.3: Process of Meiosis

41. 4.2.3: Crossing over

42. 4.2.3: Stages of Meiosis

43. 4.2.4: Non-disjunction

44. Fertilization following Meiosis II error:
Trisomy 21: Down syndrome
What should happen

45. Non-disjunction

46. 4.2.5: Karyotyping
STATE: In karyotyping, chromosomes are arranged in pairs according to their size and structure

47. Normal Male

48. Normal Female

49. Chromosomes in their duplicate form

50. Gorilla Karyotype

51. Dog Karyotype

52. Sheep Karyotype

53. What is wrong here?

54. Down Syndrome

55. Describe the causes of Down syndrome. [5] M11/4/BIOLO/HP2/ENG/TZ2/XX
Down syndrome is caused by non-disjunction;
occurs during meiosis;
chromosome pairs fail to separate in meiosis I / chromatids in meiosis II /
anaphase II;
some gametes have an extra chromosome;
can lead to zygotes/individuals with an extra chromosome / individual has
47 chromosomes;
in Down syndrome this would be trisomy 21/extra chromosome 21;
increased probability with increased age of mother/ages of parents; [5 max]

56. The karyotype below shows the chromosomes from a person with Down syndrome. M11/4/BIOLO/SP2/ENG/TZ2/XX
State the evidence provided by the karyotype that shows this person has Down syndrome. [1]
Outline how Down syndrome occurs due to meiosis. [2]
(c) Determine, giving a reason, the sex of the person in the karyotype. [1]
(d) Explain briefly why males are more likely to inherit colour blindness than females. [2]

57. Explain how an error in meiosis can lead to Down syndrome
Explain how an error in meiosis can lead to Down syndrome. [8] M10/4/BIOLO/HP2/ENG/TZ2/XX+
non-disjunction;
chromosomes/chromatids do not separate / go to same pole;
non-separation of (homologous) chromosomes during anaphase I;
due to incorrect spindle attachment;
non-separation of chromatids during anaphase II;
due to centromeres not dividing;
occurs during gamete/sperm/egg formation;
less common in sperm than egg formation / function of parents' age;
Down syndrome due to extra chromosome 21;
sperm/egg/gamete receives two chromosomes of same type;
zygote/offspring with three chromosomes of same type / trisomy / total 47 chromosomes; [8 max]
Accept the above points in an appropriately annotated diagram.

58. What’s wrong?

60. What’s wrong here?

61. Klinefelter’s Syndrome

62. What’s wrong?

63. Patau’s Syndrome

64. Chronic Myelogenous Leukemia (CML)

65. Triploid Karyotype

66. What’s the problem?

67. What are the Symptoms of Edwards Syndrome?
About 25% of Edward's
syndrome victims die
before they are one month old,
10% live for one year.
Symptoms
*Growth deficiency
*Breathing difficulties
*Developmental delays

68. STATE: Karyotyping is performed using cells collected by chorionic villus sampling or amniocentesis, for pre natal diagnosis of chromosome abnormalities.
4.2.6:

70. 4.3: Theoretical Genetics

71. 4.3.1:Genotype / Phenotype
Genotype: The combination of alleles an individual has for a particular characteristic
Phenotype: The physical appearance of a feature

72. 4.3.1:Dominant / Recessive Alleles
Dominant allele: an allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state.
Recessive allele: an allele that only has an effect on the phenotype when present in the homozygous state.
brown eyes brown eyes blue eyes

73. 4.3.1: Co-dominant alleles
Codominant alleles: pairs of alleles that both affect the phenotype when present in a heterozygote.

75. 4.3.1: Locus
Locus: The particular position on homologous chromosomes of a gene.

76. 4.3.1:Homozygous / Heterozygous
Homozygous: Having two identical alleles of a gene.
Heterozygous: Having two different alleles of a gene.

77. 4.3.1:Carrier
Carrier: an individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele.

78. 4.3.1:Test Cross
Test cross: testing a suspected heterozygote by crossing it with a known homozygous recessive.

79. 4.3.2: Punnett Grid

80. 4.3.3 and 4.3.4: Multiple Alleles and Blood groups
STATE: Some genes have more than two alleles (multiple alleles)

81. 4.3.5: Sex chromosomes

82. 4.3.6: Sex linkage. Genes carried on the sex chromosomes
STATE: Some genes present on the X chromosome are absent from the shorter Y chromosome

83. 4.3.7: Sex linkage
STATE: A human female can be homozygous or heterozygous with respect to sex-linked genes.

84. 4.3.8: Sex linked diseases

85. Sex Linked disease

86. Explain, using an example, how females but not males can be carriers of some
recessive alleles. [4] M11/4/BIOLO/SP2/ENG/TZ1/XX

87. M10/4/BIOLO/HP2/ENG/TZ2/XX+
4. (a) Explain why carriers of sex-linked (X-linked) genes must be heterozygous.
[2]

88. (c) Describe the inheritance of colour blindness in humans.
M09/4/BIOLO/HP2/ENG/TZ2/XX

89. 4.3.12: Pedigree Chart

90. 4.4 Genetic Engineering and Other Aspects of Biotechnology

91. 4.4.1: PCR (polymerase chain reaction)

92. 4.4.2: Gel Electrophoresis
State: that, in gel electrophoresis, fragments of DNA move in an electric field and are separated according to their size.

