I. Very Short Answer Type Questions (1 Mark Each)
- Who coined the term 'gene' ?
W.Johannsen in 1910.
- What is the base of modern biotechnology ?
To understand the principles of inheritance of traits.
- Name the scientist who produced first hybrid between Dianthus barbetus and Dianthus caryophyllis in an interspecific cross.
Thomas Fairchild in 1717.
- Name the scientist who rediscovered Mendel's laws of heredity in 1900.
de Vries, Tschermak and Correns.
- Who coined the term 'Genetic' ?
Bateson in 1906.
- Who gave the concept of linkage ?
Bateson and Punnett in 1906.
- What is gene now-a-days ?
A gene is a stretch of DNA moleculle that codes for a specific protein through a messenger RNA molecule.
- Name the plant on which Mendel made his famous breeding experiments in 1956.
Garden pea or Pisum sativum.
- What does law of dominance explain ?
Alleles may be dominant or recessive and the dominant allele if present would determine the character, example: round shape of seed is dominant over wrinkled.
- Define incomplete dominance.
In incomplete dominance the genes of an allele morphic pair are not expressed as dominant and recessive but express themselves partially when present together in the hybrid and such genes are called intermediate genes.
- Who established relationship between chromosomes and Mendelian factors ?
Sutton and Boveri in 1902.
- Name the scientists who studied sex chromosomes in insects and Protenor.
McClung and Wilson et.al.
- Define allele.
Allele is defined "as different alternative forms of the same gene pair, each of which can affect the specific trait or character differently".
- Who coined the term 'allele' ?
- Define homozygous.
An individual having indentical genes for a trait is known as homozygous, example: AA, BB, TT or tt, cc, etc.
- What is heterozygous ?
An individual having dissimilar genes for a trait,example: Tt, Aa, Bb etc.
- What are multiple alleles ?
More than two allelic forms existing for certain genes at the same locus at a chromosome are called multiple alleles.
- Write the multiple allels for seed storage protein in wheat ?
|Glu - A1a
||HMW subunit 1
|Glu - A1b
||HMW subunit 2
|Glu - A1c
- Define linkage.
It is the tendency of genes to remain tied together during the process of inheritance.
- What is crossing over ?
It is the process that breaks the original linkage between the genes present in chromosomes.
- What is genetic recombination ?
The exchange of genetic material between homologus chromosomes.
- What are linkage groups ?
Many hereditary characters are associated in groups and these are called linkage groups.
- How many linkage groups are there in Drosophilia ?
There are 4 linkage groups in Drosophilia.
- Write the genetic distance for genetic mapping.
Centi Morgan (CM).
- What are two types of gene interactions ?
(i) Additive gene action
- What is gene interaction ?
Gene interaction is the phenomenon of gene action when two or more genes control phenotype and every gene has some effect which may be of different type.
- Define sex linked inheritance.
It is the inheritance of linked genes associated to sex chromosomes X and Y.
- Some traits are controlled by mitochondrial or chloroplast genes in a non Mendelian manner. What would you call this phenomenon ?
Extra nuclear or cytoplasmic inheritance.
- Define mutation.
Mutation is a hereditary change in the nucleotide sequence of DNA.
- What is a transposon ?
It is a DNA segment responsible for an assortment of genetic instability.
II. Short Answer Type Questions (2 Marks Each)
- Differentiate between complete dominance and incomplete dominance
Differentiate between incomplete dominance and Co-dominance :
|1. In incomplete dominance one of the
two allels shows the effect.
|1. In co-dominance both the alleles are
expressed equally in F1 individuals.
|2. Two allels of a pair interact and produce
an intermediate type.
|2. Both genes of an allelic pair contribute equally
to the phenotypic expression of the hybrid.
|3. Example : Flower colour in Mirabilis jalapa.
||3. Example : Roan in cattle.
- Write any two laws of inheritance as proposed by Mendel.
Mendel experimented on pea (Pisum sativum) and his results were published in paper entitled "Experiments on Plant Hybridization" in 1866.
Mendel's Laws of Inheritance :
(i) Law of dominance : It states that the alleles may be dominant or recessive. The dominant alleles express themselves to determine the trait, example: Tall is dominant over recessive in pea plants.
(ii) Law of segregation : The allels separate and segregate during gamete formation by meiosis cell division. Each gamete has only one of the two alleles present.
- How Mendel's law of segregation can be explained by the segregation of homologus chromosomes during meiosis ?
Chromosomes are called the vehicles of heredity. The contain genes or Mendelian factors on them. They transmit from one generation to the other during inheritance. Chromosomes duplicate during the interphase stage of cell cycle. Chromosomes separate during reduction or meiosis division. Chromosomes are found in pairs during meiosis. They become single during gamete formation.
