1. What is the full name of DNA?
Deoxyribonucleic acid
2. State the relationship between gene, DNA, protein and chromosome.
Gene is a segment of DNA which determines the body characteristics or traits.
DNA wraps around some proteins to form chromosome.
3. What type of substances does DNA belongs to?
Nucleic acid
4. How many types of nucleic acid are there? What are they?
Two types
They are:
(1) Deoxyribonucleic acid (DNA)
(2) ribonucleic acid (RNA)
5. What is the basic unit of DNA? What does this basic unit consist of (chemical composition/ structure)?
Basic unit: nucleotide
The chemical composition:
(1) phosphate group
(2) 5-carbon sugar
(3) nitrogenous base
6. How does a polynucleotide form?
The nucleotides are joined to one another between the sugar of one nucleotide and the phosphate group of the next.
The sugar and the phosphate group form a backbone. The nucleotides stick out of the sugar-phosphate backbone.
Note: Try draw out the structure of a polynucleotide.
7. What is the difference between the sugar of DNA and RNA?
DNA: deoxyribose
RNA: ribose
8. How many bases are there? What are the bases that DNA and RNA have?
There are a total of 5 types of bases.
Adenine(A), Thymine(T), Cytosine(C), Guanine(G), Uracil(U)
DNA has A, T, C and G.
RNA has A, U, C and G.
9. Which one, RNA or DNA is double stranded?
DNA
10. What are the features of DNA molecules?
(1) double stranded
(2) two polynucleotide strands run in opposite directions and twist around each other to form a double helix.
(3) The bases on one polynucleotide strand link up to the bases on another polynucleotide strand by hydrogen bonds.
(4) Base A pairs up with T, C pairs up with G. These rules are called complementary base pairing.
11. What is genetic code?
The base sequence of DNA which determines the amino acid sequence in a polypeptide.
12. State how gene determines the characteristics / traits of an organism.
The base sequence on the DNA strand of a gene determines the amino acid sequence in a polypeptide. The polypeptides will become proteins.
Therefore gene can control the cell to make which types of proteins.
The characteristics / traits of an organism are determined by a number of chemical reactions, and these chemical reactions need to be speed up by enzymes and all enzymes are proteins.
13. What is a gene locus?
The position of a gene on a chromosome.
14. State the relationship between gene, allele and homologous chromosome.
Every gene has two or more different forms, which occurs at the same position on a pair of homologous chromosomes, we called these different forms of the same gene alleles.
15. State the adaptive features of DNA which enable it to function as a genetic material.
(1) Consist of a large number of nucleotides, therefore can carry a large amount of genetic information.
(2) The DNA molecule is stable.
(3) The pairing of specific bases enables accurate replication of DNA.
16. State the process of DNA replication.
(1) The hydrogen bonds between the bases of two DNA strand break.
(2) Two DNA strands separates.
(3) The two separated DNA strands each acts as a template
(4) Free nucleotides complementary to the base on each template are added
one by one upon being catalyzed by the enzyme DNA polymerase.
(5) Lastly, two identical DNA molecules are formed.
17. After DNA replication, what is the difference between the new DNA molecule and the original DNA molecule?
The new DNA molecule consists of one strand belonging to the original DNA molecule and another newly synthesized strand.
18. What is monohybrid inheritance?
The type of inheritance which involves only one gene.
19. Differentiate between ‘characteristic’ and ‘contrasting characters’.
A ‘characteristic’ can have many ‘contrasting characters’
e.g. Height is a characteristic. Tall and short is contrasting characters.
20. What is the experiment that Mendel did regarding tall and short pea plants about?
1. Pure bred tall pea plants are cross pollinated with pure bred short pea plants.
2. All plants in the next generation (first filial generation) are tall.
3. F1 tall plants are self pollinated.
4. The second filial generation consists of tall and short plants in the ratio of 3:1.
21. How can self-pollination be prevented?
Remove the stamen before a flower matures.
22. What is the advantage of using pea plant?
(1) self-pollination can be carried out.
(2) can breed quickly
(3) clear contrasting characters.
23. What are the contents of Mendel’s hypothesis?
(1) A characteristic is controlled by a pair of allele.
(2) During gamete formation, alleles separate. Each gamete can only receive one allele.
(3) The pair of alleles of the first filial generation must come from the parent generation. One paternal and one maternal.
(4) Within the two alleles, the one that is ‘stronger’, which means the contrasting character it controls will be expressed in heterozygous condition, is called the ‘dominant allele’, the allele that is suppressed from expression (i.e. masked) is called the ‘recessive allele’.
24. What is homozygote? What is heterozygote?
Homozygote refers to an organism whose genotype of a particular characteristic(gene) contains two identical alleles.