93. Person A
Person B
DNA cut with restriction enzyme
3 fragments
2 fragments

97. 4.4.3 and 4.4.4: DNA Profiling
STATE: Gel electrophoresis of DNA is used in DNA profiling

98. Explain the methods and aims of DNA profiling
Explain the methods and aims of DNA profiling. [8] M10/4/BIOLO/HP2/ENG/TZ1/XX

99. 4.4.5: DNA profile

100. The diagram below represents the results of a paternity investigation
The diagram below represents the results of a paternity investigation. Track A is the
profile of the mother of a child, track B is the profile of the child and track C is the profile
of a man who might be the father. M11/4/BIOLO/SP2/ENG/TZ1/XX
Explain, using evidence from the diagram, whether this man is the father or not. [3]
M11/4/BIOLO/SP2/ENG/TZ1/XX

101. N07/4/BIOLO/SP2/ENG/TZ0/
The diagram below shows a DNA profiling of a family with five children. Segments of the
DNA inherited by some members of the family are shown as two dark bands in each column.
The DNA fragments are labelled A to F.
State two properties of the fragmented pieces of DNA which allow them to be separated in gel electrophoresis.
b. Determine which DNA fragment Son 2 inherited from his mother and which from
his father.
From his mother: From his father:
c. Identify the child that genetically most resembles one of the grandparents. [1]
d. Apart from determining family relationships, outline one other application for
DNA profiling.[1]

102. 4.4.6: Human Genome Project (HGP)

104. 4.4.6: Possible Advantages to the HGP (know three of these)
Improves our ability to conduct genetic screening for genetic disorders.
Improves our ability to develop new drugs for genetic diseases. (Molecular medicine).
Improves our ability to use DNA in the study of evolution and human dispersal out of Africa.
Match organ donors with recipients in transplant programs.
Elucidating the function of the large proportion of DNA we know little about.

105. 4.4.7: Gene Transfer

106. 4.4.7:
Transfer of Genetic Material
Across Species

108. (b) (i) Label the diagram below which shows a basic gene transfer. [2]
(ii) State two general types of enzymes used in gene transfer.[1]

109. (a) Gene transfer to bacteria often involves small circles of DNA into which genes can be
inserted. State the name of a small circle of DNA, used for DNA transfer, in bacteria.
(b) The diagram below shows a cut circle of DNA into which a gene is being inserted. Before
it can be transfered into a bacterium, the ring must be altered, using an enzyme.
M10/4/BIOLO/SP2/ENG/TZ1/XX
Outline what must be done next to complete the process of gene insertion into the
DNA circle, including the name of the enzyme that is used.
[2]
(c) Discuss the potential benefit and possible harm of one named example of gene transfer between species.

110. 4.4.7: Transfer of Genetic Material Across Species
State: That, when genes are transferred between species the amino acid sequence of polypeptides translated from them is unchanged- because the genetic code is universal.

111. 4.4.8: Gene Transfer

112. State: that, when genes are transferred between the amino acid sequence of polypeptides translated from them is unchanged- because the genetic code is universal.

113. The diagram below shows a cut circle of DNA into which a gene is being inserted. Before it can be transferred into a bacterium, the ring must be altered, using an enzyme. M10/4/BIOLO/SP2/ENG/TZ1/XX
Outline what must be done next to complete the process of gene insertion into the
DNA circle, including the name of the enzyme that is used. [2]
Discuss the potential benefit and possible harm of one named example of gene transfer
between species. [3]

114. Outline a basic technique for gene transfer involving plasmids
Outline a basic technique for gene transfer involving plasmids. [6] M08/4/BIOLO/HP2/ENG/TZ2/XX

115. 4.4.9: State two examples of Genetically Modified Crops or Animals
GOLDEN RICE
Golden rice is a variety of rice that has been genetically modified to produce beta-carotene (a precursor of vitamin A). Golden rice has the potential to prevent blindness or death in populations with vitamin A deficiency.
BT CORN
BT corn is a variety of corn that has been genetically modified to produce a bacterial toxin. The toxin is not harmful to people but it kills caterpillars. The advantage of BT corn is that it doesn't need to be sprayed with pesticides.

116. 4.4.10: Benefits/Harmful Effects of GMOs
Advantages of Genetically Modified corn are: 1) it increases profits for farmers by saving them the expense of spraying pesticides; 2) it keeps the price of corn lower for consumers; and 3) it saves the environment from toxic pesticides, which can pose heath risks to people and can kill non-target species that with important roles in the ecosystem.
Disadvantages are: 1) insect pests may develop resistance to the GM corn because continual exposure to the toxins will speed up the rate of natural selection; and 2) GM corn may produce toxic pollen, release it into the air, and harm beneficial species like the monarch butterfly(although recent studies do not support this claim).

117. Genetic modification involves the transfer of DNA from one species to another. Discuss
the potential benefits and possible harmful effects of one example of genetic modification in a named organism. [8] M07/4/BIOLO/SP2/ENG/TZ1/XX

118. Two examples of genetically modified crops or animals
1. Bt Maize
2. Golden rice
Describe the genetic modification to produce Bt Maize
Potential Benefits of Bt Maize
Possible harmful effects of Bt Maize

119. 4.4.11: Clone: Genetically identical organisms or a group of cells derived from a single parent cell.

120. 4.4.12: Outline a techniques for cloning using differentiated animal cells

121. 4.4.12: Cloning using Differentiated Cells

122. 4.4.13: Ethical Issues in Therapeutic Cloning in Humans

123. Therapeutic cloning is the creation of an embryo to supply embryonic stem cells for medical use.

124. 4.4.13: Discuss ethical issues of therapeutic cloning in humans
What is therapeutic cloning?
Arguments for therapeutic cloning
Arguments against therapeutic cloning