- Define extranuclear inheritance. Enumerate the criteria shown by cytogenes.
Cytoplasmic inheritance is called extranuclear inheritance. It is the way of inheritance through the cytoplasmic genes and not by nuclear genes. Mitochondrial and chloroplast genes are also responsible for cytoplasmic inheritance.
(i) Lack of Mendelian segregation.
(ii) Persistence of traits over many generations.
(iii) Controlled by cytoplasmic genes, chloroplast or mitochondrial DNA.
(iv) Show maternal inheritance by way of egg cytoplasm.
(v) It is uniparental maternal inheritance.
Examples are shell coiling in snails (Limnea peregra), variegated leaves in 4 O'clock plant (Mirabilis jalapa ; its race albomaculata).
- Why are only some mutations lethal ?
Lethal mutations effect the survival of the organisms, example: albino seedlings of any plant are lethal because they do not have green pigment and so die due to lack of photosynthetic pigment. Haemophilia are lethal. Lethal mutations cause the death of the individuals. Lethal genes act in homozygous condition. In mice, there is a lethal gene which only act in homozygous condition. So homozygous mouse yellow dies but heterozygotes survive (Yy).
- If a gene had a mutation in the initiation codon, what will be its effect on its protein product ?
The initiation codon in prokaryotes is AUG. It codes for formylmet (formyl methionine) in prokaryotes. In eukaryotes AUG codes for methionine. Binding of charged formyl met tRNA to 30 S unit forms initiation complex. If there is mutation in the initiation codon it may result in deletion changing whole lots of condons. Such mutations are called Gabbrish mutations because they result in a sequence of codon that code for a polypeptide that make no sense. Protein synthesis would stop at non-sense codon and an incomplete protein will result.
- Explain DNA as the transforming principle.
DNA as the transforming principle : It was identified by Avery, Mac Leod and McCarty. They purified it from the debris of dead S-cells. Further they separated the various biomolecules found in the debris of the dead S-cells such as DNA, protein, sugar, lipids and RNA etc. They injected every component into live, non-visulant Type R cells to determine the transforming principle. DNA was the only material that produced type S cells when injected into the live R-cells. Thus Deoxyribonucleic acid was identified as the transforming principle.
- Difference between (a) Multiple alleles and (b) multiple genes.
||Three or more genes occupying a single locus
are called multiple alleles.
|Multiple genes are located on separate loci.
||They affect one character only.
||They affect one character but show polygenic
or cummulative effect.
||Example : wings in Drosophila show multiple allelism.
||Example : skin colour in human is shown by multiple genes.
III. Short Answer Type Questions (3 Marks Each)
- Differentiate between the mutagenic effect of alkylating agents, 5 bromouracil, intercalating agents and UV light.
Mutagenic effect of Alkylating Agents, 5 bromouracil, intercalating agents and UV light. Alkylating agent is a mutagen which adds alkyl groups example: methyl group (-CH3) and ethyl group to bases in DNA. EMS can alkylate T or G residues and cause them to mispair during replication of DNA causing transition (mutation type). The mutations may be reversed on induced by mutagens. If GT to AT transition mutation is caused by alkylating agents, it may be reversed by 5-bromouracil because it causes both types of transitions (AT to GC and GC to AT). Mutation caused by base analogue i.e., 5-bromo-uracil can be reversed by same mutagenic agent. Intercalating agents can slip into the sequence nitrogen bases and increase the distance between these bases. It can lead to deletion or addition in the DNA. Chemical mutagens are specific in mutation. uv- light causes base dimerization particularly photodimers (thymine-thymine dimers) 5-bromouracil is analogue of thymine base. It causes transition mutation by tantomeric shifts.
- Describe briefly two-ways in which a T-T dimers can be repaired by DNA repair mechanism.
Repair of T-T dimers by DNA repair mechanism : Enzyme system repairs damaged DNA (deoxyribonucleic acid). The enzyme removes damaged nucleotide.
(i) DNA Photoligase - Detoxication of superoxide radicals are produced during oxidative damage to DNA. By repair system mutations may be removed. Photodimer induced by uv-light can be reversed by DNA protolyase. It binds to photodimer and breaks up in light.
(ii) Nucleotide Excision Repair - Photodimers can be removed in dark by nucleotide excision repair eg., alkyl transferase enzyme removes alkyl groups (CH3 or C2H5 groups) added to nitrogen bases like Guanidine by alkylating mutagens.
Other repair mechanisms include post replication repair. Enzyme recognizes damage and makes single stranded nick at a few base pairs (bp) of either side of a damaged nucliotide. Then segment of DNA having the damaged nucleotide is removed by leaving a gap. The gap is then filled by DNA polymerase enzyme using template (remaining strand). The nicks are then sealed by DNA.