Heterozygote refers to an organism whose genotype of a particular characteristic(gene) contains two different alleles.
Note: When we refer someone being a homozygote or a heterozygote, we
are referring to the person being a homozygote or a heterozygote of
ONE particular gene only.
25. What is the meaning of pure bred? What is the meaning of hybrid?
Pure-bred: Individuals developed from homozygotes.
Hybrid: Individuals developed from heterozygotes.
(note: Hybrid refers to an individual produced by crossing two individuals which are genetically different in one or more characteristics.
26. What is genotype? What is phenotype?
Genotype refers to the genetic make-up of an organism.
Phenotype refers to the appearance of a trait.
27. How can genotype be represented? (take the height of pea plant as an example)
(1) Pure-bred tall pea plant, pure-bred short pea plant, hybrid
(2) Use symbols to represent:
Let T represent the dominant allele for tall pea plant, and t represent the recessive for short pea plant.
TT, Tt, tt
28. What is dominant allele? What is recessive allele?
Dominant allele: The allele which can express itself in heterozygous condition.
Recessive allele: The allele which effect is masked in heterozygous
condition, i.e., it can only express itself in homozygous condition.
29. What is the Law of Segregation?
During gamete formation (i.e. meiotic cell division), alleles separate so that each gamete receives only one allele from each pair.
30. What is Mendel’s first law?
It is the Law of Segregation.
31. What is genetic diagram and punnett square?
Both of them are methods to represent results of genetic cross.
Genetic diagram makes use of lines to represent. Usually used in monohybrid inheritance;
Punnett square makes use of a table to represent. Usually used in dihybrid inheritance.
32. What should we pay attention to when drawing genetic diagrams?
1. The symbols must first be stated clearly! e.g.
T represents the allele that leads to tall plant (note: must say allele! Not gene)
T represents the allele that leads to short plant
2. Capital letter means dominant allele. Small letter means recessive allele
33. What is test cross?
Crossing an organism of unknown genotype with a homozygous recessive organism. From the phenotypic result, we can deduce the genotype of the organism of unknown genotype.
34. How can we use test cross to determine the genotype of an organism of unknown genotype?
If the contrasting characters are in the ratio of 1:1, that means the organism of unknown genotype is heterozygous.
If there is only one contrasting character, that means the organism of unknown genotype is homozygous.
35. What is dihybrid inheritance?
The genetic phenomenon when two genes are investigated at the same time.
36. What is Mendel’s second law?
During formation of gametes, the alleles of two different genes will assort independently. (i.e. the separation of alleles of one gene is independent of (will not be affected by) the separation of alleles of other genes.)
37. What is Law of Independent Assortment?
It is Mendel’s second law of inheritance.
38. How is blood type inherited in human?
The blood type of human belongs to the ABO system. There are three allele, which are
(1) A: Can produce antigen A
(2) B: Can produce antigen B
(3) O: Cannot produce any antigen
Possible genotypes of blood group A: AO, AA
Possible genotypes of blood gorup B: BO, BB
Possible genotype of blood group AB: AB
Possible genotype of blood group O: O
39. How is sex determined in humans?
By a pair of sex chromosome: X and Y
Male: XY
Female: XX
40. What is sex linkage?
Genes located on the sex chromosome (can be X and can be Y)
Therefore, the inheritance of sex-linked genes is related to sex, the ratio may be different for different sex.
41. How are genetic diagram drawn when sex-linkage is involved?
(1) must use XX and XY
(2) symbol of allele must be listed next to the relevant sex chromosome
(represented as a superscript or subscript)
42. What is pedigree?
A diagram showing the phenotype of parent generation and different filial generation.
43. How can we deduce whether an allele is dominant or recessive from a human pedigree?
(1) Find a pair of parents of which both of them have the same contrasting character (same phenotype).
(2) If the next generation shows a different contrasting character( different phenotype), then the contrasting character of the parent is dominant.
44. What are the types of variation?
(1) Continuous variation
(2) Discontinuous variation
45. What are the characteristics of continuous variation?
(1) normal distribution curve
(2) There is a continuous range of intermediate phenotypes between two
extreme characters.
(3) Usually determined by many genes.
(4) Some continuous variations are affected by environment.
46. What are the characteristics of discontinuous variation?
(1) There will only be a few distinct phenotype with NO intermediates.
(2) Usually determined by one gene / one pair of alleles.
47. What is the causes if variation?
1. Heredity
(1) Independent assortment of chromosomes at meiosis
(2) Crossing over at meiosis
(3) Random combination of gametes during fertilization
(4) MUTATION
2. Environment